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renovations 2017-10-10T17:28:45+00:00

Restauri scientifico conservativi

di palazzi posti sotto il vincolo

della Soprintendenza per i Beni Architettonici e Culturali

ZEB

mette a tua disposizione

tutta la sua cultura edile
su materiali e metodi antichi di lavorazione

La nostra esperienza

garantisce un risultato

di piena soddisfazione

I materiali utilizzati

per i restauri di edifici storici

sono spesso gli stessi utilizzati fin dall'epoca di dell'antica Roma

L'attenzione al dettaglio

è per noi fondamentale

facciamo restauri in tutti gli stili

e

risalenti

a tutte le epoche

Facciamo sempre

una minuziosa ricerca

dei materiali originari
dell'edificio oggetto di restauro

Scientific Conservative Renovations of architectural heritage under constraints

In conservative scientific restorations, each work is analyzed in its uniqueness by first evaluating the state of conservation, we try to understand its evolutionary history over the years, its transformative processes through a direct path (reading-stratigraphic analysis) and an indirect one (analysis of historical-archival sources), an assessment of damages and their causes, and then switch to an analysis of construction materials and constructive techniques.
For architectural recovery, we always try to intervene with original antique materials (old plates, bricks, beams, etc …) and where it is not possible to provide them with faithful reproductions, using however the raw material of the time manufactured following the same processing phases .
Our extensive knowledge of restorations, of traditional materials and techniques together with innovative technologies enables us to give our customers an outstanding result.
Definition
Structure
Plants
Floors
Finishes
Cocciopesto
Terrazzo flooring
Pozzolana

Definition

For “scientific restoration”, according to current legislation, is meant “interventions on buildings that have been of great importance in the urban context for specific qualities or architectural or artistic characters. Scientific restoration activities consist in a systematic set of works that, in the full respect of the typological, formal and structural elements of the building, allow its preservation, enhancing its character and making it possible to use it appropriately according to its intrinsic characteristics”.

The types of intervention includes:

1.Restoration of architectural aspects or restoration of altered parts, ie renovation or restoration of external and internal facades, renovation or restoration of internal environments, philological reconstruction of parts of the building eventually collapsed or demolished, preservation or restoration of the original organizational-distribution system, the preservation or restoration of free spaces, such as courts, wards, squares, places, gardens orchards and cloisters;

2.consolidation, with the replacement of non-recoverable parts without altering the position or the proportion of the following structural elements: – internal and external supporting walls; – floors and vaults; – stairs; – roof, with restoration of the original cover; the elimination of accretions as inconsistent parts of the original plant and its organic expansions;

3.the incorporation of essential technological and hygienic facilities.

For “restoration and restorative conservation” are meant “building interventions aimed at preserving the building organism and ensuring its functionality through a systematic set of works that, in keeping with the typological, formal and structural elements of the organism itself, allow uses compatible with them.
These interventions include the consolidation, restoration and renewal of building elements, the insertion of accessories and facilities required by the requirements of use, the elimination of elements outside the original building organization.

Even with regard to abusive interventions of scientific restoration or restorative conservation, , amnesty is only allowed for works complying with planning legislation.
In case they are also in accordance with the plan requirements, the works can be remitted without limitation. If they are compliant with planning laws, but contrary to the plan requirements, they can be remitted if the following limits and conditions are met.

First of all, it should be remembered that, as with all the abusive works carried out on buildings under constraints, even for these interventions the amnesty order requires the prior opinion of:
a) the law enforcement authority, in the case of constraints deriving from state or regional law (in this case the opinion is binding);
b) the Commission for architectural quality and landscape, in the case of buildings of historic-architectural value, bound by the municipal urban planning provisions (in this case the opinion is mandatory but not binding).

For the rest, the Regional Law subordinates the amnesty for abusive interventions for scientific restoration and conservative renovation to the respect of the same conditions as for interventions for building renovations:

– Prohibition of realization of new real estate units;
– respect of sanitary hygiene requirements;
– observance of the requisites for the recovery of living spaces of the attic;
– observance of the minimum number of pertinence parking spaces.

Structure

Our structural consolidation project involves the definition of the categories of works for the elimination of damages to the structure and the related causes. We therefore provide, where necessary, for structural consolidation that may concern arches, vaults, stone or brick walls, roofs, coverages, insoles, etc …

This activity also includes all the repair, reinforcement or replacement of individual structural elements (beams, architraves, insoles, pillars, wall panels) or parts of them which are not suitable for the structural function they must perform, provided that the intervention does not significantly change the overall behavior of the structure, especially for resistance to seismic actions, due to a not negligible variation in stiffness or weight.
Replacement of roofs and slabs may also be included in this category, provided that this does not result in a significant variation in stiffness in its plane, important for the redistribution of horizontal forces, or in an increase in static vertical loads.
Restoration or reinforcement of the connections between different structural elements (eg between walls, between walls and beams or insoles, including through the introduction of chains/tie-rods) fall into this category, as they still improve the overall behavior of the structure, especially with respect to seismic actions.
Interventions on structural elements, aimed at achieving local reinforcement and not just repair, will be aimed at eliminating the main structural shortage of the building, which cause the damages and the most commonly occurring collapse mechanisms due to earthquakes, thus achieving a higher level of building safety.
Therefore, for structural consolidation, are meant all those consolidations to restore the original static stability of the consolidated element.
Methods of intervention may vary according to the case, but here are the most common: consolidations by injecting binders, carbon fiber bandage consolidations, consolidations through tie-rods and chains, and finally consolidation by ‘cuci-scuci’ technique (unstitching/stitching).

Consolidations by Binder Injections
Old masonries, at times, have internal voids and discontinuities, shaped by disruptions or alteration phenomena of different nature. These cavities are interruptions in the matter of the wall structures and result in lesser resistance, especially if they are subject to increased loads, or to a different distribution or concentration of weights caused by disassociations or alterations of the ancient bearing sections (demolitions, openings, thinning, etc.).
The technique is to inject a binding blend at low pressure to strengthen the structure, incorporating the original mortar and helping to restore continuity to the system.
The injection consolidation technique usually takes place in the presence of a cracking state of stone, brick, or mixed masonry. It also applies to solving problems of adhesion loss and mutual collaboration between the construction parts (bricks, stones) resulting in a reduction in the mechanical strength of the assembly. Therefore, the application is suitable where an irregular and disjoint masonry is found, with widespread mortar degradation, which is dull, disintegrated or partially missing, with evident lesions in the structure.

Consolidations using carbon fiber bandage
The consolidation by carbon fiber bandage consists in attaching to the support, by means of adhesive resins, high-strength carbon-fiber bands.
The carbon fiber bandage can be used for the consolidation of stone or masonry vertical elements (columns, pillars, etc.).
Such intervention is particularly indicated in cases where it is necessary to restore the bearing of vertical elements of the structure mainly subject to compression, or if a prior consolidation is required (eg, for a change in use). Vertical elements compression overhangs are also used to improve static behavior in seismic events, as it does not result in increased weights and gives structures a remarkable adaptability.

Consolidations using tie-rods and chains
Tie-beams and chains, on the other hand, are constructive elements with a predominant linear development, traditionally employed in several types of construction with function of structural linking, containment, support, reinforcement and consolidation.
They generally counteract risks of shift, detachment, opening, collapse, and are therefore subjected to traction. The elements usually have prismatic, tubular or filamentary shape and length predominating with respect to the size of the cross-section, which can be circular, quadrangular or polygonal. Tie-beams and chains, moreover, often belong to more complex structures, for temporary or permanent consolidation, and can assume horizontal, vertical or inclined position according to the reasons for their work and the efforts they have to bear.
With regard to applications in the specific field of restoration, the technique involves installing such elements to contain abnormal thrusts, to counteract collapse, to reduce deformations or movements of structural elements, anchoring them to other parts of the artifacts, secure and stable, or to strengthen locally fragile structures that are unable to withstand the strains they are subjected to.

Consolidations using ‘cuci-scuci’ technique
Sometimes, masonry artifacts, affected by localized shortages or by larger portions where component parts are degraded, can be repaired by the so-called “cuci-scuci” technique (stitching/unstitching) which should actually be more properly named “scuci-cuci” (unstitching/stitching), because in them the destructive action precedes that constructive or integrative. The intervention is basically based on removing the damaged elements and then replacing them with other healthy elements, similar in shape, size, materials, and processing techniques, with respect to the removed ones.

In the case of unbound masonry, to consolidate and restore it, it is appropriate to re-aggregate all the components that make it, by making a grid of holes holes, using appropriate techniques, in which lime mortar is injected; verification of the results can be achieved by sonic tests before and after injections.
For some years now, conservative restoration is supported by the targeted use of composite materials such as carbon and various resins. In some specific situations we also propose the use of carbon fibers for structural reinforcement and the use of epoxy resins for the creation of doughs for prostheses for guarding wooden elements.

As far as the roofs go, we can find ceilings with suggestive ancient purlins, coffered ceilings, plankings, simple trusses king-post or not. The cover was generally hand-made tiles or clay tiles, wooden shingles, slabs of “piode” stone, slate, lead, etc.

Restoration, cleaning, consolidation, renovation or re-execution of lead or copper metal covers; ; traditional joining techniques are used, eg. the “triple bend, which best bear the considerable expansion to which the metal is subjected for thermal excursions; the traditional techniques are coupled with the use of durable materials, such as stainless steel, for crimping, thus combining traditional techniques with the best materials available at present.

Renovation from rising mists in masonry

In the masonry where water barrier systems have not been deployed, the phenomenon of the capillary rise is often evident. The building materials are porous, they absorb water that rises for capillarity and tries to evaporate from the masonry surfaces, depositing salts.

Raising moisture is a serious problem: not only involves aesthetic, structural and hygrothermal damage to the masonry, but it can also compromise the health in the living environments. It is known that moisture increases the vitality of germs and promotes migration of salts together with respiratory and rheumatic diseases. We have long been in implementing a mix of suitable solutions to permanently eliminate ascending moisture in the wall

Plants

Usually, in the buildings subject to conservative scientific restoration it is necessary to install or adapt the technological installations. (hydro-thermo-sanitary, electrical, lighting, elevators, fire-fighting, video surveillance, etc.). This is clearly a particularly tricky aspect of the work.
Our specialized staff arranges for the plant to be adapted to the rest of the building in a homogeneous way, for example lifting the floor to allow the plants to pass, then close it in the exact original position, or using materials that are well-masked with the rest of the context, or by making them under-trench, etc.

