What is Plaster?
Noun 1. A mixture of lime, sand, and water that is applied to a wall or ceiling as a soft paste and dries as a hard coating 2. An adhesive strip of material for dressing an injury, such as a cast |  |
Verb 1. To coat (a wall or ceiling) with plaster 2. To apply like plaster: he plastered his face with shaving cream 3. To cause to lie flat or to adhere: his hair was plastered to his forehead [Greek emplastron healing dressing] |
Plaster was used by the Egyptians (chiefly as a surface to receive color decorations) and by the Greeks. The Romans used it extensively, and there remain, especially at Pompeii, many ceilings and walls, with beautiful relief ornamentation, of a hard, fine plaster. Italian Renaissance artists imitated this Roman work, and relief ornament in plaster was employed in England for the rich ceilings and interiors of the reigns of Henry VIII, Elizabeth I, and James I and later in those designed by the architects Robert and James Adam. In the United States many fine ornamented plaster ceilings were executed in the 18th century. |
Interior plastering is applied over a base that will furnish a proper grip—by means of interstices provided by wood lath or metal lath or by irregularities of surface such as in hollow tile. To secure best results three successive coats of plaster are requisite in most types of work. 1. The first, or scratch, coat composed of sand and lime mixed with abundant hair or fiber, must be thoroughly grounded into the lath and before it hardens is scratched to provide key, or adhesion, for the next coat. 2. The second, called the brown coat in the United States and the floating coat in Great Britain, is composed of sand and lime, without hair, and is worked to a hard, compact texture, with its surface roughened to receive the final coat. 3. The third or white, finishing coat is composed of plaster of paris, slaked lime, and white sand, mixed with water to form a paste. It is troweled on the wall to form a hard, smooth surface, the process requiring a skilled worker. |
Moldings, cornices, and relief ornament are cast separately and then mounted into place. In former times ornamental details were molded in their location, from the damp plaster. Often substituted for plastered walls is plasterboard, a prefabricated material composed of paperboard and gypsum. |  |
Bibliography:
Collins Essential English Dictionary 2nd Edition 2006 © HarperCollins Publishers 2004, 2006 The Columbia Encyclopedia, Sixth Edition F. Van Den Branden and M. Knowles, Plastering Skill and Practice (1953, repr. 1971) J. R. Diehl, Manual of Lathing and Plastering (1960, repr. 1965)
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