stucco

Stucco is a plaster-based exterior wall finish made from cementitious material, aggregate (sand), and water, applied in layers over a substrate such as wood or metal lath, gypsum board assemblies, or masonry. Traditional lime stucco used lime putty with sand, while modern formulations rely on Portland cement with lime or polymer additives to improve workability, strength, and durability. It is commonly applied in a three-coat system: a base coat to embed the lath, a brown coat to build thickness and strength, and a final finish coat that provides texture and color. Some systems are two-coat or use cementitious or elastomeric finishes directly on the substrate.

Stucco is used worldwide on both exterior and interior surfaces but is most prevalent on exterior walls of residential and commercial buildings. It offers durability, fire resistance, and breathability, and can be finished in various textures from smooth to rough. Proper installation and detailing around openings, joints, and penetrations are essential to prevent moisture intrusion. Cementitious stucco is less permeable than traditional lime stucco, and poorly detailed work can lead to cracking, efflorescence, or moisture-related damage in freeze–thaw climates.

Common variants include traditional lime-based stucco, Portland-cement plaster stucco, and synthetic or elastomeric finishes (often marketed as acrylic stucco). Synthetic systems differ in composition and behavior from cementitious stucco and require different installation and maintenance practices. Repairs typically involve patching cracks, re-coating, or re-stucco, with attention to drainage, flashing, and ventilation to manage moisture.