Stucco comprises fine aggregate (sand) and a cementitious binder, which creates a mortar-like material that’s applied to the exterior of a building. Stucco systems can be  direct applied to a backup material like masonry, CMU, or concrete. They can also be applied to lath, and either integrated with building paper or a water-resistive barrier over a wall assembly or integrated with a water/air barrier and drainage mat over a wall assembly. Each system is designed to accommodate shrinkage, support the cladding system, and manage water with flashings. 

Early 19th century uses of stucco binders were lime-based, including quick lime, lime putty, or hydrated lime. Later, natural cements were used. Around the early 20th century, with the widespread production of portland cements, the most common binder for stucco was portland cement with some lime. Gypsum has also been used in lieu of lime. Other admixtures for workability and curing properties have also been found in stucco mixtures, including fibrous materials, oils, waxes, water-reducers, and air-entrainments.

Stucco is often applied in 2 or 3 layers. The composition and material proportions of stucco layers differ to provide specific properties to the assembly of layers. Scratch coats help in neutralizing the moisture between the substrate and the stucco to limit shrinkage and improve bond. The middle layer(s) provide more stability with additional sand and fibers while limiting shrinkage. The finishing layer provides a mix that can create the desired texture and color. Total stucco thicknesses are generally between 3/4 inches and 1-1/4 inches.  


For successful historic and existing projects, it’s important to prioritize repairs based on the structure’s conditions and project team goals. Project strategies differ per project and can be selected from a variety of repair options.

Refer to our restoration best practices page for additional information, details, and resources. Below, find stucco repair and restoration options for consideration on your project.

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Here are some additional resources that focus on stucco and restoration. For a more comprehensive list of repair and restoration resources, please refer to the restoration page. For additional guidance, contact IMI.


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