The History of Marmorino
Marmorino is well known as a classic venetian plaster; however, its origins are much older, dating to ancient Roman times. We can see evidence of it today in the villas of Pompei and in various Roman structures. In addition, it was also written about in Vitruvio's "De Architectura", a 1st Century B.C. history of Rome. Marmorino was rediscovered centuries later after the discovery of Vitruvio's ancient treatise in the 15th century. This 'new' plaster conformed well to the aesthetic requirements dictated by the classical ideal that in the 15th century had recently become fashionable in the Venetian lagoon area.
The first record of work being done with marmorino is a building contract with the nuns of Santa Chiara of Murano in 1473. In this document, it is written that before the marmorino could be applied, the wall had to be prepared with a mortar made of lime and "coccio pesto" (ground terra cotta). This "coccio pesto" was then excavated from tailings of bricks or recycled from old roof tiles.
At this point, to better understand the popularity of marmorino in Venetian life two facts need to be considered. The first is that in a city that extends over water, the transport of sand for making plaster and the disposal of tailings was, and still is, a huge problem. So, the use of marmorino was successful not only because the substrate was prepared using terra cotta scraps, but also the finish, marmorino, was made with leftover stone and marble, which were in great abundance at that time. These ground discards were mixed with lime to create marmorino.
Besides, marmorino and substrates made of "coccio pesto" resisted the ambient dampness of the lagoon better than almost any other plaster. The first because it is extremely breathable by virtue of the kind of lime used (the only lime which sets on exposure to air after losing excess water) and the second, because it contains terra cotta which when added to lime makes the mixture hydraulic, that is, it's effective even in very damp conditions (because it contains silica and aluminium, bases of modern cement and hydraulic lime preparations). The second consideration is that an aesthetically pleasing result could be achieved in an era dominated by the return of a classical Greco-Roman style allowing less weight to be transmitted to the foundation when compared to the habit of covering facades with slabs of stone.
Usually, marmorino was white to imitate the stone of Istria, which was most often used in Venetian construction, but was occasionally decorated with frescoes to imitate the marble, which Venetian merchants brought home from their voyages to the Orient. (In this fascinating period of the Republic of Venice, merchants felt obliged to return home bearing precious, exotic marble as a tribute to the beauty of their own city.)
Marmorino maintained its prestige for centuries until the end of the 1800's when interest in it faded and was considered only an economical solution to the use of marble. Only at the end of the 1970's, thanks in part to the architect, Carlo Scarpa's use of marmorino, did this finishing technique return to the interest of the best modern architects.
For about 10 years, industries were also interested in marmorino which was only by produced by artisans. Today, however, ready-to-use marmorino can be found, often with glue added to allow them to be applied on non-traditional surfaces such as drywall or wood panelling.
Venetian Marmorino Stuccos
VENETIAN STUCCO – The Material
In Venetian culture, Venetian Stucco has always been considered the most refined and decorative. The original recipe for Venetian Stucco contained: powdered lime, glue made of animal by-products, and color pigments. The plaster used, which is no longer reactive and has lost its capacity to set is considered inert. Its PH is near 7 and is therefore considered neutral.
The glue that was used in the past was subject to deterioration and, therefore, had to be used soon after it was made. Today, an industrial acrylic glue is typically substituted, or in any case, a glue which is not subject to mildew and which can mix well with the powered lime. The amount of glue used in the stucco is the minimum necessary to guarantee optimal bonding and long-lasting durability.
Most colors of the spectrum can be achieved with the color pigments available today. OR The color pigments available today can be mixed to achieve most colors of the spectrum. These are resistant to UV deterioration because of its neutral medium. (A PH of more than 7 increases the likelihood of damage by UV rays) Besides the 3 basic ingredients, other materials are sometimes added, such as wax or oil, which makes the mixture more fluid and workable, or methylcellulose to make it lighter.
VENETIAN STUCCO – Its application
This plaster is for interior surfaces. Knowing the basic characteristics of Venetian Stucco will help you to understand which substrate is ideal for it. It is quite a rigid plaster, which, however, bonds very well to the substrate of the wall. It is, therefore, necessary to exclude all surfaces which are flexible or in any case, can expand and contract such as natural woods or PVC panels.
The ideal substrates are those of plaster, cement, and drywall even if they have been painted (though very old paint should be removed). Wood panelling also works well if it is not affected by humidity (chipboard, MDF panels, OSB, or marine plywood). The seams between the panels must be smooth (as is normally achieved with drywall. The wall's surface should be quite smooth. A wall finished with gypsum plaster is best.
