plaster arch

plaster

Usually a mixture of gypsum or lime with sand and water, producing a paste-like material that is applied in the plastic state, usually over lath fastened to a surface such as a wall or ceiling, or sometimes directly onto brick; it forms a hard surface when the water it contains evaporates. In some remote early settlements, when lime or gypsum was not available, a so-called plaster of fine white clay mixed with chopped straw was sometimes troweled onto a surface to produce a smooth finish on a wall or ceiling. Cow hair, cow dung, and/or chopped straw often was added to the plaster mixture to increase its mechanical strength when it dried. Gypsum later supplanted lime as the plaster of choice because of its superior properties. Also See mud plaster, ornamental plaster, plaster of paris, and stucco.