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
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
9. grouting, seasoning and polishing
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 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”.