Floors

To restore, renovate or reproduce antique flooring, we have multiple accredited suppliers that can give us either retrieved material or faithfully reproduced material. Indispensable is the workmanship that needs to be qualified and experienced, which has always enabled us to respond perfectly in line with the aesthetic-architectural and functional needs of our customers.
The main types of floors are, depending on the place and the time, from terracotta floors, Venetian terraces, wooden, decorated clay, majolica, mosaics, cobblestones, stone, grits, etc …

We suggest taking a look at the images attached to help you get a clearer idea of all possible solutions.

Finishes

The finishes used in the historic buildings were infinite. There are many types and techniques of finishing both inside and outside, and various are the materials, ranging from stucco, pit lime, marble, mosaic, paintbrush …

We use all natural lime products.

Mortar bed:
Medium-sized granulometry, calibrated for brick and stone laying with traditional methods.

Stirring and grouting mortar:
Fine granulometry mortar, calibrated for grouting brick joints and stones, suitable for manual application and plastering machines.
Compared to the mortar bed, it is more fluidized and has longer grip times for greater workability.

The colors of the above mentioned mortars are obtained by mixing colored inerts and selected sands. They are not imitations, they are reproductions of historical originals.
The natural colors of mortars enhance the precious materials used in the construction of exposed masonry and are the natural complement to the historic masonry that is to be recovered.
The high purity of lime we use guarantees extremely low soluble salts content. Mortars do not release salt in the masonry: a feature that goes for an impeccable aesthetic result and a long duration of intervention.
Our mortars are porous and elastic. Just as the historical originals are able to adapt to the small settlements of the masonry without cracking and rapidly evaporate meteoric waters thus reducing the dangers of frost.

Thermo-insulating plaster with a crushed base (cocciopesto)
Natural lime mortar with excellent insulating properties, sound absorbing and good mechanical strength.
The widespread porosity of natural lime and milled cotto gives the product a high vapor permeability and a high degree of moisture control in the masonry.
Milled cotto was used in antiquity as well as for well-known pozzolanic features even for its thermal and hygrometer flywheel characteristics.
In the Roman hypocaust thermal baths, extensive use of “cocciopesto” plasterwork was performed in terms of both thermal storage and moisture absorption of hot fumes.
Our natural calcareous and natural perlite plaster preserves this concept, where the cocciopesto absorbs and expels excess moisture in the masonry as vapor; only a perfectly dry plaster can also guarantee the thermal conductivity values found in the laboratory.
Very often the walls have areas with higher thermal conductivity.
These areas known as thermal bridges can have a not negligible effect in determining thermal dispersions.
The external insulation made, allows to use the thermal accumulation of the wall to mitigate the transmission of daily temperature oscillations: the indoor environment will retain longer comfort conditions without additional energy inputs for overall heating or cooling through walls that can cause condensation, which lead to the rapid deterioration of the interior finishes with stains and molds.
The product applied as an external plaster eliminates thermal bridges, ensuring maximum homogeneity of thermal transmittance values, which results in energy savings and greater comfort in the home.
Insulating material of mineral origin (perlite) is embedded as a plaster inert: coat insulation is then made with materials of physical and mechanical behavior similar to that of masonry. This reduces the dangers of exfoliation and detachment of the various layers.

Thermo-insulating plaster with lime base
Natural lime mortar with excellent insulating properties, sound absorbing and good mechanical strength.
The widespread porosity of natural lime gives the product a high vapor permeability that prevents condensation phenomena.
Very often, the walls have areas with higher thermal conductivity, these zones known as thermal bridges can have a negligible effect in determining overall thermal dispersions through the walls and can cause condensation, which lead to the rapid deterioration of the interior finishes with presence of stains and molds. The product, applied as an external plaster, eliminates thermal bridges, ensuring maximum homogeneity of thermal transmittance values, which results in energy savings and greater comfort in the home.
The exterior insulation that is made allows to utilize the thermal storage capacity of the wall to mitigate the transmission of daily temperature oscillations: the indoor environment will retain longer comfort conditions without further energy input for heating or cooling.
Insulating material of mineral origin (perlite) is embedded as a plaster inert: coat insulation is then made with materials of physical and mechanical behavior similar to that of masonry. This reduces the dangers of exfoliation and detachment of the various layers.

Consolidating concrete
Breathable concrete with high adhesion and low elastic properties for the consolidation of decaying masonry.
Suitable for:
• plate structural reinforcement with net reinforcement.
• surface consolidation of masonry with bricks and broken stones.
Suitable for the consolidation of all masonry, brick, stone or mixed or unmanageable masonry, which require non-aggressive consolidation for their technical physical balance.
Only natural lime materials and natural reagents such as “pozzolana” are able to respect the binders and mortars that constitute the bedding of historic masonry.

Skimming plaster
The skimming plaster is a regularization lime based on common lime, natural hydraulic lime and inerts selected with low elastic modulus and excellent machinability.
It is mainly used to regularize both the disposal and the absorption of façades with different plaster or made in different times.
This mixture is indicated for leveling irregular bottoms, ensuring a secure grip on the hydraulic bases providing the best bonding bridge for subsequent natural lime finishes.

Marmorino
Marmorino is a smooth mortar for interior and exterior plaster, based on aged pit-lime mortar and powders and marble grits.
It has a stable and weather-resistant color as it is created with the exclusive use of natural earths and marble powders.
We have the ability to create it as a sample (as a copy of the original originals) or at the full discretion of the professional or of the customer in both in terms of colour or of granulometric curves.
The marmorino, made on the basis of the ancient Venetian original marble recipe can be iron polished to obtain surfaces of particular hardness and mechanical resistance, which are permeable to vapor but water-repellent.

Intonachino arenino
Colored, natural and breathable finishing plaster. It is a natural lime valuable finishing with a high degree of evaporation of masonry moisture.
It has a stable and weather-resistant color as it is made with the exclusive use of natural lherths and marble powders.
Because it is a natural lime mortar with a widespread porosity that allows an optimal exchange of steam between masonry and environment. It combines excellent mechanical resistance and maximum breathability.
Its coloration is lasting because the color is obtained by mixing colored inerts and natural coloring earths, materials that cannot be altered by weather and and UV. The aging process is identical to that of historic plaster: in time it acquires a softness of color and a coating that enhances its decorative features.
It can be applied and finished with many techniques from simple lamination to the lamination that makes it resemble natural stone, washing techniques, glazing…

Venetian Stucco or putty lime
Venetian stucco is a technique through which can be obtained a very particular finishing for the walls. With this technique several layers are applied through the aid of a spatula, so that the various layers give the impression of relief.
Venetian stucco can also be defined in other ways in relation to the composition of the products that are used to achieve this particular effect, ie smoothed lime, stucco lime, and lime “grassello”. These names derive from its composition: it is composed of lime, lime and water lime mixed with impalpable powder of marble.
At the end of the work you can get a glossy, smooth, opaque or relief effect.
It has to be said that the Venetian stucco name is probably due to the fact that although it is an ancient techniques (probably in Iran already existed since 5000 years ago), it arrived much later in our country, and the location where it was used for the first time is Venice, where, besides for ornamental reasons, the houses needed this finish to protect the walls from the humidity and the rise of the sea waters that touches the walls of the houses right from the foundations.

Cocciopesto

Pliny the Elder (I century BC) tells that Caio Proculeius, who enjoyed the trust of Caesar Augustus, died drinking a plaster solution because of a painful duodenal ulcer. The pharmacopoeia at the time taught much more remedies, however: the substance used in medicine was lime, not plaster. The mistake was fatal to the gentleman Proculeius, unless you think he wanted to do the foolish gesture deliberately. In the latter caseit is supposed that he too well knew, since then, the difference between an air and water binders.
Still from Plinio we learn that at that time the lime was widely used for the preparation of creams, cataplasmas and ointments. Lime, it is remembered, was used when it was still young and alive; it was used to burn, dissolve, extract and stop every beginning of serpiginous ulceration. Mixed with vinegar and rose oil, or applied with wax, even mixed with rose oil, it made every plague to heal.
It was also taught that it would cure all sorts of dislocation and swelling mixed with liquid resin, or with pig fat and honey. It is unbelievable how the same doughs were also suggested for the preparation of mortars to form the plasters intended for the protection of the walls of the buildings. The art of the plasterer, in fact, provided that the mastic should be prepared with fresh lime; it had to be extinguished in a pile of wine and, to soften it, pig fat and figs were added. Then it was, long and diligently, well beaten with “baculus” (particular sticks) and rammers. So prepared, it is said, mortar became the most tenacious thing ever to overcome any stone in hardness. The rule meant that the wall supports were wetted with oil, and then covered with such mastics.
These plasterings, which were prepared according to the strictest rules of the artisans of the time, were modified with small variants, which were distinctive of this or that stucco-craftsman.
In this regard, Pliny gives us a significant example: he tells that in Elide there was a temple dedicated to Minerva, where the brother of Fidia, Paneno, applied to the walls a plaster, that he had prepared, adding to the mastic milk and crocus powder. It is said that the unbelievers, even after a long time of application, were invited to moisten their thumb and touch the Opus Albarium to taste the delicacy of the flavor and the scent of saffron.
Regardless of the local variations and the artistic variations of the individual, the mastics prepared with the intent of making them endure the vantage of time, and, above all, the torment of water, all derive from
the ancient use of the plasters invented for coating the internal surfaces of water supply tanks. Their function and the knowledge of their preparation probably dates back to the periods when the first water deposits were built; the perfection of this practice has given for centuries a uniformity to the whole culture of the building of all civilized peoples, with ways, gestures and knowledge that have always been passed down and repeated. The thick layers of Opus Signinum, covering the interior of the tanks of the Solomon period in Israel, and the heavy plastering of cocciopesto, of the Abbot Mattia, appear to be composed and applied in the same manner.

