Old buildings: rediscovering "Cocciopesto"
An ancient and current material for the renovation and rehabilitation of historic buildings
In modern times, the use of lime has been supplanted by the use of cement, because it is easier to apply and at a lower cost with good mechanical properties.
Compared to lime, however, cement deteriorates in the presence of salts and acid rain; moreover, it carries moisture inside walls leading to their gradual disintegration. Precisely because of these negative aspects of cement, some more careful applicators have progressively reintroduced lime, studying and refining ancient techniques, so gradually the use of lime (which is expressly required in archaeological and historical restoration) has gradually expanded in green building work.
Lime is obtained from the firing of carbonate rocks whose composition influences the quality of the final product. Lime is divided into two main categories; aerial lime and hydraulic lime. Aerial lime is so called because it hardens over time due to carbon dioxide in the air. During the firing process (known as calcination) at about 900°, the calcium carbonate present in limestone rocks (CaCO3) dissociates into carbon dioxide (CO2), which volatilizes and CaO-calcium oxide or LIVED Lime. If quicklime comes into contact with water, the water molecule (H2O) aggregates with the lime oxide molecule (CaO) giving rise to lime hydroxide (Ca(OH)2) also called QUENCHED Lime by the phenomenon known as quenching. Extinguishing is an instantaneous and exothermic phenomenon with enormous heat development (278Kcal per kg of CaO) and an increase in volume of about 50 percent. This procedure, performed by the ancients, is very dangerous for the safety of the operator, so today's regulations prevent the lime from being extinguished by the worker on the construction site, as was the case until a few decades ago, in the absence of adequate safety conditions.
From the slaking of lime, hydrated lime is obtained in powder form, or by allowing it to mature for a long time in water, slaked lime is obtained ( by separation of the fatty part that settles at the bottom from the water that rises to the surface).
NATURAL HYDRAULIC LIME
Natural hydraulic lime has hydraulic properties: it hardens in the presence of water.
Steps in the production of natural hydraulic lime (abbreviation NHL).
- Firing up to 900°C of a marl that also contains clay-limestone fractions.
- Quenching and grinding
- During firing at 500°C, clay (xSiO2 yAl2O3 zH2O) decomposes into silica and alumina (xSiO2 + yAlO3 + zH2O)
- During firing at 900°C, limestone (CaCO3) decomposes into calcium oxide also called quicklime (CaO) and carbon dioxide (CO2)
- Carbon dioxide is a gas and is dispersed into the atmosphere.
- Hydraulicity comes from silicates, calcium aluminates, and aluminum oxides, not combined, which react with the lime hydroxide obtained after quenching.
Artificial hydraulic lime production (initials HL and FI).
Artificial hydraulic lime, a modern product, is made by mixing other hydraulic binders such as cement , or blast furnace slag, with lime. Regulations impose different acronyms so that consumers are able to understand the different quality and environmental performance of what they are buying.
The starting point for making a good lime mortar is the choice of binder Historically, in the Mediterranean area the binder used was quicklime and slaked lime, and the component added to lime to make mortars that were particularly resistant to water and wear and tear were volcanic dust (natural pozzolan) and ground crock(artificial pozzolan).
By pozzolana is meant any material that reveals pozzolanic activity, and by pozzolanic activity is meant that complex of reactive phenomena that transforms mixtures of lime, "pozzolana" and water into a compact material through properly hydraulic setting and hardening phenomena.
Pozzolans are clay minerals that have transformed their primitive nature through strong temperature elevation either naturally during volcanic phenomena or artificially through firing at temperatures between 600and 900 degrees and subsequent fine grinding.
Clay is a sedimentary rock composed mainly of hydrated aluminum silicates (xAl2O3.ySiO2.zH2). It may also contain non-silicate materials such as calcium carbonate, iron carbonate, etc. At 900°C, calcium carbonate(CaCO3) breaks down into calcium oxide (CaO and carbon dioxide(CO2); carbon dioxide is a gas and is dispersed into the atmosphere, cacio carbonate reacts with silica and alumina produced by the dissociation of clay, resulting in compounds such as calcium silicate and calcium aluminates during hydration, which are very reactive materials against lime, increasing the strength of the plaster.
