Stucco

Stucco or render (Persian: گچ بری Gachbori) is a material made of aggregates, a binder, and water. Stucco is applied wet and hardens to a very dense solid. It is used as decorative coating for walls and ceilings and as a sculptural and artistic material in architecture. Stucco may be used to cover less visually appealing construction materials such as metal, concrete, cinder block, or clay brick and adobe.

In English, stucco usually means a coating for the outside of a building, and plaster one for interiors; as described below, the material itself is often little different. But other European languages, importantly including Italian, do not have the same distinction; stucco means plaster in Italian and serves for both. This has led to English often using "stucco" for interior decorative plasterwork in relief, especially in art history and older sources.

Composition

The difference in nomenclature between stucco, plaster, and mortar is based more on use than composition. Until the latter part of the nineteenth century, it was common that plaster, which was used inside a building, and stucco, which was used outside, would consist of the same primary materials: lime and sand (which are also used in mortar). Animal or plant fibers were often added for additional strength. In the latter nineteenth century, Portland cement was added with increasing frequency in an attempt to improve the durability of stucco. At the same time, traditional lime plasters were being replaced by gypsum plaster.