Portland cement-based plaster or stucco is a popular exterior wall cladding used on commercial and residential buildings. Stucco is generally categorized as a one-coat system that incorporates a proprietary, manufacturer supplied basecoat or an ASTM C926 mix that may be a factory-prepared basecoat but is commonly comprised of locally sourced materials (sand, cement, etc.) that are proportioned according to the ASTM standard. The basecoat for a one-coat system is applied at a thickness up to 1/2 inch thick while ASTM C926 basecoats can be up to 3/4 inch thick. Both have an outer layer of finish coat applied over the basecoat.
Regardless of the stucco type, the basecoat is applied to lath (non-metallic or metal-based product) or a solid plaster base, such as concrete masonry unit, concrete, clay brick or tile. While stucco often relies on cavity insulation to provide the buildings thermal insulation, the system can incorporate an exterior thermal insulation layer in which case it is referred to as continuous insulation or CI stucco.