Abbot Carlo Mattia, contemporary of the Scamozzi, belonging to the third order of Saint Francis, in the second decade of the sixteenth century, in his “Treaty of Architecture”, widely talks about “enamels over both covered and uncovered terraces”.
The experience of Abbot Mattia, on the other hand, resembles very much the requirements of the architect Francesco di Giorgio Martini, which foresees that the plaster of the terraces was “well-mixed with lard and oil needed as requested”, with the specific purpose of waterproofing them.
Our ancient predecessors seem to have a clear idea of the concept of “affinity” between matter. This concept, largely discussed in the nineteenth-century manuals, was derived from the awareness of the beneficial interaction and the positive influence between similar or miscible substances.
“Lime becomes increasingly better and more perfect along time, but mixed with friendly materials such as crushed bricks or crushed cobblestones or similar, than it makes a very big grip in the walls and particularly on plasters.” This way Scamozzi defines the two substances, lime and cocciopesto: “friendly matter”. To put together lime and cocciopesto means to give mortars, made up of these two materials, a hydraulic character that otherwise would not be, using common sands instead of cocciopesto. Between the two substances there is in fact a chemical affinity rather than a mechanical one, and it is, however, the same affinity as the fictile material, which forms the masonry, has with lime mortars. “Affinity with mortars” is the important requirement for which stones and sands adhere to cement binders.
Two causes affect this property: affinity can only be “mechanical” or even “chemical”. The affinity with the mortars in part is due to the fact that these, by their pasty nature, occupy in a masonry, all the interstices and roughness of the stones against which the mortar is compressed

The set of all these small engagements constitutes the “mechanical affinity”, which in general is not strong.
Some mortars, especially those made of high quality lime and fine sand, which are in contact with the stones, adhere not only mechanically but also chemically, combining with some elements of the stones (silica, alumina, iron oxides, etc.) so that when it is hardened it can be said that mortar forms a single and continuous body with stones. This adhesion constitutes the chemical affinity, which may also be greater than the cohesion of the mortar itself. The detachment of two cemented stones, in fact, in not always a neat cut: disjointed stones always carry the impression of mortars with them. Consequently, in the mechanical affinity takes action the structure of the stones and the degree of machining of their faces. The rough and cavernous stones are, the best adhere to the mortar. On the chemical affinity, it affects the composition of the rocks. Ordinarily, silica rocks and silicates react with mortar lime more than carbonates and sulphates.
These notions were exploited by past artisans especially in the preparation of cocciopesto mortars. There is no doubt that the use of Signina mortars was not just a surrogate of the Pozzolanic mortars, where the latter was lacking. The Romans often used together in their dense wall structures, lime and pozzolana mortars with lime and
cocciopesto plaster.

In many cases, the false conviction that cocciopesto plaster is impermeable is true: in fact, it is more permeable to water than the brick coatings on which they are laid. Lime and cocciopesto plasterwork needed (and currently need) to homogenize the surface of the underlying media, ie they should act as extension of the masonry itself with a seamless monolithic layer.
On this thick crust, the layer of mortar was made impermeable by virtue of the presence of oils, or similar substances, mixed therewith. It is true, however, that the signina mortar (reddish mortar with the addition of small fragments of ceramic), when dried, becomes solid with the masonry by chemical affinity. The calcium hydroxide that forms the binder [Ca (OH) 2], or air lime, reacts with the silica-aluminates (SiO2 + A12O3) contained in the mixture consisting of sand-blasted bricks, triggering a hydraulic setting pozzolanic process. The more porous the bricks will be, the higher the exchange surface of that reaction. It is therefore concluded that the most reactive cocciopesto is obtained from cooked bricks, at a relatively low temperature since more porous.
Likewise, for the same reason, the lime that constitutes mortar reacts with the hydraulically active components of the clay material on the substrate by bonding with it for chemical affinity. The hydraulic bond with the support will be the more rooted, the more profoundly the lime can be penetrated into the porous bricks in contact with the mortar.

The ancient rule taught to penetrate the lime in the deepest meanders and the porosity of the bricks, consisted of soaking the wall up to saturation, so that the lime overlaid it to the widest possible extent inside the cotto to hydraulically react with the most intimate layers of matter. Hence the reason for the repeated beating of fresh malt. Beating the mortar also meant to push the lime granules inside the porosity, draining them from the contained water. On this practice, the designers of all times express and make reference to them in their capitulations. Juvara, for example, with exasperated obstinacy, demands that his masters bounce the bricks in a water tank before using them.
The meticulous Viola Zanini recommends:
“They also have the walls to be so wet that by throwing further water, it will slide down without stopping over the wall, letting the wall getting wet through, so that if you get close to the wall with your ear, you cannot hear any more the noise of frying; this will give a sign of being wet enough. ”

In the past, tradition has always taught that refraining from soaking the wall and saving on the water could cause damage to the lime, as well as it would have been damaged if, in mixing the mortar, this had been too much, because using too much water in mixtures would keep away the lime particles that, in the end, would be badly tied in a too weak grip.
To be sure that the water in the mortar was not too much or too little, the rule required that the masonry be well wet and that the mortars should be kneaded with all the water it needed to make it pasty and workable. When the plaster had been well laid in thin strips, it was wanted that this was well-beaten with aq plastering trowel, so that the sands and the cocciopesto were well constipated in the vacuities created by the possible excess of water. In doing this, it would appear on the surface the undesired excess of water that had to be removed, smoothing the surface with the trowel, and then leaving the mortar well dry in the air.
It has often been argued that the beaten plaster is the most resistant because well-pressed calcine makes a good grip by wrapping sand and grain granules in cement.
In the case of the cocciopesto, however, it is improper to say that the lime wraps the crushed brick grains; It should be more accurately referred to the lime interpenetration in the sands of cocciopesto through their many porosity.
From comparative analysis using SEM (Electron Scanning Microscope), among several samples of lime and cocciopesto conglomerates, it can be seen that the oldest artifacts, which are more compact and constipated, thanks to a more accurate beating work, have a deeper rooting of lime inside roasted clay clusters, resulting in higher presence of hydraulic elements. In some cases the finest clasts seem to be completely dissolved in the lime, and the artifact looks like it is “all solid.” The reason why some lime and cocciopesto artifacts nowadays do not yield the same results of the more ancient ones, lies in neglecting some of the indispensable rules: in the past the raw material was surely obtained from the grinding of old tiles and bricks cooked in a traditional way, with ow temperature, while mortars, prepared with good lime, as we already said, were well pressed during their application.

Today, apart the forgotten practice of wetting the walls and beating fresh plaster, it is not always possible to have waste of original bricks, and if you want to prepare signina mortar mixture, sometimes you have to resort to use of modern bricks blocks, not very porous, or bricks made from clay cooked at relatively high temperatures.
The disappointment that some operators encounter, and which sometimes leads to unusual contributions of cement binder, derives precisely from this: clay materials cooked at high temperature, unfortunately are of no use to cause pozzolanic effects in mortars. It is well known that only bricks cooked at temperatures around 900 ° C can have a good pozzolanic activity, which, as said, stands in fixing calcium hydrate, present in fat slaked lime, giving rise to a hardening phenomenon with peculiarly hydraulic characteristics and not properly air ones. This is due essentially to the presence of soluble and aluminised silicates that are the material of any clay that has been calcined at the above temperature. It is then recognized, as is the case of pozzolanic mortars, that the process of grafting mortar, known as “hardening”, takes place in long, indeed very long times.
In this regard, consider that, in the nucleus of some Roman Opus Caementitium, two thousand years old, mortars are still reacting with the pozzolane and the cocciopesto cemented in them; and the extraordinary binding time, which does not give a sign of wanting to end, allows for large plastic deformations for the benefit of the stability of the artifacts, and on the other hand it allows the continuous transformation of hydraulically active substances, which continue to strengthen and strengthen the artifacts along the centuries. From this we can conclude that mortars made of lime and cocciopesto, or any other matter with pozzolanic virtues, can improve over time.

On the thick layers of cocciopesto mortar, which covered the interior of the tanks, the Romans applied a tempered Opus Marmoratum with oils and other organic matter, laid out in several layers and polished to perfection. When the plaster had dried well, other oil and animal fat were rubbed. Even in the setting of surface layers, alike during the application of the underlying mortar, the material was violently and repeatedly beaten in order to penetrate the lime of the marble work in the porosity of plaster; and the prolonged smoothing of the plaster made using tools with metal blades, up to giving the appearance and texture of a stone, made that the scaly sands on the surface, were all flat, next to each other, such as scales of a fish, making the finished work extraordinarily resistant to contact.
Whoever wants to fully realize what I’m saying, touch the plasterwork of the Baths of Scolastica in ancient Ephesus in Anatolia; the Opus Signinum of these plaster is a palm thick (7.5 cm) and is finished with a thick marble crust (1.8 cm); in that place you can easily notice that the enviable plasters are still tensely tangled to the bessales ( particular roman bricks) of the underlying Opus Mixtum, and still stand superbly at the ruin and abandonment of the centuries.

Another beautiful and peculiar example of waterproof plaster, can be admired at the Rocca dei Guidi di Modigliana (915-1376), near Forlì. Archaeological excavations have brought to light a striking rainfall, filtering and containment system for rainwater. The inner surface of the three superimposed domes and the cylinder that contains them, which serves as a filter, are plastered with a thick layer of cocciopesto mortar and finished with an oily putty even of cocciopesto. This technique, that recalls the fascinating shaped finishing with bricks, typical of that area, does not make use of the superficial Opus Marmoratum. This does not mean that the artifact was not, at the time, properly treated to get impenetrable to water. In fact, a cocciopesto plaster, although well-beaten and assorted, has a porosity superior to any other marbled crust. Therefore, these artifacts are much more oil greedy than the common lime and sand plasters; indeed, these substances never seem to be satiated and absorb the oil until it penetrates into their deepest and intimate emptiness, giving the entire layer of plaster, when dried, an extraordinary fluid containment power.

In the nineteenth century, an era of utmost curiosity, many researchers and industrialists worked with great zeal to re-propose, in a modern way, pastes and oily enamels used in the past. In fact, these modern oily mastics, which voluptuously acquired the name of the new industrialist who produced them, were nothing but the same Vitruvian dough added with substances that made them more workable and quick to dry. The most common, perhaps, already proposed at the end of the eighteenth century, was a mixture of lime, brick powder, silica sand, litharge (PbO) and linseed oil; all matters discussed so far, except litharge.
Litharge, used in the past for the preparation of oily stuccoes for patchworks, is nothing more than lead oxide, that is a crystalline powder, yellowish, heavy, and insoluble in common solvents.
Francesco Martini, for example, with the intent of sealing cracks and clefts in the already-formed plaster, inside the tanks, prescribes that ” use every day a trowel coating mixed olive oil or lard repeatedly until you will see water resist. If no plaster is suitable to tighten any slit or crack which in springs, tanks or other basin, put liquid paint, lime mortar, litharge, sulphur powder and mastics. ”
Litharge, nitric acid-soluble, such as the minio and the white lead powder, was added to the dough with the aim of thickening and rendering the oils dry. More simple and innocuous than common antique mastics.
Yemen’s Qadad has always consisted of white lime, lava and basalt broken granules, vegetable fats and oils (whose source was always kept secret), egg whites and, someone claims, even bovines brain.