This plaster made from slaked lime and ground terracotta powder is called cocciopesto.
2. THE COCCIOPESTO.
Cocciopesto is the material characterized by the best state of preservation among those found in historic buildings, and in archaeological excavations in Roman times we find the first writings that speak of lime and pozzolan or lime and cocciopesto: this new mixture had the ability to resist wear and tear and harden faster even in water. In the harbors, in contact with seawater, the structures became stronger and stronger as time passed.
Pliny the Elder, in his Naturalis Historia (77 AD) thus states "impregnable to sea waves and each day stronger than the day before." A group of geologists coordinated by Marie Jackson of UTAH University (USA) carried out research published in the scientific journal American Mineralogist. They took numerous "cores " of concrete in a number of Roman ports and examined its components, which turned out to be quicklime, volcanic ash, and pieces of terracotta. The scientists found that seawater reacting with them gave rise to the formation of aluminous Tobermorite, a mineral that strengthened the concrete structure.
The Romans sourced volcanic ash from deposits located near Rome called pozzolane rosse and in the Gulf of Naples near Pozzuoli hence the name Pulvis Puteolanus. When they were far away they used finely ground terracotta powder. With cocciopesto the Romans waterproofed walls of aqueducts sewers , built bridges, thermal buildings, heated houses, mosaic finished floors that can still be admired today in Pompeii: a thickness of 10/15 cm. was placed over the foundations and beaten with wooden pestles so that the various fragments were well compacted. The floor thus became impermeable to water. While it is in Roman times that the earliest writings mentioning lime and pozzolan or lime and earthenware are found, however, in the island of Cyprus, constructions dating back to 2,000 B.C. have been found in which lime and ground fired clay had been used. By the 10th century, lime and pozzolan mortar was known to both the Phoenicians and the Israelites, who used it to plaster the inside of cisterns in Jerusalem. It was the Romans, however, who upgraded the use of this mortar, using pozzolanes (volcano ash and ground brick powder-cocciopesto) in place of sand. With this technique they built the most important monuments of antiquity, such as the Pantheon in Rome, which still endure millennia after their construction. The explanation is simple: in ancient times the components of lime mortar were not altered by foreign components that modern chemical knowledge has introduced, and therefore the characteristics of mortar were derived from the natural characteristics of its components. As for lime mortar, in addition to the choice of limestone, important was also the firing, which was done slowly with wood at a low temperature (between 800° and 900°). In fact, there were no gas kilns that modernly cook quickly and at high temperature with the risk of not obtaining perfect firing and consequently to the detriment of the quality of the final product. As for the terracotta powder, it was derived from the fragments of amphorae, tiles and bricks, the production of which was done with pure clay fired for a long time in a wood fire. Again as with lime, the 2 elements that contribute to the final result are a long wood-fired firing and the raw material: pure clay without the addition of industrial waste. Industrial sludge is to all intents and purposes waste and as such is regulated by Legislative Decree 152/2006. In Italy, industrial sludge is mostly disposed of in landfills, but it can also be disposed of and in fact is disposed of in asphalt, concrete and brick production cycles. It goes without saying that brick production waste containing industrial sludge, even in large quantities, does not have the hydraulic power of cocciopesto derived from pure clay, and restorers who have to skim the market offerings and look for those who still produce bricks and cocciopesto using ancient techniques know this well.
A testimony of how this need is felt is given, for example, by Dr. Federica Fenzi, who in a direct email to Antica Fornace Carraro wrote
"I teach chemistry at the Academy of Fine Arts in Verona (undergraduate restoration course). I am pursuing a dissertation on the in situ relocation of a late Roman mosaic. Reviewing the ground sherds in circulation, I was confronted with disaster: almost no sherds are hydraulic (for high corttira T) the remaining part is not, and moreover it has already been mixed with pozzolan and lime. I urgently need to find a reliable and continuous supply channel, for this and future restorations." If you are available in this regard and would like to contact me, I will leave you my number [...]. Thank you and have a good day, Federica Fenzi.
