Sand Sand makes plaster porous and thus facilitates the transformation of caustic lime into carbonate of lime. The texture of sand is important. Coarser sand is best for the undercoat and fine sand for the upper coats of plaster (there will be specific grain sizes suggested later.) All the sand should be of a uniform grit and the grains should be angular in shape. They should feel sharp and not roll like a ball between the finger. The idea is to squeeze the mortar tight. An artist must be particular about the type of sand mixed into the lime plaster. And once the proper sand is chosen, the sand must be washed and stored off the ground. Sand must be free of loam, clay, mica, and gypsum. Humus and loam in sand are dangerous because they decompose when exposed to air and cause efflorescence. Clay mixed in with the sand causes cracks in mortar. Water soaked sand containing clay weeps, exudes moisture, and makes it difficult for colors to adhere. Sand containing mica flakes will eventually split off from the
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