Numidia’s Tabbì, for its ancient tradition, is obtained from the mixture of fat lime, silica sand, wood ash and oil extracted from a typical local berry named Argan. These doughs are still being mixed today by beating them with long sticks for days without intermission; when the material is pasty and compact, it is laid on the brick walls, giving them maximum waterproofness and robustness.
Terracotta pipes, used in vitruvian era to make water mains, were carefully sealed with lime mortar and cocciopesto made waterproof by mixing the dough with oil scum.
The author of the Ten Books appeared very distrustful of lead pipes, which accused of poisoning the water. He comparing this metal to the “cerussa” (that is, a lead carbonate) used at that time as a white pigment and found to be actually a powerful poison. On the other hand, starting from the last century, it was intended to give a strong demonstration of how human genius could dominate matter, to the point where, as Vicat says with worrying modernity, “exceed the natural rules at will” by indiscriminately introducing, in the productive process, those material that our ancestors would have undoubtedly banished, because they knew that culture, tradition and practice consolidated over thousands of years of experience could never have considered as friendship.

Cocciopesto (dough processing)
The most important indications for the handling of mortar made with cocciopesto are mostly found in the manuals of the eighteenth and nineteenth centuries. In fact, the oldest literature does not contain more than a few general prescriptions.
In general, manuals require long-dry mixing, ie without the addition of water, of the ingredients indicated by the recipes and then immediately use the made compounds.
In the nineteenth century, in particular, are recommended three methods of processing the above-mentioned materials.
The first one consisted in mixing, with the an iron hoe with a special head (called “capocchia”), on a lawn, the ingredients that had to make mortar, adding the amount of water needed to have the desired ductility.
The second way consisted in mixing the ingredients at dry, to which, only later, the water volume needed to reduce the mixture to a soft and workable paste was added.
Finally, the third way was to work with a hoe the mixture of lime and water in a mortar with surface covered with pitch, to which only afterwards the expected amount of cocciopesto or pozzolana was added.
At the beginning of the nineteenth century, instead of creating a slaked lime mortar, with sand, brick dust and the right amount of water, a fairly liquid compound was created in which to extinguish the lime that would only be added later.

Cocciopesto (plaster mortar, history)
The mortars with air lime and cocciopesto lime, ideal as exterior plasters and for tanks, are basically two, and vary in relation to the type of use and the function of the coating, the preparation or the finishing.
The two doughs can be summarized as follows:
1) lime blended mix, with cocciopesto screenings in various granulometry, depending on the use, tempered by additives and with the addition of sand (from quarry or river) as an inert to ensure that the dried product gives as secure resistance to contact.
2) lime-based dough, added with the result of crushing tiles or bricks reduced to powder or small flakes, large sand, and any additives.
The first dough reflects in its main ingredients the famous vitruvian recipe, in which 1/3 of brick fragments were added to the lime and sand mixture to obtain a mortar with particular hydraulic hardening characteristics.
The second dough, on the other hand, is recommended by the ancient sources for the construction of the inner lining of the tanks, as summed up by the classics of the end of 400 and repeated in the texts in the following centuries.
At every age the clumps of cocciopesto were obtained by the smashing of tiles, pots and bricks cooked at such a temperature as to exert in the dough the function not only of aggregates but also of pozzolanic reagents, ie of hydraulic artificial binders in which silica and alumina are still strongly active and interact with lime.
The use of “well-cooked” bricks, almost vitrified, would not provide the desired hydraulic qualities to mortar, because in this case the cocciopesto was reduced to a normal inorganic inert with mainly dye functions.
Many authors claim to use tiles in place of normal bricks because they are subjected, for their reduced thickness, to a more uniform baking.
Today’s research suggests that the greater pozzolanic reactivity of cocciopesto powder is found with the use of bricks or tiles, cooked at low temperatures: in the past such bricks were known as “albasi” that is, small bricks calcined at temperatures not exceeding 800 ° C.
The oldest sources, as already mentioned, report with some variants the Vitruvian composition. The most significant contribution is the 15th century. In the prescription it is advisable to add a third part of “antiqui tegoli”, that is old tiles, to the mixed lime with the sand, to obtain even more tenacious mortar. In the same sources it was recommended a compound where, in mortar and tiles powder, were added other materials include iron scales, to increase its hydraulicity, and a decoction of olm skins to make it probably more coherent and malleable, thanks to the tannin and sugars contained in that tree species.
The addition of dry oil (usually cooked linseed oil) is often recommended both in the dough phase and as a possible surface finish, probably to increase the plasticity and moisture resistance of mortars respectively. Linseed oil, in fact, being a drying oil, is essentially constituted by a mixture of unsaturated triglycerides which, if exposed to air, form a solid and transparent film.

The oldest texts of the fifteenth century recommend a plaster preparation suitable for ‘remedy to moisture’ on the walls for mural paintings, made with the overlapping of two layers of mortar with cocciopesto and linseed oil. The first layer was composed of brick grinding and linseed oil. For the same purpose, doughs made with cocciopesto and pitch or cocciopesto and vegetable resins were also advised.
Many authors have proposed doughs made from cocciopesto and linseed oil.
For example, it has been stated that it is possible to make a lime-based dough using linseed or walnut oil, sand or rubble, considered “impenetrable to water”.
Other significant variants, in the composition of mortars with cocciopesto, will be in the eighteenth century with the addition of quicklime to the base dough. Such doughs are generally recognized as mortars obtained using the “Loriot method”. Almost all the sources, starting from 1774, when the original French guy made its singular discovery, all manuals will insert the idea of Loriot in the chapters concerning mortars and then in those concerning mastics.
Loriot’s mortar had the “simple” peculiarity to be composed, as well as dry lime, river sand and cocciopesto, also of powder of quicklime.
The “Loriot method” was just another attempt to match the characteristics of the Roman age mortar. In fact, this method was derived from the interpretation that Mr. Loriot had given to the passage on the air lime of Naturalis Historia of Pliny, but it did not appear to be, in the end, up to expectations.
It was verified, in fact, that some plasterworks made by Loriot himself, after fifteen months of their realization, showed some vulnerability. They hardened very quickly – faster than a mortar with pozzolana – but underneath the hard surface, there was a compound with a consistency lower than that of a normal hydraulic mortar. The process described by Loriot was also too expensive since it required a quantity of lime practically double compared to a common mortar. In attempting to overcome this economic disadvantage, Mr Morveau proposed a variant of the Loriot dough, replacing the quicklime with ‘retread’ lime, or lime extinct in the air, and then baked in a specially designed oven in order to obtain still a lime definitely “reactive”.
It should be noted that the drawbacks of Loriot were probably derived from the fact that what he called “quicklime powder” (CaO) was in fact “calcium hydrate in powder” (Ca (OH) 2). Even Morveau had realized that quicklime exposed to the air hydrated quickly, falling in powder, due to the relative humidity of the air.
After these attempts, in all manuals, it was frequent to find indications of mortars were, in addition to cocciopesto and dry lime, also quicklime powder had to be added.
In a nineteenth-century manual, for example, there is a recipe for a mortar called “Perpetual Concrete or of the Fountains”, consisting of tiles powder, carbon powder, mixed with iron foam (Marogna – dross of fossil coal combustion) and pit lime, to which even quicklime powder was to be added. The resulting “cement”, albeit inferior to the traditional one, made with cocciopesto, was preferable to that made with just lime and sand, at least for damp places or for in water constructions.
Mortars made up with “Loriot method” (so were called the Morveau variants) had a quicker grip than normal mortars, but not the same duration; since the presence of non-hydrated calcium oxide was not excluded. The late hydration of the “bricks or mortars” in the mortar, caused a swelling of the mortar, causing a premature fall.
With the aim of obtaining compounds that had always “more quick grip”, some authors found it advisable to use soot melt in a mixture of water and orin, or powder of the same stone used to produce the lime. The latter solution, indeed, left a bit perplexed the most experienced artisans.

Cocciopesto (mortar for common beaten)
The indications concerning common beaten floors made with cocciopesto mortar are not very frequent: they are rather fragmentary and limited to the sources of the sixteenth century.
A first description of this type of floor, obtained by striking a layer of mortar containing lime and cocciopesto without stone clasts, is reported in the late 19th century classical literature, in which it was suggested, as it is convenient to make the floor harder and durable, to add 1/4 of travertine powder or pozzolana powder in the “classic” dosage.
It is also mentioned of the same kind of mortar in the following century, indeed, just as an ancient reference. Another interesting indication of this type of floors is found in the documents of the mid-16th century, which contains a recipe for the preparation of a water resistant enamel, containing, in addition to mortar with lime and tile powder , also iron scraps (Marogna, Maciaferro – see above) to increase its hydraulicity and a decoction of olm skins to improve its plasticity and probably to accelerate its grip.
The sixteenth-century indications, compared with those of the previous century, are more detailed and mainly refer to a sort of wrought-floor artifact, widespread especially in Lombardy and Venice.
Venetian Renaissance masters, who advise to add cinnabar to the dough, to color it, suggest that the object of the recipe is the so-called Venetian pastel, a type of floor spread in the Republic of the Doges of the sixteenth century and made with mortar containing cocciopesto, colored in dark red, mixing cinnabar to last layer dough .
The only “modern” indication on common beaten floor, is contained in the handbooks of the second half of the nineteenth century, describing a floor realized by the drawing of three successive slayers: the first is composed only of pebbles of a few centimeters in size; the second, for a thickness of 1.5 cm, of mortar with gravel and earthenware oddments; the third, finally, made of lime, fine sand and pozzolana of any origin.

Cocciopesto (Application Techniques) A “rendering” in cocciopesto for wet walls.
None of the sources studied by the G. Quarneti Documentation Center is exhaustive as far as drawing of plaster with cocciopesto is concerned; therefore we can assume that the practice of application was quite similar to the rule that governed the drawing of the common plaster of lime and sand.
Among the tips of the great Vitruvio, if the walls are subject to rising moisture, there is the suggestion to apply, instead of the usual layer of lime and sand (called “harenato”), thick coat plasterings in cocciopesto. He also suggests, for particularly humid places, to create an interspace and to roughen the inner surface with mortar containing pitted crumbs to further isolate the wall from water infiltration.
A further suggestion to improve the adhesion of plaster to stone or brick walls, is to previously whitewash it with lime milk, for the sake of creating a glue interface between the two surfaces. After it there should come the drafting of the plaster in cocciopesto.
Even from sources of 1400, it was suggested to use a mortar with quarry sand and bricks fragments of the size of “a few inches” for plaster layers closest to the wall surface, deliberately shredded to provide solid support to the following ones.

