plaster(redirected from impression plaster)
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a medicinal form in which substances are supplied for external application. Plasters melt or soften at body temperature and consist of such pliable substances as wax, paraffin, rosin, and rubber; sometimes medicines are added. Some plasters are used to protect the skin from external irritants or to hold bandages in place. Others have a specific therapeutic purpose; for example, keratolytic plasters are used to treat corns, lead plasters are used to treat furuncles and carbuncles, bactericidal plasters are used for purulent wounds, and pepper plasters are used in the treatment of such conditions as radiculitis and neuralgia. Plasters also include various adhesives that evaporate to form an elastic film on the skin, for example, collodion, Kleol, and the glue BF-6.
A plastic mixture of solids and water which sets to a hard, coherent solid and which is used to line the interiors of buildings. A similar material of different composition, used to line the exteriors of buildings, is known as stucco. The term plaster is also used in the industry to designate plaster of paris.
Plaster is usually applied in one or more base (rough or scratch) coats up to ¾ in. (1.9 cm) thick, and also in a smooth, white, finish coat about &frac116; in. (0.16 cm) thick. The solids in the base coats are hydrated (or slaked) lime, sand, fiber or hair (for bonding), and portland cement (the last may be omitted in some plasters). The finish coat consists of hydrated lime and gypsum plaster (in addition to the water). See Mortar