Graduated in chemistry in 2000 from the University of Padua, she carries out research activities at the National Research Council in Padua (from January 2001 to May 2014), conducting archaeometric studies on ancient materials with inorganic matrix, such as glass, ceramics, bronze, pigments, hydraulic binders and developing synthesis of eco-sustainable materials for industry and restoration of ancient materials. He is an adjunct professor for the a.y. 2011-2012 of the course "Chemistry for Cultural Heritage" for the degree program in Cultural Heritage at the University of Verona - Faculty of Humanities. Starting from a.y. 2013-2014, he is an adjunct professor of the course "Elements of Applied Chemistry for Restoration" at the Academy of Fine Arts of Verona, Five-Year Single-Cycle Diploma in Restoration. Siltea S.R.L. Spin Off of the University of Padua has carried out macroscopic and in digital microscopy, mineralogical petrographic and chemical analyses by X-ray Fluorescence comparative analyses between bricks made with ancient techniques at the "Antica Fornace Carraro" and original bricks from the Roman period. The analyses were conducted at the laboratories of the CNR (National Research Council) Institute of Geosciences and Resources U.O.S. in Padua, Italy. The results show a high correspondence between the two samples: the relative chemical compositions are fully comparable and similar to each other.
Making earthenware plaster is an ancient tradition established over thousands of years. Cocciopesto was widespread in all its uses in the Venice of the Doges. Cocciopesto continues to live on today thanks to those who believe in natural building known as biobuilding. Ground earthenware is a natural plumber for mortars. It has several colorings. red, yellow and burnt and different grain sizes from the ventilated Filler powder to coarse chunks
Foto n. 1
Queste sono le pezzature che vengono utilizzate per la maggior parte ma se c’è la necessità di grossi spessori o nel caso calcestruzzo o di pavimentazione vengono utilizzati grani con diametro maggiore
2a Misto paglierino e rosato da 4 a 5 (senza polvere)
2b Brucione paglierino da 0 a 4
2c Misto paglierino e brucione da 3 a 4
2d Brucione da 3 a 4
2e Misto paglierino e brucione da 4 a 5
2f Misto brucione da 4 a 5
Cocciopesto based on slaked lime and ground terracotta is a macroporous, breathable, elastic, deudimifying, antifreeze, waterproofing product resistant to environmental climatic aggressions in marine areas, does not produce salt efflorescence ( in fact, water passes through and evaporates, leaving the salts to pass outside where they can be brushed away, while where there is cement the salt accumulates in the plaster, creating swellings that then burst) , prevents condensation mold from forming ( blackish spots that bloom on the wall), is antibacterial ( lime has always been used as a disinfectant)
Use of cocciopesto
It should be noted that in the execution of the old walls the use of whole bricks was used mostly in valuable buildings, left facing but which were the minority. In all the others, in addition to whole bricks, pieces and flakes or bricks and stones together were also used and therefore it was necessary to use a good bedding mortar that held all the pieces together; generally these walls were covered with plaster which also had the function of reinforcing the walls, protecting them from rain, maintaining the internal temperature and finally also a decorative value in case it was enriched with friezes and paintings. Currently in the renovations of old buildings, as the aesthetic side of the old walls is appreciated, there is a certain tendency to remove the old plaster and leave the walls exposed. In this case it is advisable to be very careful not to weaken the walls themselves, the old joints must be grouted with care and with compatible mortars based on lime putty cocciopesto and sand
Photo no. 4 - Bricks and stones with bedding mortar based on lime putty, sand and yellow cocciopesto
Photo no. 5 - Stone wall with bedding mortar based on slaked lime sand and burnt cocciopesto which gives the mortar a gray color
If the wall is compact and in good condition, it can be left exposed, however taking care to fill the holes between the stone very well with lime putty, sand and burnt cocciopesto mortar which gives the gray colour.
If instead the masonry is mixed between ancient and modern or the wall is disconnected then it is advisable to plaster the wall.
Photo no. 8 - Example of the various passages: (A) spreading of the bottom in cocciopesto; (B) application of rough lean plaster; (C,D,E) different colors of the marmorino finish.