Mortar with Cocciopesto for water tanks
Suggestions for the construction of tanks, provided by the Author of the Ten Books, are handed down practically unchanged up to the authors of the 18th century. This is demonstrated by the fact that in a text of 1832, it is still suggested, for humid locations and for ground floor environments, the application of plaster, according to “Vitruvio’s suggestion”, consisting in mortar and powdered shreds.
For water-tanks and for all environments intended to contain water permanently, are recommended three layers of plaster, according to the example of the ancients. The first made of mortar with stone flakes; the second consists of lime mortar with of calcite and broken bricks (or pozzolana); the third, finally, consists of a thin layer of lime mortar with sieved fine dust of cocciopesto.
Teaching also includes a very important action: the freshly spread layer of mortar is to be carefully beaten with a metal tool, called “baculus”, which ensured to push to the surface all the moisture in the dough on the surface, thus preventing its damages in all internals.
To deny the modern and erroneous belief that the cocciopesto is waterproof and water-repellent on its own, on the last layer of the surface were applied abundant amounts of oil or animal fat to make the artifact impenetrable to water.

Laying of the Cocciopesto mortar
It is to be reminded to all who are going to re-make the lime plaster on old stone walls, that is worthless to wet the bricks with the intent of making new layers well stick.
The only removal of the old plaster layers is also insufficient: in fact, the original lime mortars, when applied, deeply penetrated into the pores of plastered bricks, occluding the vacuum with lime particles; the lime hydraulically reacted with the active substances that make up the bricks themselves, namely: (SiO2 + Al2O3 + Fe2O3).
If you want to get the same “chemical” and not “mechanical” effect of new lime plaster on bricks, it will be necessary to remove the occluding materials by energetic brushing, water jets, or delicate sand-blasting, so that the walls, subsequently wet, can recharge in their empty pores the water and the lime of the new mortars. Only in this way will you be assured that the plaster work will cause the same adhesion phenomena by hydraulic reaction that the previous mortars caused, at the time the first plaster was placed.
In the doubt, if you want to be sure that the new cocciopesto plasters, do not have to suffer the state of the walls when they are re-newed, it will be wise to change the lime with the mix of two different in nature: that is, you should mix together half of fat lime and half of lime-rich with marly limestone. The so prepared mortars make even quick grip on those walls that hold the moisture and give a sign that they never want to dry.
The plasterwork with cocciopesto so prepared and put into operation, well-beaten with the mallet, will adhere indissolubly to the walls and survive for ages undamaged. It is not uncommon to find, on the facades of our palaces, that the marbled coatings, completely destroyed by the insults of the time, have left naked and resistant cocciopesto plastering.
The researchers of the early nineteenth century pointedly but in vain tried to reveal the secret of the Roman mortals, trying to discover the mysterious matter that made them so tenacious and flexible.
Today the arcane is loose. The ingredient that provoked, and which still causes so much astonishment, is an element that can not absolutely be dominated by man, but to which man is subject: the time.
Here is why you never insist enough in defending the cobblestone terraces from the pike of the breakers: the restorative work of lime mortars and “cocciopesto” will never fully compensate for the qualities and characteristics of what has been destroyed.
Common fat lime, strong lime, hydraulic lime with cocciopesto, pozzolan, marogna, etc. all these are subjects show their real virtues in natural processes that need time, which, to our observation of modern men, appear very long. How can our modern hasty minds accept that “time” is the most important ingredient of our recipes? Just a century ago, Architect Giacomo Boni, in his “Imbellettata Venice, 1885”, already presaged the nasty and pernicious effects that “sad innovation” would bring to his beautiful city. The first awry attempts to simulate old plasters with broken tiles, with a mix of Portland and iron oxide, which would have to spill time and money to the deceived craftsman, must have let the sensible architect horrified, up to make him say that “That rotten stuff, trowel applied, festering strawberry or faded poppy coloured” could never compete in beauty and solidity with the lime plaster with blasted tiles, in that fine Venetian Gothic red: smooth, but not polished, that acquires with time beautiful brunette shades.
More, to those who precede the new cements by their strength it is to be said that these ancient plasters are so tenacious that, in order to scrape them, at gavel hits, it takes longer than necessary for the modern ones to fall alone.
In speaking of the processing of cocciopesto, however, one can not overlook one of the most peculiar surface finishing practices that in the past have admirably exploited the characteristics of the hydraulic binding reaction between lime and brick powder: the cso called “sagramatura”.

Beaten in Cocciopesto
The earliest sources attest that cocciopesto mortars, with or without sowing of colored stone clasts, were mainly used for the construction of continuous floors.
The floor made of grinding of bricks or tiles (earthenware in general) has in fact been recognized by many scholars as one of the oldest and most widely spread throughout the Mediterranean area.
The dough mixes with cocciopesto used for flooring are basically two
1) dough based on ditch fat lime with grindings of bricks or tiles, without sand, with any additives;
2) dough based on ditch lime, sand (of varying granulometry depending on the thickness of the layer to be prepared), fragments of earthenware material, of adequate size, and / or pozzolana.
The first kind of dough is the one described in the Vitruvian treatise, which, with small variations, remains, even in some eighteenth-century manuals.
The second, comprising sand, appears in classical literature for the first time in the late 1400s and is repeated in virtually all ancient sources, until it becomes a common constructive practice suggested in all nineteenth-century manuals.

Mortar for beaten with stone inserts
The most well-known beaten floors made with mortar with cocciopesto, described by the historical sources, is the “veneziana” or “terrazzo” beaten, which differs from what we commonly call beaten floor for the presence of more layers, in the last of which small marble flakes were arranged, according to pre-ordered drawings.
Venetian Renaissance architects find in the “Terrazzo” the floor described by Vitruvio, essentially reproducing the same succession of layers, and the same composition, varying the inert/lime ratio, in the last layer, in the size of 1 to 2, while the optimal one indicated by Vitruvio was 1 to 3.
In addition, the same Venetian architects provide valuable information on the materials needed for the construction of excellent “terrazzi” and advise in particular to use “Paduanian lime” instead of the well-known ditch fat lime. The “Padana” or “Albettone” (generally known as Albazzane) were recognized as limes with the distinct features of hydraulicity. Probably their use provided more quick hardening, higher resistance to contact and more quick and fast working.
Subsequent sources make some changes to these first indications, especially in relation to the number of layers and their composition. Lime dough (fat or hydraulic) and brick grindings thus enrich in some recipes with pozzolana and residues of marble processing.
In the second half of the nineteenth century, manuals recommend the application of three layers, the latter of which consists of only lime and marble powder. The same dough, for some authors, is enriched with pozzolana, probably to increase its hydraulic grip characteristics.

The Venetian Terrace (with lime binder)
The techniques used in the construction of the terraces vary according to the binder used. The lime-based construction technique is the oldest, therefore it requires more experience and is therefore the most expensive.
The types of terraces that can be built vary according to the thickness of the granulate, the chromatic variations of the marbles and the aesthetic effect created by the composition of the decorative motifs. A key ingredient in building the beaten terrace is the pebble lime.
The lime preferred by the terraces is obtained by low temperature (800 ° C) calcination of river cobblestone.
The construction of a terrace with slaked lime binder involves the following operational phases:
1. building the substrate
2. laying of the cover
3. expanse of the stabilization
4. sowing of granulation
5. rolling
6. beating
7. flattening
8. smoothing
9. grouting, seasoning and polishing
10. maintenance

GRANITE or PASTELLONE variants
Granite, or more precisely the granulated mixture, is a variant of the Venetian floor, where, while the bottom and the base-covering are made with classic ingredients and classic sections, the planting plan is not constituted by the stabilization but from a blanket on which a layer of dough of about 1.5 cm thick is spread, consisting of small granules and lime in a volumetric ratio of 1: 1. This roll is done by rolling and beating several times and by smoothing with a trowel. The small seed, which varies from 2 to 5 mm, allows for faster smoothing.
Laying this type of terrace requires special attention in the beating and rolling operations that need to be done accurately since the granite layer must be compacted with the underlying support layer to avoid the risk of granite disengaging during ageing process.
Generally, the classic marble granules used for the construction of the Venetian lime terraces are those obtained from relatively soft marbles for the purpose of being honed by hand. The types of marble used are the “Absolute Black” of Italy, the yellow Torri, and the yellow Verona, the red Verona, the white di Ciottolo, the “Biancone” from Verona, the “Bardiglio” and, in smaller quantities, breeds and arabesques in their different shades.
The oldest type of terrace, namely that since the 15th century has decorated Venetian homes thanks to the use of shades of hot and soft color, is called “Pastellone” and is constructed in a slightly different way from the traditional terrace. The Pastellone has a background made of cocciopesto and stone scrap mixed with pebbled lime. Unlike the terrace, the substrate or “solid”, constitutes the laying plane, not for the stabilization and for the sowing of the marble granulate, but for a layer of 1 or 2 cm thick of cocciopesto powder with rubble, mixed in equal parts and blended with slaked lime in a volumetric ratio of 3: 1. A final layer of dough is laid on this cover with a surface left appropriately rough. The dough is made of a mixture of granular marble powder, or milled brick powder, commonly known as “granziofina and lime” in a volumetric ratio of 1: 1.
The first hand is laid out with the aid of the tool with grafted a hard stone that moved backwards and forwards allows to forcefully spread the dough on the prepared rough. This dough spreading operation is performed twice; the third hand is applied with a paddle and the inert used is impalpable. During the preparation, the dough is worked with a small trowel and water, like a classic marmorino.
The traditional color of the “Pastellone” is red, originally obtained by inserting cinnabar red powder, extracted from a natural stone with a red vermilion colour, which was actually the only mercury sulphide ore found in various mines and in plentiful quantities. Today, the red “angeli” or the earth’s vermilion are used for staining. The red colour of Pastellone can vary depending either on the amount of dye used and on the type of brick powder being used.
Another classic colour for the Pastellone is yellow, which is obtained with the use of the pigment “terra di Siena”. There are also rare examples of green Pastellone that was obtained through the use of another green pigment called “terra verde di Treviso”.