First, several layers of plaster (usually 3) are applied and then the surface is sanded with diminishing grades of sandpaper. (The first coats can be plain or colored.) In the second phase, the final coats of colored plaster are applied with a thickness of a few tenths of a millimeter using a small spatula whose blade is 6 to 8 cm. in width. In this way, small strokes of color are superimposed one over the other during the application of the next 3 layers achieving hundreds of variations in overlaid color per square meter.
This part of the job requires considerable physical strength since each stroke of the spatula must have sufficient pressure to obtain a minimal thickness. It is also necessary for the artisan to be very experienced as well as precise when applying the final coats in order to obtain a uniform design with pleasing results. Gradually, as the plaster is worked with the spatula in this way always with considerable force and pressure, the plaster dries and becomes polished.
VENETAN STUCCO - Its maintenance
The surface is very smooth and therefore it is not subject to getting dirty. In Venice, it is easy to find perfectly preserved examples of this antique stucco which is more than 100 years old. However, Venetian Stucco is porous and permeable, and so is subject to absorb ambient moisture and the pollution which accompanies it. To avoid this, especially if the work has been done outside, it is possible to protect it with wax. Usually a natural wax, such as beeswax is used which not only protects, but also reduces its capacity to absorb allowing it to be cleaned more easily. This surface can be cleaned of all kinds of dirt and grime with plain water. Otherwise, it can be cleaned by a professional using special detergents .
It's advisable every few years to repeat the application of wax on the surface to guarantee continuous protection over time. This plaster is susceptible to water that can ruin its surface, so it must be protected from rain and other sources of water.
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Marmorino is a plaster composed of approximately 50% lime and 50% ground marble. Color pigments are added to achieve the desired color. The hydrated lime, comes from very pure limestone (CaCO3) and is baked to 900-950 C (1650-1740 F) and is conserved in water [Ca(OH)2]. It is alkaline and very white and sets up and hardens when in contact with ambient carbon dioxide losing only excess water.
The marble grains can vary in size depending on the desired effect, the largest granule not exceeding 0.8mm with the finest granules similar to flour. It's important that in each mixture there is a percentage of different-sized granules, from the finest to the largest. Color pigments can be added to this mixture whose base color is determined by the particular marble used. The colors are resistant to UV rays and can resist to PH over 7.
Once the mixture has set up, a very hard and compact surface is obtained. One reason for this is that marble and lime bind together homogeneously because they are chemically related (both CaCO3). In addition, the setting up process occurs only on the exterior surface which is in contact with atmospheric CO2, so only the exterior surface becomes extremely hard. Given the nature of this material, it can be preserved indefinitely inside a hermetically sealed container when kept from freezing. In the more modern mixtures glue is added (usually acrylic) to allow it to be applied to surfaces different from the more classic surface, which is made of a plaster mix of lime and sand.
MARMORINO -The Application
It is applied in 4 or 5 layers with steel trowels. The first layers are roughly applied and the last two layers are applied with increasing pressure so that the material is compressed to obtain a smooth finish. Normally, the first layer is applied and left to dry, while successive layers are applied wet on top of wet. The final result depends on both the way the layers are applied and the size of the marbles granules used. The thickness of each layer corresponds more or less to that of the granules used. There are various techniques used to obtain the highest lustre, but the common practice is for the last layer to contain the finest powdered marble. The ideal substrates are those of lime or gypsum plaster, cement, or drywall even if the surfaces have already been painted and the paint is not peeling (in this case the paint must beremoved). Marmorino can also be applied on chipboard, medium density, and OSB, but the seams must be joined in a way to insure a continuous, smooth surface (as is typical with drywall seams).
In addition, the surface should be smooth, or at most moderately rough. In the latter case, the different levels of plaster must be taken into consideration since they may be visible in the final design. The total thickness of the plaster will vary from 1.4 mm. to 2.5 mm. For each square meter, it will take form 1.7 to 3 kg. of marmorino (plaster).
MARMORINO – Maintenance
It is not difficult to maintain marmorino. First because the surface is very smooth, it doesn't get dirty easily. Besides that, it becomes harder with time, until it becomes rock hard. It is, however, a porous material and it is best to protect it with wax, usually beeswax, to be applied in high risk areas like kitchens and public areas, or anywhere where it could become watermarked into contact with splashes of liquids which could discolor it (like wine, coffee or oil).
It is very resistant to water. In fact, it can be used inside shower stalls and is considered as well a great exterior finish as can been seen on the many facades in Venice. If after several years it is necessary to clean it, it can be done so. If it has been waxed it is sufficient to use normal detergent or even plain water. Otherwise, it is best to have it cleaned by those who specialize in cleaning polished stucco.
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