Into this circle he pours water, and then sprinkles the water with plaster.First the plasterer creates a “gauge” that is a circle of putty, banked up like a swimming pool, on the mixing board.This lime putty is used for the finish coat of plaster that is skimmed onto the wall and smoothed to create a hard, shiny finish coat. “This is where art meets science,” Bob says, as he watches the mix being prepared for the lime putty. With a traditional lime finish coat, the plasterer becomes a chemist.

Finish coat: The third and final coat is an application of lime putty, which gives plaster walls their smooth, hard, shiny finish.

The sand provides a rough texture that gives the light, 1/8-inch finish coat a surface to grip onto. Brown coat: The second rough coat is made of the same mixture and is called the “brown coat.” The brown coat is applied directly to the scratch coat, also at a 3/8-inch thickness, but left unscored.Scratch coat: The first coat is called the “scratch coat” and is applied at 3/8 inch thick then scratched or scored with a comb to give it a rough texture.Boro Plastering works with a ratio of three-to-one, bags of sand to bags of gypsum, for their rough coats. Many firms now work with gypsum since it eliminates the need for added fiber and has a much quicker set up and drying time. The lime is typically derived from limestone or ground oyster shells. These coats form the base of the wall and are mixed of lime or gypsum, aggregate, fiber, and water. The three-coat plaster system begins with two coarse or rough coats.

Plaster and lathe walls