THE SAGRAMATURA
The Sagramatura consists in the smoothing the obtained wall surface so as to create a subtle “tonachino” plaster (sometimes of a thickness of one tenth of a millimeter) covering the bricks on the exterior walls. The resulting effect is the formation of a covering layer with the colour of cocciopesto so that the opus testaceum loses all its shape of processing, though, especially when the worked wall is damp or wet, it traverses the underlying warp. There is no common technique on the application of sagramatura, the most used, however, is the one described in detail in the 19th century manuals: “In factories that are constantly exposed to seasons’ weather and excessive heat or cold, the best practice that can be used for plastering, Is the so-called ‘sagramatura’, but this can not be done diligently but in the walls built with new bricks. ”
As Alberti prescribes, after having perfectly erected the wall, with ‘repressed’ or ‘rotated’ bricks that were specifically cooked, to the surface was applied “best lime mixed with fine brick powder”, then, the the surface was rubbed with strength using a brick, keeping the wall always wet, to stir thin plaster and stick it in the porosity of the wall curtain.
This sagramatura work is to be continued without interruption up to when “you can count all the bricks that make up the wall”. The surface was then passed using the reverse edge of a well-sharpened trowel, so that it could be brought to “some smoothing and sheen”. Finally, in order to make the surface water-repellent, when the coating was well dry, two strong hands of cooked oil were passed over sagramatura..
In this regard, it is to be noted that not all the operators involved in the work of sagramatura had high wall made with new bricks from furnace suitable for such a sophisticated and laborious practice.
Often the wall was already existing and not entirely adequate to receive such a treatment: in that case the experienced mason dumped the wall with a medium-fine grain cocciopesto mortar and frowned in order to fill any superficial vacuum of the original mortars thus bringing the rugged bricks to flatness; the surface thus treated was left to dry and then abundantly wet again.
A thin covering of plaster was placed over it, but slightly thicker than an original sagramatura. The used mortar was pre-packed with well-seasoned ditch lime and sifted cocciopesto powder. When the plaster was still firm and not fully dry yet, it was vigorously smoothed with the reverse edge of the trowel until it was perfectly smooth. The result was such as to “hide the clear design of the brickwork, so that the surface appears as a continuous pinkish crosshatch” This way of plastering the bricks, with a smooth layer, is said “cappuccino”.
There are archive documents that tell about red-painted cappuccino plasters, so that the surfaces “smoothed & painted & reddish, seemed made of new bricks” (1449).
Even though in the nineteenth century there were manuals to teach about the canonical application of the sagramatura, this technique was practically done almost only at the “cappuccino” and if “the compactness and the uniformity of the color given by sagramatura” were missing, the plaster could be washed with “colored water and colored earths” to gain in “equality and freshness”.

Notes from the workshop
The “cappuccino” plaster consists in a shaving of 40 pieces of lime dough with 60 parts (in volume) of impalpable well-sifted cocciopesto powder. The plaster should be applied using the edge of the trowel or with a squared spatula, such as a common marmorino, over a base of rough cocciopesto mortar. A variant suggests that the plaster can be strengthened using strong lime in natural color. You can add to the dough a bit of “Bruno di Marte” pigment to make uniform the color of the dried plaster.
The cappuccino plaster should always be protected with abundant oil or wax brushstrokes.
Historically, for cappuccino stucco, it means any smooth (but not glossy) thin plaster directly applied to the wall, without the prior drawing of the background plaster. The peculiar feature of this latter version is the imperfect planarity of the work, on which the uncertain warp of the underlying brick surface emerges.
Otherwise, if the plaster was made up of fat lime and powder of white carbonate and the surface was drawn straight, smooth and polished with soap or wax, in this case the work would be called “Marmorina”.
The “Marmorina” is made up of several layers: whose the granulometry goes from the coarsest to the finest, passing from layer to layer. When finished the “Marmorina” reaches the thickness of 1 – 1.5 cm; the “Cappuccino” instead is more economically limited to 1 – 2 mm, in two passes: here is the reason why it is said “cappuccino”.

The Terrazzo flooring

The Terrazzo flooring with polychrome marble sowing on the floor are the result of a complex constructive process that consists in overlapping layers with different thickness, composition and function.
The main phases of the construction of the Terrace with beaten floor coincide with the ones reported in the oldest notes regarding the construction of floors where the mortar with cocciopesto is the main component of the layers that make up the flooring. The indications differ, however, with respect to the name given to each layer, its operations, surface working and finishes.
After the preparation of the first layer composed of pieces of earthenware and lime, made with the shovel and then draw with an iron tip rake, it is necessary to wait a rest period of several days, depending on the season, before the beating.
The craftsman, with two long irons tools, called “zanche”, proceeded to fasten the first layer of mortar parallel to the walls in opposite directions in alternate days. A regular force was imprinted at the zanca, leaving at least one day between a beating and the next, which should always take place in cross direction with respect to the previous one.
The beating had to continue until the lime dough appeared on the surface. This first phase could be considered complete when the mortar layer, if beaten again, was so compact that it did not indicate that could be further compacted.
Upon completion of the first beating operation on the first layer, it was slightly beveled by “cracking” the surface with the pike or the hammer pen – to facilitate the clamping of the next layer. Than a second one was spread and possibly a third, made with lime, cocciopesto (or pozzolana) and marble powder in equal parts, repeating the compaction operations with the “zanche”. In the case of the last layer, it was necessary to trace the decorative sketches on the firm mortar, but not yet completely dry.
The preparation of decorative patterns could take place in two ways:
the first one included the reproduction of the drawing on large perforated cartons, from which the drawings were transferred to the background with the dusting technique, as is done in the fresco.
With the second method, the contours of the drawing were instead reproduced directly on the surface with a pointed iron, like a sinopia.
After finishing the seeding in the various compartments, the masters agree on the rolling operation by means of a stone (or iron) cylinder used to convey the tiles in the mortar until almost sinking them into the surface. Then, after rolling the bottom several times, the beating was repeated with the metal zanca.
Than the work was suspended for a few days, before proceeding to the actual smoothing step.
The finishing process took place in two distinct phases:

1) A first wet sand smoothing step, obtained by rubbing the surface spread with mixed water and granular sand or pumice stone powder, with a tool, consisting in a sandstone drawn by ropes, or with a handle according to different texts;
2) A second dry smoothing step followed to eliminate any irregularities, carried out with the same tool as before in which the abrasive stone was replaced with a finer grain that was rubbed on the floor covered with just thin sand. This abrasive sand for some terraces had to be sea sand, others prefer pumice stone dust.

After passing the tool for smoothing, before polishing, it was used to underline the contours of the picture with a steel tip and then to fill the noticeable.
The next polishing took place by soaking the surface, on alternate days, with linseed oil, to be apply, or using a trowel or more simply with a soft cloth.
After a day of rest the floor was covered with sawdust and finally cleaned.
The decorative garnishments were highlighted, if necessary, spreading mixed lime and colors.
After 6-8 months, the colored mixes were wiped with a sandstone and polished with raw linseed oil and soap melted in boiling water. The polishing had to be carried out with woolen cloths and repeated three times, in the last of which it was necessary to use “well-boiling” oil mixed with wax.
To keep the terrace always shiny and protected, the “Rule” recommended to repeat polishing with oil every two months.
For the maintenance of the terrace, it was suggested to use one of two methods: one hot and one cold, for “arranging a broken terrace’.
The first consisted in the application on the terrace to be “restored”, of a compound containing “bolo armeno” (a reddish clay) and cocciopesto, to be laid with a hot iron.
The second one seems to refer to how to reconstruct the missing decorated parts.
The reconstructed “stone”, with the suitable color, was then placed on the terrace with a mastic composition made of warm oil, cheese glue, marble powder, egg-white and lime.
The “ammattonati”, ie bricks placed edgewise or flatwise, according to Vitruvio and the Renaissance classics, were displaced by all artisans, on a layer of mortar of varying thickness.
On the bottom layer (statumen) was spread a first layer of mortar made up of lime, stone clusters, and large size debris of tiles or bricks (rudus) and then a second one, that had to hold the floor, containing lime and cocciopesto of smaller size (nucleus).

If the flooring was intended for outside, between the two layers, it was proper to insert a layer of tiles, for a size of about 40 cm, with the fillets filled with lime and oiled with oil or animal fat.
For each of these layers, the prescriptions of the past suggested an energetic beating with sledgehammers. After the laying and the beating of the floor there was the phase of smoothing done using a whetstone.
In the sixteenth century, instead, it is referred to as a “very famous thing” a sanding process consisting of a first phase of abrasion performed using granular sand and water and a second one with “Tripoli stone” powder. The process was completed spreading up abundant of walnut oil.

Cocciopesto (laying mortar for brick floors)
Even in the case of the use of mortar with cocciopesto, as a laying mortar for other types of flooring, the source information is chronologically limited to the older ones that almost match Vitruvio’s instructions.
In the Vitruvian treatise, the mortars with cocciopesto appear to be a compound of dual use: as plating mortars for flooring made up of large lithic fragments arranged in geometric shapes, or for “ammattonati” (floors obtained by laying bricks), or as mortars that became, if appropriately beaten and polished, the surface layer of the floor itself.
The use of mortar containing lime and cocciopesto was recommended in the penultimate layer (nucleus) and in the first one (statumen) in order to prevent possible damaging water infiltration without increasing the thickness of the floor.
The only manuals reporting few synthetic information on the handling of cocciopesto doughs for horizontal coatings are from nineteenth-century authors, who advise to obtain the right composition of the compound with a long and prolonged stirring without using any water other than the strictly necessary one for the dough of the ingredients, adding, if necessary, to soften the mortar, a weighted amount of lime in rather liquid paste.
Some differences can be noticed on the technique of preparing the first layer of mortar, which would have to contain a lot of water and have a hard and “milky” consistency. The mortar of the second layer, on the other hand, had to be soft and ‘very handled’. The third, finally, had to be “liquid rather than hard”.
Nowadays, the “Terrazzista” ( the craftsman expert in making terraces) skill is crucial, mainly to avoid cracking in the floor.

