Plaster coats walls and ceilings. Plaster is a building material. Plaster starts as a dry powder and is mixed with water to form a paste which liberates heat and then hardens. Plaster can be easily manipulated with metal tools or even sandpaper. Plaster is often used as an artistic material for casting. Plaster is used in arts, in medicines as a support for broken bones, in fire protection as fireproofing product. Plaster is used in dentistry for mounting casts or models of oral tissues. Plaster is also used in architecture to create complex detailing in room interiors.