Next steps to run a sample: photos 9, 10, 11, 12, 13,14
First you wash the wall. Then, before applying the lime putty and cocciopesto-based plaster, the wall is wetted with lime water; this allows the small particles that make up the putty to penetrate the wall developing the adhesion of the plaster that lasts over time.
Photo no. 9 - We make the guides for the thickness of the plaster we want to make
Photo No. 10 - Pour the cocciopesto with the trowel
Photo n.11 - level with the straight edge
Photo n.12 (Application on the wall)
Depending on the thickness needed to straighten the wall, one or more layers of cocciopesto are laid.
As regards the granulometry of the cocciopesto, two factors must be kept in mind: the granulometry must be curved, i.e. the diameter of the grains must go from the largest to the finest, to cover all the spaces so that the plaster is compact, as regards the of the larger grains, the thickness of the plaster must be taken into account; the more irregular the walls are, the more coarse grain we will have to introduce into the dough. In deciding the thickness of the plaster it is also necessary to bear in mind that the greater the thickness, the greater the ability of the plaster to dispose of the humidity of the wall. To plaster an old and damp wall it is good to start from a minimum thickness of 4 cm. In addition to the various grits when cornering, it is important to use ventilated powder (which is like an impalpable powder) because it fills all the empty spaces. Add the water and mix well with the mixer.
Photo no. 13
If the cocciopesto serves only as a base then it will be a rough finish so that the next layer of plaster adheres better.
Photo no. 14 - If, on the other hand, you want to have a plaster in cocciopesto only, proceed with the final smoothing with a wooden trowel.
Photo no. 15 If you want to cover with a layer of white plaster, make a mixture with one part of lime putty and two parts of 0/2 grain size limestone powder
Up to this finishing stage we have maximum transpiration of the wall which absorbs and releases humidity, reducing the phenomena of mold and condensation.
Photo no. 16 - Marmorino plasters
If you want to finish with a marmorino, a mixture is made with one part of lime putty and one part of fine calcium carbonate. It is spread with a trowel and crushed with iron. As far as the final color is concerned, we have the three fine terracotta powders available: yellow and burnt pink which gives a gray color to the finish. If you want other colors you resort to the use of mineral pigments derived from natural colored soils called more simply colored earths that are found in special shops known to lovers of products for conservative restoration.
It is finished by spreading a cream on top with the iron obtained by passing the mixture through a veiling sieve which covers any imperfections. As long as the plaster is still fresh, if we want to obtain the waterproofing of the wall, the plaster must be passed over with flakes of Marseille soap hot dissolved in lime water and spread with rotary movements with a special stone. The soap in contact with the limestone forms limestone soap which is no longer water soluble, giving the marmorino its characteristic impermeability without however preventing the passage of steam from the inside to the outside of the wall. This process gives the plaster those white shadings characteristic of soap. This finish is used for the external plasters photo n. 17 and 18, in the kitchens (photo n. 19) and in the bathrooms also inside the shower (photo n. 20) .
To obtain adequate results, the realization must be entrusted to expert craftsmen.
Examples of creations in cocciopesto
Photo no. 17
Photo no. 19
Photo no. 20
Photo no. 21
A particular decoration of marmorino is the marble effect
Photo no. 22
Photo no. 23
Photo no. 24
Photo no. 25
Finally, various decorations can be performed above the marmorino
The rooms finished in marmorino with decorations denote an extraordinary elegance
Photo no. 26a, 26b
Frames, relief decorations, frescoes can be made
Interiors of bathrooms and saunas made in lime putty, cocciopesto and hemp by the well-known Piedmontese craftsman Danilo Dianti.
Photo no. 28, 29
Sound-absorbing internal walls
In modern buildings, for reasons of weight and speed of execution, the internal partition walls are often made with plasterboard. However, this entails the inconvenience of the transmission of noise from one room to another.
If you want to remedy this problem, you have to go back to the old system of making the internal walls with a warping of wooden beams filled with a mixture of lime putty, earthenware and straw well compacted inside the wooden frame which you proceed to cover with arelle, close to the arelle a rough coat of cocciopesto must be carried out followed by a layer of rough plaster and a smooth cocciopesto finish. This type of wall, if skilfully executed by expert craftsmen, guarantees excellent thermal and acoustic insulation and is water regulating (if there is more than 50% humidity in the room it absorbs it, if it is less than 50% it releases it) .