Pozzolana

In nature there exist materials (pozzolane, Santorino, Trass, Gaize) which contain silica and alumina under the same conditions as they are found in the marly limestone after cooking, therefore these natural products when mixed and knead with hydroxide of calcium, become hydraulic mortars.
The use of these natural materials dates back to the later epoch.
It is established that the volcanic earth on the island of Santorini was already used in VII century BC. to make water-resistant lime mortars for tank cladding. Even the Etruscans already knew the properties of such earth, which they used for underwater constructions.
However, these materials did develop remarkably in marine structures building in a later epoch, during the Roman period, which strengthened this technique with the repeated practice of preparing hydraulic mortars, and the widespread use of the pozzolane in the Neapolitan area and in the Lazio volcanic areas. It is right from the location where the first Roman pits, near Pozzuoli, were located, that derives the ancient name “pulvis puteolanus”, and hence the Italian name “pozzolana”.
Vitruvio, in his “De Architectura”, announces the “pozzolana” fields in Naples, located “in the vicinity of bay and in the vicinity of the township close to Vesuvius” and describes the hydraulic properties given by these materials to mortars, in which they are blended with lime and crushed stone: “mixed with lime and stone is not only makes strong every kind of construction, but especially those that are done in the sea, they become solid substances.”
In the same work, in Chapter XII of Book V, Vitruvio still refers to pozzolane phlegree, which come “from Cuma to the Temple of Minerva”, indicating the right proportions to be used between pozzolana and lime: proportions that are fixed in three parts of pozzolana and one of lime, which is the ratio still used today. Finally, he gives instructions on how to prepare the mix between mortars and crushed stone to form concrete, that was made up of large pieces of stone immersed in the Pozzolanic mortar.
The remains of numerous underwater works of great magnitude have come to us to testify the truly high degree achieved by the Roman construction technique. We can mention among the most important the bridges Fabricio, Elio, and Milvo and the port works of Ostia; the Traiano pier in Civitavecchia and the port of Nerone in Anzio, which after about twenty centuries of diving in river and marine waters, still retain excellent mechanical strength.
These hydraulic mortars, based on pozzolana and the like, were the only ones used up to the end of the eighteenth century and the beginning of the nineteenth century, and in spite of the rapid development of today’s production of modern cements, they still retain all their value and their stunning strength, especially in marine constructions.
The most prestigious engineering work of antiquity is the Pantheon in Rome. On this stunning monument, devoted to all the gods, insists a monolithic dome, done with lightweight concrete, whose diameter reaches the incredible size of 43.3 meters.
Before this work was erected, no one had ever dared to think of designing a structure of this boldness. Neither the majestic dome of Hagia Sophia (about 33 meters), nor the dome of St. Peter (about 42 meters) despite their grandeur, show the genius of those who designed it and the ability of those who built it, which can be overcome only in our times thanks to the construction technique of reinforced concrete. How did the Romans come up to such prestigious works?
It was the use of Opus Caementitium, which allowed so much beauty. The shape of the element to be constructed was obtained by means of a formwork made of appropriately laid stones or made of wood boards and beams. Blends were thoroughly and prolonged mixed with mortar and with the hardening the binder and its maturation, was obtained a conglomerate very resistant to compression. The wooden formwork was then removed, as it is today, to be re-used. The term Opus Caementitium indicates both the technique and the quality of the product. The term can therefore be translated as “concrete construction” or more generally “Roman concrete” (see also “materia saracinesca” in the Bellum Goticum of Procopio from Cesarea).
Originally, the Roman concrete preparation technique developed to contain the the previously huge expenses and to offer more quick solutions for the construction of city walls, barns, watercourses, port facilities, aqueducts, and more. From the middle of the first century AD, with the refinement of the Opus Caementitium technique, skilled architects invented new design strategies in using this material for the construction of vaults and cupolas.
It is amazing to find out how Roman engineers have already experienced the principle of modern reinforced concrete.
In a hypocaust that was provided as usual with hot water through the pipes, the most important thing is that in the coverage of one of these canals, made in Opus Caementitium, archaeologists found iron reinforcement drown in the conglomerate. Have also been found iron reinforced mesh in the roofs of the Herculaneum and in the Baths of Trajan in Rome.
Investigations on the mechanical strength of this material have been carried out, by investigating specimens from Roman historical structures throughout Europe, drawn from artifacts belonging to the most common types of constructions such as masonry and walls, foundations of columns, roofs, water preserves and pipelines. The results of the survey lead to a surprising conclusion: the compressive strength values of the various Opus Caementitium are between about 50 and 400 Kg / cm2. They, therefore, overlap, in order of magnitude, the values of resistance of a concrete of our times. But what is most surprising is that the choice of the granulometry of the inert was scrupulous according to similar criteria as ours. From the reconstruction of two original granulometric curves, it can be seen how these could perfectly meet the current normative requirements.
The starting mineral for the preparation of an Opus Caementitum is essentially the same as today used for the production of cement and fat lime. Lime and aggregates were added to pozzolanic compounds such as volcanic tufa and sand obtained by grinding bricks (cocciopesto). The concrete was cast into layers: the repeated beating and constipation of the material allowed a uniform transmission of the load to the structure, and due to the equal grip between layers, obtained by compaction, a single body was obtained, with properties comparable to those of a stone.
It can be argued that the technique for preparing Opus Caementitium has played a crucial role for the secular stability of the Roman Empire, and the durability of these works, which we can still admire, are an evidence of rare constructive abilities. More than the outrage of time it was the man to be pitiless: ancient monuments, you know, have always been privileged stone quarries for the new ones. But what remains of most precious about opus caementitium, that was a topic of study for many researches in the eighteenth century, is the wise use that the Romans learned to do of the pozzolana.
It is enough to remember that from 1740 to 1760, the Superintendent to the waters and rivers of the Republic of Venice, Bernardino Mandrini, designed and started the initial works of that pharaonic work of defense of the lagoon city, called “the Murazzi”. The boulders barrier, which can still be admired today, was completed at the rate of 80 perches (about 160 meters) per year, walling up underwater boulders with lime and pozzolana mortar. The Mandrini died in 1747 without seeing the work accomplished.
The Pozzolane are ashes or volcanic ejectyions, modified by time and weathering agents: they are composed of silica, alumina, iron oxide, lime, magnesium, potassium, sodium and other elements in very small quantities; It is more or less multiple basic silicates.
Regarding the formation process, that is, regarding the so-called pozzolanic genesis, opinions are incompatible: according to Michaelis (1899), the active part of the trass (pozzolana chemical name) would be the decomposition product of minerals that underwent the action of water rich in carbon dioxide and in overheated water vapor.

According to G. Gallus (1908-1909), however, the pozzolane derive from materials removed by volcanic eruptions from deep geological layers of essentially clay composition, materials that during the eruption must have undergone sufficient calcination to determine a deep chemical dehydration of the mass, without, however, being completely brought to the melting state, as is the case for crystalline parts. Once deposited, the atmospheric agents intervened for many centuries on these materials, causing a slow and progressive modification of silica and alumina, already in the free state; modification which consists essentially in an intimate hydration of the individual particles, so that getting in touch with the lime , they are in appropriate conditions for allowing the phenomena that determine the hydraulic grip.
To this regard, it should be added that, according to Parravano and Caglioti (1937), the active part of the pozzolane would be an aerogel having the nature of a dissected silicagel and resulting from the spraying of magma in fusion under the action of air and overheated steam
to.

Evaluation of Pozzolanic activity
It was the aforementioned Prof. G. Gallo who first thought of applying the polarizing microscope to the study of the pozzolane to monitor for about an year the phenomenon of the hydraulic grip of the same ones in contact with the calcium hydroxide.
It was thus possible to observe that the various pozzolane are composed of various crystalline elements, such as augite, mica, leucite, sanidino, waste fragments, and so on. Together with these elements, which do not take part in the gripping phenomenon of the mortar, there is a granular and amorphous mass, the more reactive, the more it is present in abundance in the pozzolana; this mass that has the property to strongly swell for the action of the lime, resulting in a significant gelatinous flocculation, which is a sign of hydraulic reactivity.
It was thus possible to observe that at first the gelatinous flakes of the pozzolana, intersecting in all directions, gave rise to a compact and waterproof mass within which, after about two months, hexagonal crystals were deposited; these, in the analysis, were made of hydrate calcium aluminate, which evidently precipitates from the saturated solution with the presence of excess lime, whose raw formula is:
Al2O3. 3CaO. 10H2O
From all of these research it can be concluded that the granular and amorphous part of the pozzolane which is the active part, is made up of silica and alumina in such conditions that can react with the lime, forming a gel within which small crystals deposit causing the hardening, while a strong layer of CaCO3 is formed on the surface.

About artificial pozzolane
In the regions missing natural puddles or, in any case, missing pozzolanic materials, since a century, it has been attempted to produce artificial pozzolane. The most widespread type in the common use of these pozzolane-like artificial materials is the one obtained with suitable clay roasting.
Above 800 ° C, the mass obtained from clay cooking is the one formed by amorphous silica (derived from kaolin), crystalline silica, alumina, and when present, also by alkali CaO, MgO, Fe2O3, etc.
At higher temperatures the different oxides begin to blend with silica, forming complex silicates: alumina provides mullite, i.e. 2SiO2. 3Al2O3, while other oxides form silicates which at higher temperatures melt, giving a glassy mass incorporating mullite crystals.
Different constitution clays gives rise to products with different technical properties.
In fact, a clay with predominant kaolin formation loses water at 450 ° C; Dehydration then completes at 600-700 ° C with a simultaneous complete reconstruction of the crystalline lattice.
Different is the behavior of a montmorillonite clay (bentonite). The montmorillonite group is characterized by the different combination state of the contained water, of which a good part, unlike for the kaolin, is loosely bound to the lattice and is eliminated at a low temperature (between 50 and 200 ° C) without that the lattice undergoes sensitive changes.
This different state of aggregation significantly affects the reaction of the clay materials with the lime, thus differentiating them with respect to the obtained reacting artificial pozzolane. It is admitted that in the kaolinite the heating above 550 ° C releases silica and alumina in a state of extreme division, which can react with the calcium lime forming silicate and aluminates of hydrated calcium.
As pointed out by Santarelli (1942), the materials made up of montmorillonite behave differently from the first, because they can fix lime in the natural state. Once baked at 700 ° C, and mixed with water, they provide mortars with remarkable mechanical strength.
Some pozzolanic behavior is also present in some types of amorphous silica, resulting from the destruction of trachytic rocks by action of water or acid gases, and residual silica from the leucite processing. (Leucite is a potassium and aluminum metasilicate, colorless or whitish (KAl / SiO3) 2, with specific weight 2.5 that is frequently found as a constituent of many eruptive rocks in lamellar form. From it potassium can be extracted.)
Analogous behavior have the fossil meals, made from skeletons of diatoms, and formed of hydrated silica with a high specific surface.

The tuff
Rock, usually not very compact, derived from the cementation of pyroclastic materials, that is, debris products thrown into the air by volcanic craters. These pyroclastic materials are of direct magmatic origin, but since they are deposited by natural fluid media such as air or water, the resulting rocks are considered sedimentary.
In fact, after the first stage, the alteration, pyroclastic materials are subject to all the other stages typical of the sedimentary process, such as transport by wind, sedimentation, directly from the air or later in the marine environment, and diagenesis, mainly for compaction and cementation, before turning into a more or less coherent state.
Volcanic projectiles are very variable in size and have been classified as bombs and blocks over 32 mm in diameter, lapilli between 4 mm and 32 mm, and ashes below 4 mm.
As with common clastic rocks, even for pyroclastic ones, it is used to distinguish rocks from predominantly coarse and finer materials.
The former can be further subdivided into agglomerations and volcanic breccias depending on the rounded shape of the constituents. In agglomerations the rounding is high because they are volcanic bombs solidified during air transport, while the breccias show a smaller rounding because they are formed from already solid blocks at the time of the explosion.

