Plaster has been around for centuries and the desire for smooth monolithic walls is still the preferred look. We know that 5,000 years ago the Egyptians burnt gypsum and then crushed it into a powder then mixed it with water to be used as a joining compound for the massive blocks to build the pyramids.
Traditionally in the US, gypsum plaster was applied in three coats. The first coat was called the “scratch coat” which was applied over wood lath or metal lath and put on at a thickness of 1/4″ – 1/2″ in one pass, then scratched with a scarfier or some type of rake to help “key in” the next coat. The second coat or “brown coat” was applied the next day or within a few days and long straight edges or “darbies” were used to flatten the wall. This coat was finished smoother but left a little rough to allow the final coat to bond.
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This second pass was also applied at a similar thickness as the first coat. The third and final coat was the “finish coat”. This last coat of plaster was a much thinner application and usually hard troweled to a smooth finish. The finish coat was usually painted but before paint was available, the product was integrally colored or left the natural color of the raw materials. This look is what most will call “Venetian Plaster”, “Faux Plaster” or “Polished Plaster”.
Most people today will call any smooth finished wall with color variation “Venetian Plaster”. Venetian plaster is more of a style or technique of multiple thin coats layered one on top of the other to create the appearance of depth. Most plaster today is applied directly over prepared drywall and is done in much thinner coats. The thickness of the plaster system will depend on the preparation of the drywall substrate. Very thin plaster systems will require the drywall to be finished to a level 4 or 5, or will require a thicker plaster base coat to cover and smooth out the imperfections in the drywall. Thicker plaster systems may not require any taping of board joints and inside or outside corners, but will require some sort of treatment before applying a finish coat.
Today there are many different plaster materials to choose from including gypsum, cement, lime, acrylic and even clay. Lately the most popular are acrylic plasters which can be purchased at most any box store, online or at a specialty supply house. It is important to find the correct product for the particular application. Acrylic plaster is easy to apply, can be patched, is incredibly durable and the installed price is usually less expensive. The most popular reason to hand trowel plaster is that it is integrally colored and the color is varied to give depth in the wall or ceiling, so color options should be a high priority when choosing an interior plaster. Typically, interior acrylic plaster may be tinted to any color imaginable for a very low cost compared to clay plaster, gypsum plaster, lime plaster or cement plaster. The reason is that the product is much thinner and the colorants are readily available and inexpensive. Since most all acrylic plaster is manufactured domestically and the coverage is superior to most other plasters, it is an economic choice for a plaster system.
Author: Timothy Williams, Owner, Volterra Architectural Products
Volterra Architectural Products manufactures distinctive architectural elements for interior and exterior use including faux wood beams, corbels, brackets, shutters and truss tails. Interior/exterior finishes include limestone plaster, gypsum plaster, acrylic plaster and exterior stucco (including EIFS). Volterra also produces decorative cast resin products for the tile and stone industry, as well as manufactured stone veneer.