Photo no. 30 - Heated walls
Heating pipes can pass inside these walls. This system can be particularly appreciated for the walls of the bathrooms where, in addition to guaranteeing the breathability of the wall, the drying of clothes hung on the hooks fixed in the wall can be speeded up.
ACOUSTIC INSULATION BETWEEN FLOORS
Photo no. 31 - Sound-absorbing floor
Noises are divided into high-frequency noises (conversations coming from the neighboring room, loud radio and television conditioning systems) and low-frequency noises (trampling). Each noise can be reduced by the appropriate material and its correct application.
To obtain excellent acoustic (as well as thermal) insulation of the attic, the best materials to use are porous sound-absorbing ones and since cocciopesto is known to be a macroporous material, a bunch of slaked cocciopesto placed on top of a layer of straw combines sound absorption with lightness of the weight. It must be built with the MASS-SPRING-MASS system, i.e. between the actual attic and the floor. Let's give an example of how a correct restoration of an attic in a historic building should be carried out: the 5cm multilayer wooden panels must be placed over the original wooden beams and planks, they must be hooked to the perimeter walls with steel pins for the purpose to make the floor load-bearing; sheets of oiled paper are placed on top, a pair of 12 cm high wooden morals is placed on top. at a distance of 80cm, these morals act only as guides and must be moved as the dough is spread; a large tub is filled with lime milk and the chopped straw is soaked. The lime kills all bacteria and insect larvae that may be present in the straw, drain the straw and spread it between the morals, compressing it well with the help of a jute sheet spread over it, fix it to the underlying planks by means of long steel screws with a framework of steel wires, the morals are moved until the whole room is covered with a 12 cm layer of straw and lime. At this point, a 10 cm bunch of lime putty and cocciopesto is spread over it. Above which the floor should be laid (possibly handmade terracotta tiles).
Photo no. 32 - If you decide to lay solid wood as flooring, then inside the bunch of cocciopesto you need to drown some wooden bagatelli (moraletti) on which you will then anchor the wooden planks.
Photo no. 33 - Pipes for underfloor heating can also be placed under this screed.
3. TERRAZZO ALLA VENEZIANA
As far back as antiquity, the mixture of lime putty and earthenware was used for flooring often decorated on the surface with mosaics arranged to form splendid designs. Examples have been found in republican houses and in the villas of Pompeii, but it was at the time of the Most Serene Republic of Venice that this floor had its greatest splendor. The thickness was substantial, both to counteract moisture and for reasons of elasticity: in fact, the higher the thickness, the further away the risk of surface cracks. It is composed of two layers. A base layer that is thinner (i.e., with less lime) and coarser and a second layer that is fatter and with the grits chosen according to the coloration and size you want to see on the surface when the floor is finished. The grits should be curved i.e., the size should range from the largest to the smallest and also contain very fine powders so as to fill all spaces. First you have to calculate the total amount of grits needed according to the surface to be paved (about 20 kilograms of grits pe a square meter one cm high), dose the various components according to the chosen recipe (pour the total amount of grits in a square and mix it dry carefully, do the same with the ventilated cocciopesto and calcium carbonate powders. This will allow for a uniform-looking floor and not patchy as would happen if you dosed each individual dose that goes into the concrete mixer because no matter how much care is taken there would still be differences, albeit small ones, that would affect the final result. Pour into the cement mixer first the powders and mix them then add the grits previously soaked with milk of lime and mix everything lastly add the slaked and mix well. With the wheelbarrow spread the mixture on the slab, pull it with the tongs make the desired surface seeding with coarser terracotta or marble chips and slowly beat it and smooth it with a trowel until the water comes to the surface and you can no longer see the stones popping up but the floor looks smooth; keep the floor covered with a nylon sheet until the next day to slow the drying, the next morning beat it well and then cover it and so on until slowmenta dries at which point flood it with raw linseed oil until saturated then sand it with water then when it is dry to close all the holes make a paste with tailor's plaster and cooked linseed oil and sand it again, so on until all the holes are closed. Finally give a coat of boiled linseed oil and wax.