Stones properly referred as tuffs, are the sandstone correspondents and consist of ashes and lapilli more or less cemented. As in sandstones, constituents can be rock fragments (lavas contemporary or antecedent to the explosions, or rocks of other origin) or granules of individual minerals (pyroclastic or not), but there may also be, and are sometimes predominantly, glass fragments, that is, fragments of non-crystallized lava. Exactly this highly unstable vitreous fraction is susceptible to devitrification, resulting in the formation of crystalline, often clay-like montmorillonite material.
The composition of tuffs is obviously different depending on the nature of the original magma: there will be riolithic, trachitic, basaltic tuffs, etc., identifiable by fragments of lava and minerals possibly present.
In Italy there are huge tuff outcrops: the sites are evidently related to the ancestral volcanic structures. Thus, the largest extension lies in Lazio, around the ancient volcanoes (today as many lakes) of Bolsena, Vico, Bracciano and Albano and in Campania around Roccamonfina, Vesuvius and the Phlegrean Fields. Minor extensions can be found in Lucania, around the Vulture, in Sicily, in the Iblei Mountains and in Northwest Sardinia.

Pozzolana is just from Pozzuoli?
“Pozzolana” stands for any material that reveals pozzolanic activity. And for Pozzolanic activity is meant the complex reactive phenomena which, in reasonable times, at ordinary temperature and pressure, and through properly hydraulic gripping and hardening phenomena, transform doughs of lime (Ca (OH) 2), “pozzolana” and water, in a compact material, with stone appearance and characteristics.
All the “pozzolane” (both natural and artificial) have a high hydrated silica (SiO2) content, and are mainly composed of glassy or amorphous components. The existence of these structures, however, is not a necessary condition for the appearance of pozzolanic properties, as there are other pozzolane, such as the tuffs, rich of zeolite minerals, which have a different predominantly crystalline structure.
The basic characteristics of the “pozzolane” are two:
a) ability to react with calcium hydrate (Ca (OH) 2);
b) ability to form products with binding properties..
The pozzolane can be natural or artificial.
Natural pozzolane: among these the most common are of volcanic origin (trachitic, pyroclastic rocks), coherent: compact materials such as tuffs, conglomerates (see trass), and incoherent.
To incoherent materials belong the typical Italian pozzolane from the regions of Campania and Latium together with the so-called “Santorino land”, which is a very little coherent tuff, but with the highest content of active hydrate silicate (69%).
Among the compact materials there are the German trasses (the most typical pozzolanic tuff) known and used for their Pozzolanic qualities since Roman times, the “Neapolitan yellow tuff” and the tuffs of the volcanic region of Lazio. All of these have a zeolite matrix.
Artificial pozzolane: these are materials that have acquired a pozzolanic character due to appropriate thermal treatments that have transformed their primitive nature.
a) The Clay. Clay minerals, cooked at temperatures between 600 and 900 ° C and grinded to the fineness of the sand, show a clear pozzolanic activity.
Given their origin these pozzolane are essentially composed of silica and alumina.
b) Flying ash. Flying ash consists of finely parted ashes produced in the combustion of pulverized coal in thermoelectric plants and collected by mechanical gatherers. Due to the high temperature reached in the instantaneous combustion of coal, the mineral part contained in it, mostly blends and produces small droplets of molten mass, which in the subsequent abrupt cooling are transformed into glassy particles.
c) AOther materials. There are some materials that contain varying amounts of clay. These materials possess an appreciable pozzolanic activity: however, subjecting them to heat treatment, the pozzolanic characteristics improve as the clay fraction is decomposed and activated.
The composition of the pozzolane varies, especially for natural ones, from pozzolan to pozzolan.
However, on average, its composition is as follows:
SiO2 45 ‑ 52%
Al2O3 15 ‑ 23%
Fe2O3 6 ‑ 12%
CaO 3 ‑ 9%
MgO 1 ‑ 4%
NaO+K2O 3 ‑ 13%
The hydraulic properties of a pozzolana are measured by determining its reactivity with lime. Accordingly, the pozzolane are classified as active and weak. Active pozzolane have more pronounced hydraulic properties, these harden and provide products with more mechanical strength. This strong attitude to react with lime depends not so much on the chemical composition of the pozzolana, but on its structure.

Steel artificial hydraulic limes.
If blast furnace slags are added to the lime instead of the pozzolana, in an appropriate mix ratio, a hydraulic binder can be obtained with mechanical characteristics close to those of mainly hydraulic limes, having chemical resistance equal to the pozzolanic hydraulic lime. Blast furnace slags are an important byproduct in cast iron production. They are essentially silica, alumina, and calcium oxide. The chemical composition of the slag is very variable. On the average it is:
CaO 43 ‑ 50%
SiO2 26 ‑ 32%
Al2O3 12 ‑ 20%
MgO 4 ‑ 6%
At the egress of the furnace slags is granulated, ie hardened by abrupt cooling in water and made granular, with grains of about 1 to about 5 mm.
Furnace slag is in itself a hydraulic binder. However, its hydraulic properties must be activated by the addition of an even small quantity of alkaline substance, such as calcium hydroxide (Ca (OH) 2), which ignites the hydration of the slag.
It is to be noted the difference between the pozzolana and the furnace slag: the former is not a binder in itself but forms a binder if mixed with lime; on the other hand, the high furnace slag is a true hydraulic binder, as it can harden when mixed with water, provided that you awaken its hydraulic properties with a suitable activator.
The use of hydraulic limes is generally limited to the preparation of mortars replacing the aerial ones, when higher resistances are required, or in the presence of wet walls or deep mortars in an asphyxic environment.
Their hardening is partly due to the formation of calcium carbonate for hydrate-carbonation (Ca (OH) 2 + CO2 – H2O), and partly to the hydration of aluminized silicates and calcium ferrite present in the formation of the gel as we’ll see later.
As mentioned above, natural pozzolane are the ones derived directly from the deposits that are found at the volcanoes; artificial, on the other hand, are the ones that can be obtained by burning some substances that are liable to acquire hydraulic properties typical of the pozzolane.
The weight of the pozzolane varies according to their origin and quality.
For the natural ones of Italy it may be considered to oscillate between 1157 and 1228 Kg / m3. Their color has varying degrees, being whitish, black, yellow, gray, reddish, brownish, and violet. In the neighborhood of Rome you can find reddish-brown and violet ones (Tivoli); those from Bacoli, near Pozzuoli, are bigie; at Torre Annunziata you can find rather black ones; tending to the red, the ones from Mount Paternò in Sicily, and dark gray – tending to the gloom – the ones found on Monterosso.
It has always been unjustly assumed that the quality of the pozzolana is better, the more intense it is the color. If so, the best should be the ones from Rome (S.Paolo) and in descending order those from Bacoli, Torre Annunziata and Monte Paternò. But it’s not like this. What makes a pozzolana of the best quality, is essentially the highest percentage of silica contained therein, in spite of the more or less brilliant color of the matter.
In fact, Santorini, though having a blackish color that is far from captivating, has a pozzolanic reactivity with lime hydrate, which has no equal in the world.
In addition to the aforementioned pozzolana’s qualities, some siliceous arenas having a small amount of pozzolanic properties are used as pozzolane, if used in the natural state, and which have a fairly good degree of pozzolanicity when they are lightly burned. There are deposits of these pozzolanic arenas at Brest and in Lower Brittany.
In this regard, some experts come up with the doubt that some plasters, made up of fat lime and thin silica sand, put into operation by the great Andrea Palladio, and that the investigation shows to be much more strong than other manufactures of the same period made up of powder of Marble, are actually plasters with burned siliceous sand coming from Murano glassworks, where the Architect found some materials for his work.

Certainly it is known that a master glassmaker, friend of Palladio, provided the latter with the glass powder to prepare the marmorini with which to decorate the columns of the Rotonda in Vicenza. From other sources it can be seen that Santorino’s pozzolana was also widely used in the construction of the foundations of the Venetian and Trieste palaces, and the Rhine Valley trasses, reduced to dust and sifted, have been widely used (and still are ) as pozzlane in Germany.
Good artificial pozzolane can be obtained by calcining the clays in the state of dust and the quality of the pozzolane thus obtained depends essentially and directly on the silica fraction contained in the clay earth and on the degree of their burning.
Sometimes it is convenient to calcinate powdered clay with a quantity of slaked lime also in powder form: a mixture of 1 to 3 parts of lime with 7 to 9 parts of clay, conveniently mixed and calcined, gives a good lime with pozzolanic virtues.
The burned and crushed bricks are also suitable for the preparation of artificial pozzolanic mortars, with a composition identical to that of volcanic ones. The substance obtained by reducing the bricks is known with the name of cocciopesto, which can be of great or small size depending on the sieve used. The best quality of cocciopesto is the one that comes from the medium burned bricks, but in general, the best result in the preparation of cocciopesto, can be obtained using tiles and in general bricks with a small thickness, like all those evidencing a more uniform degree of cooking.
Also basalt, which is a hard volcanic rock, baked and then crushed in powder, also gives a good artificial pozzolana.
Vicat notes that, as well as the basalt, even ferruginous gres, similarly treated, gives products with significant pozzolanic properties.
Indeed, the goodness of these surrogates can not overcome the connaturated energy of natural pozzolane.
Even fossil or vegetable ash, mixed with slaked lime either fat or lean, makes mortar slightly hydraulic; this, moreover, explains how the residues of lime kilns (ash with live lime crumbs) mixed with water behave like hydraulic mortars.
In the North-Africa Maghrebs and in the whole eastern Mediterranean basin, it is still in use to knead the lime with part of the ash of the fuel used to calcinate it.

About the Pozzolanic Mortar
When you want to get a hydraulic binder, to make masonry mortar, add natural (or artificial) pozzolana to the putty, in the following proportions:
A piece of putty for four parts of a pozzolana.
For the lime that has to be used to make mortar for plaster, it is advisable to reduce the amount of pozzolana and use the ratio:
one volume of putty and three of the pozzolana.
If starting from powdered hydrated lime, the dosage becomes:
100 Kg of hydrated lime for 1 m3 of pozzolana, for masonry mortars;

There should be much more to say about building materials used in antiquity, among other things those also correspond in part to the materials used for bio-building, but we have limited ourselves to returning the features of the main products

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