What's lime got to do with it?

The purpose of this post is to create a glossary to clear up confusion with some of the buzz words we hear around plaster and lime.

LIMESTONE: is sedimentary rock made up of the mineral calcite in its crystallized form known as calcium carbonate (CACO3). Its found all over the world, not just in Italy.

MARBLE: some limestone has gone through a metamorphosis (recrystallization) and became marble. Pure marble is only made of CACO3 and is white. The beautiful colors that are found in marble are from other minerals (i.e. iron oxide, clay) that were on the limestone when it metamorphosed into marble.

LIME PLASTER: is made through a process of cooking chunks of limestone until it disintegrates into a powder which is called calcium oxide. When water is mixed with calcium oxide it becomes calcium hydroxide also known as slacked lime. Slacked lime can come in powder form or when more water is added it becomes a paste. The paste form is what we call lime plaster.

PLASTER: In general, plaster can be made of gypsum, portalnd cement, lime or combinations there of. Plaster is also called stucco with usually has cement in it.

100% Lime Plaster: Means it is only made up of CACO3. Since marble is also CACO3, marble dust of various size can be mixed in with the paste and still be considered a 100% lime plaster. Lime plaster has been used for 1000's of years all over the world as an exterior or interior finish. When lime plaster is drying on a wall its called carbonating. During this process CO2 is being drawn into the plaster to help turn it back onto stone.

VENETIAN PLASTER: Is a misnomer in the United States causing much confusion for home owners, builders, architects and designers. We see this everyday at Italian Plasterworks. Back in the day, when the grand villas were being built along the canals in Venice, it was popular to use large marble slabs as your wall finish. The villas could not support the weight of the slabs so craftsmen created very fine plasters to emulate the look of a marble slab. The craft of marbleizing was born. Venetian plaster can be more considered a technique but still people haves different ideas as to what that outcome should look like.

ITALIAN PLASTER: Italians have been making lime plasters for hundreds of years. Plasters are used as much as paint in Italy. Due to delicate restoration work done in Italy, Italians have purity laws regarding the ingredients of their plasters thus are considered to make the best plasters in the world. Safra, Firenze and Firmolux are a few of the companies that export their plasters to the US. In the US, you and I could throw paint, lime, and gypsum in a bucket and market it as Venetian Plaster. Some North American companies are entering the market with high quality lime plasters such as Totem Coatings and Vasari.

VENEZIANO: is a term associated with a high polished plaster. Venezianos are made by most plaster malefactors and are very popular. Most Venezianos are not 100% lime as 100% lime plasters are hard to apply with little or no training. So most Venezianos are acrylic based to meet the needs of the contractors. Veneziano Photo

MARMORINO: Means little marble in Italian. Typically, a marmorino plaster does not have the high gloss sheen of a Veneziano but more of a semi-gloss appearance. Marmorino Photo

Benefits of 100% lime plaster: Lime plaster has been "green" since its conception because its just limestone. Even the process of making plaster from limestone is green. Because lime is caustic it resists mold, mildew and bacterias from growing on its surface. Its flexible enough that it doesn't have the cracking problems that plasters and stucco created with cement have. It draws CO2 form the air when its drying and is breathable. Some plasters are labeled "lime based". This can be anywhere from 10% to 99%. A plaster with only 10% is not going to have the same benefits as a 100% plaster.

Drawback of 100% Lime Plaster: The skill of correctly applying lime plaster takes training and practice. Both the California School of Italian Plasters and the Midwest School of Italian Plasters offer a week long program.

FAUX FINISH: Faux just means fake in French. Before fine finish plasters were readily available, artists used paints and glazes to emulate the look of a real plaster. So a wall with a plaster finish isn't a faux finish, its a real finish. But to confuse things, artists use real plasters in such a way to create an old world look which would be a faux old wall.