This is a poorer Venetian terrazzo without surface seeding but with only very fine impasto and colored with cinnabar to appear red; it was common in Venice in the 16th century.
Photo no. 35 - Cocciopesto floors with terracotta inserts.
Cocciopesto reconstruction original Nanto stone arch.
Cocciopesto can be used to reconstruct stone window surrounds that have deteriorated over time. As can be seen in the photograph, the right side of the photo shows the reconstruction in earthenware of the pillar placed around the window; on the right we see the partial covering of the earthenware with white lime putty and carbonate plaster, and to the side the finishing with a lime putty-based plaster and ground Nanto stone powder.
Photo No. 37 - Consolidation of old floors with lime putty and earthenware
Lime putty and earthenware patching of old ceilings with arelle
Execution of the roof of his own house personally done by bioartisan Manuel Foralosso
The roof that was insulated with straw drowned in lime milk and covered with lime putty screed and earthenware.
- below go the rafters
- above planks
- above, morals
- between each moral, thatch is placed
- above the thatch, wooden boards placed crosswise
- above, tile roofing
In this way, a ventilated roof is obtained
Photo No. 40 - Foundations made personally by bioartisan Manuel Foralosso
Example of the foundation of a green building house, made with burnt bricks laid with lime putty mortar and cocciopesto powder with excellent mechanical and hydraulic resistance. Brucioni bricks are almost vitrified, so they do not absorb water and have excellent mechanical strengths.
Photos 41, 42, 43 - Restoration of old floors with grout made from earthenware, lime putty and colored earth.
Ventilated earthenware can also be used in water purification filters and as an agricultural fertilizer.
As we have been able to see, in both ancient and modern times the use of lime putty with earthenware gives excellent results in all fields of restoration and even green building.
However, it requires skilled workers who are passionate about their craft and a user base that is equally passionate and necessarily willing to spend a little more for the cost not so much of the materials as of labor. In recent years it has been noticed that many passionate people have approached this field and have successfully gone the DIY route to make up for the cost that an experienced craftsman's labor necessarily entails.
To meet this need, numerous courses have been established to teach ancient techniques. Prominent among them is the European Center for Heritage Trades - Villa Fabris Association (VI). However, for those who cannot afford the higher costs due to the use of more specialized artisan labor and the longer manual application time of these products, nor can they provide the work themselves, knowledge of ancient raw materials combined with materials technology have come to the rescue.
As mentioned above, Dr. Fenzi has not only conducted research at the CNR in Padua, but also carried out archaeometric studies on ancient materials, and developed syntheses of environmentally sustainable materials for industry and for the restoration of ancient materials. Based on this experience in multiple fields, he developed an innovative product based on hydraulic lime, micronized earthenware and natural microorganisms that combined the characteristics of lime and earthenware with the ease of installation using modern techniques.
It is precisely at this point that innovative know-how comes into play, thanks to which cocciopesto is able to actively defend itself in adverse environments. More precisely, the cocciopesto is additivated with a liquid product based on beneficial microorganisms (non-GMO) and a powder additive that forms the heart of the innovation. Preliminary data and site application tests indicate that the best results are obtained in saturated salt solutions (chlorides and sulfates), in which the additivated cocciopesto observes a progressive improvement in mechanical properties, where their drastic decrease would be expected.
44 - Example of a wall affected by moisture surfacing, caused by normal cement mortar
45 - the same wall restored after the cementitious mortar was removed and a mortar based on natural hydraulic lime, micronized cocciopesto with powdered additive based on beneficial non-GMO microorganisms was given back
In conclusion, it can be said that the alliance of lime and earthenware in its various combinations and possibilities is undoubtedly a winner, which is why architects who are passionate about their craft have rediscovered it.
Mastering the ancient techniques and knowing how to provide proper installation of these materials, guarantees the craftsmen who approach this world a steady, well-paid and satisfying job. End-users who do not delegate to others but take a personal interest, study, study in depth and make an informed choice in the use of these products, instead of the generic industrial ones found on the market, obtain an end result of livability of their home that will satisfy them not only in the immediate but with continuity over time.