Stucco is a material used to cover concrete, brick or cinder block, primarily for exterior construction. Stucco is made of aggregate like sand or cement, binder and water and applied to a surface while it is wet. Often sprayed on, stucco hardens to a solid surface as is dries. Modern stucco often includes acrylic fiber and other synthetic materials that add strength and weather-proofing properties. Stucco stands up to many climates, and can last for decades. Stucco that has cracks, holes or other damage can be repaired by spraying on new stucco.
Examining Old Stucco
Stucco must be applied to a surface where a bond can be created. New stucco can be sprayed on existing stucco if a solid bond can be established. Old loose or dirty stucco will not hold any type of stucco repair, whether it is sprayed on or applied in any other manner. Before spraying new stucco over old stucco, check the existing stucco for major cracks and hollow spots. Cracking can be identified with visual examination. Hollow spots can be located by tapping the old stucco lightly with a hammer and listening for the dull noise caused by a void.
Repairing and Cleaning Old Stucco
Fill major cracks in old stucco by hand. Use an approved stucco mix. Hollow spots in old stucco should be chipped off all the way to a solid edge and hand-patched. The entire surface of old stucco should be cleaned with a stiff brush to remove dirt, contaminants and debris, as well as any flaking stucco. Use a hose and scrub brush to clean stucco. For heavily soiled stucco, a pressure washer should be used before applying new stucco. Let the old stucco surface dry completely.
Surface Prepping Old Stucco
Before applying new stucco, you must apply a bonding agent. A bonding agent is a liquid that bonds any stucco to the substrate. Apply the liquid bonding agent with a roller or brush over the repaired and cleaned old stucco. Refer to the manufacturer's specifications, which usually state that the bonding agent is a "one time re-emulsifying bonding agent." This means that after the bonding agent dries, it will reactivate and bond the old stucco with the new wet stucco. A bonding agent can only be activated once after drying, or it will need to be reapplied. Follow the manufacturer's specifications for product specific application and coverage of the approved bonding agent. Apply only the amount of bonding agent that can be sprayed that same day with new wet stucco. If the bonding agent is not covered the same day it is applied, dew and overnight air humidity will actually activate the bonding agent and render it useless.