The Stucco Story

Stucco or render is a material made of an aggregate, 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 concrete, cinder block, or clay brick and adobe.


The difference in nomenclature between stucco, plaster, and mortar is based more on use than composition. Until the later 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 later part of the nineteenth century, Portland cement was added with increasing frequency in an attempt to improve its durability. At the same time, traditional lime plasters were being replaced by gypsum plaster.
Stucco used as an exterior coating on a residential building.

Traditional stucco is made of lime, sand, and water. Modern stucco is made of Portland cement, sand, and water. Lime is added to increase the permeability and workability of modern stucco. Sometimes additives such as acrylics and glass fibers are added to improve the structural properties of the plaster. This is usually done with what is considered a one-coat stucco system, as opposed to the traditional three-coat method.

Lime stucco is a relatively hard material that can be broken or chipped by hand without too much difficulty. The 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 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 used. Today’s stucco manufacturers offer a very wide range of colors that can be mixed integrally in the finish


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.
A stucco face from the ancient Greek city of Ai Khanoum, Afghanistan, 3rd-2nd century BC.

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 is still widely used. In some parts of the United States (California, Arizona, New Mexico and Florida), stucco is the predominant exterior for both residential and commercial construction.

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