Stucco

Stucco or render is a construction material made of aggregates, a binder, and water. Stucco is applied wet and hardens to a very dense solid. It is most commonly used as a decorative and protective cladding for exterior walls and canopies. Stucco can be applied over construction materials such as metal, expanded metal lath, concrete, cinder block, or clay brick and adobe for decorative, protective and/or structural purposes. In English, "stucco" refers to a cladding for the outside of a building and "plaster" to a cladding for interiors. Other European languages, notably Italian, do not have the same distinction: In Italian, stucco means plaster, and serves for both.

Composition

The basic composition of stucco is lime, water, and sand. 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 mortar as well as plaster, which was used inside a building, and stucco, which was used outside, would consist of the same primary materials: lime and sand. Animal or plant fibers were often added for additional strength. Sometimes additives such as acrylics and glass fibers are added to improve the structural properties of the stucco. This is usually done with what is considered a one-coat stucco system, as opposed to the traditional three-coat method. In the latter nineteenth century, Portland cement was added with increasing frequency to cover surfaces in contact with soil or water. At the same time, traditional lime plasters were often being replaced by gypsum plaster. Lime is almost as good in balancing humidity as clay. It prevents moisture accumulation inside the building as well as in the wall by its excellent permeability, and is more elastic and workable than cement render. Lime itself is usually white; color comes from the aggregate or any added pigments. Lime stucco has the property of being self healing to a limited degree because of the slight water solubility of lime (which in solution can be deposited in cracks, where it solidifies). Portland cement stucco is very hard and brittle and can easily crack and separate from the surface if the base on which it is applied is not stable. Typically, its color was gray, from the innate color of most Portland cement, but white Portland cement is also available. Today's stucco manufacturers offer a very wide range of colors that can be mixed integrally in the finish coat. Other materials such as stone and glass chips are sometimes "dashed" onto the finish coat before drying, with the finished product commonly known as "rock dash", "pebble dash", or also as roughcast if the stones are incorporated directly into the stucco, used mainly from the early 20th through the early 21st centuries.

Traditional stucco As a building material, stucco is a durable, attractive, and weather-resistant wall covering. It was traditionally used as both an interior and exterior finish applied in one or two thin layers directly over a solid masonry, brick, or stone surface. The finish coat usually contained an integral color and was typically textured for appearance. Then with the introduction and development of heavy timber and light wood-framed construction methods, stucco was adapted for this new use by adding a reinforcement lattice, or lath, attached to and spanning between the structural supports and by increasing the thickness and number of layers of the total system. The lath added support for the wet plaster and tensile strength to the brittle, cured stucco; while the increased thickness and number of layers helped control cracking. The traditional application of stucco and lath occurs in three coats—the scratch coat, the brown coat and the finish coat. The two base coats of plaster are either hand-applied or machine sprayed. The finish coat can be troweled smooth, hand-textured, floated to a sand finish or sprayed. Originally, the lath material was strips of wood installed horizontally on the wall, with spaces between, that would support the wet plaster until it cured. This lath and plaster technique became widely used. In exterior wall applications, the lath is installed over a weather-resistant asphalt-impregnated felt or paper sheet that protects the framing from the moisture that can pass through the porous stucco. Following World War II, the introduction of metal wire mesh, or netting, replaced the use of wood lath. Galvanizing the wire made it corrosion resistant and suitable for exterior wall applications. At the beginning of the 21st century, this "traditional" method of wire mesh lath and three coats of exterior plaster was still widely used. In some parts of the United States with a warmer climate (like California, Nevada, Arizona, New Mexico and Florida), stucco is the predominant exterior for both residential and commercial construction. Stucco exterior (with wood frame interior) became a popular alternative in the southwestern United States during the 1970s, as the masonry labor costs for adobe rose.

Sculptural and architectural use

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