Plaster is a building material used for the
protective or decorative coating of walls and ceilings and for molding and
casting decorative elements. In English "plaster" usually means
a material used for the interiors of buildings, while "render"
commonly refers to external applications. Another imprecise term used for
the material is stucco, which is also often used for plasterwork that
is worked in some way to produce relief decoration,
rather than flat surfaces.
The most common types of plaster mainly contain
either gypsum, lime,
or cement, but all work in a similar way. The
plaster is manufactured as a dry powder and is mixed with water to form a stiff
but workable paste immediately before it is applied to the surface. The
reaction with water liberates heat through crystallization and
the hydrated plaster then hardens.