The primary disadvantage of exterior insulation and finish systems, also known as synthetic stucco, is that they trap moisture, which leads to rotting wood or gypsum sheathing, and promote mold and mildew growth. Proper installation and incorporated drainage systems minimize the risk of water retention and the associated problems.
EIFS consist of three layers. The first layer is foam board attached to the exterior of the building's walls. The next layer is a mixture of cement and polymer that is reinforced with glass mesh. The outside layer is a stucco-like finish. The three layers bond together tightly to create an airtight and watertight covering. Problems occur when moisture gets underneath the coating through places where it attaches to doors or windows, near the roof line or foundation, or through the stucco itself if it develops cracks.
For best results, EIFS should be applied by a trained professional. Doors, windows and flashings need to be specially sealed to prevent moisture leakage. A comprehensive gutter system that drains away from the building keeps moisture from seeping in at the roof line, and the foam layer should not extend below grade to keep moisture from wicking up from the ground. The gutters must be kept clean and free from obstructions at all times, and adequate drainage should be in place around the foundation of the house.