Plaster

Plaster is a building material used for coating walls and ceilings. It consists of a binder mixed with aggregate and water. The binder may be lime, gypsum, or Portland cement, and the choice affects strength, durability, and breathability.

Lime plaster is made from lime putty and sand. It can be hydraulic or non-hydraulic and cures slowly, developing flexibility and moisture permeability. Lime plaster has historic use in traditional architecture and in restoration work where humidity control is important.

Gypsum plaster, known as plaster of Paris, sets quickly and produces a smooth finish. It is commonly used for interior walls and decorative moldings, often applied in thin coats over a backing such as lath, board, or plaster base.

Cement plaster uses Portland cement with lime or sand as an aggregate and sets rapidly. It is strong and relatively water resistant, making it suitable for exterior applications (often as stucco) as well as rapid interior work.

Application methods include traditional lath-and-plaster systems, where multiple coats (scratch, brown, and finish) are applied over wooden or metal laths. Modern practice frequently employs plasterboard (drywall) or other drylining methods, with decorative plasterwork such as cornices and reliefs still produced in some settings.

External stucco refers to cementitious plaster applied to masonry surfaces, finished in various textures. Plaster is also used in non-construction contexts, such as plaster casts for medical immobilization, notably plaster of Paris.

Health and safety considerations include dust and skin irritation. Wet cementitious plasters can be caustic and require appropriate protection and ventilation during mixing and application.