Can stucco be applied over painted walls?
This is a common question that often arises when people are updating older construction. Stucco is a cost-effective finish, relatively easily installed, that improves the appearance and creates a water-resistant wall surface. A painted surface will not typically absorb water and, as such, is a substrate to which stucco will not bond—at least not uniformly.
There are two basic alternatives to covering a painted surface with a new coating of traditional cement stucco.
1) Pressure washing to remove the paint in its entirety, then direct apply a two coat system. It is essential to have a surface that is uniformly absorptive to accept the stucco. In addition, it may be necessary to use a bonding such as Weld-Crete with this approach.
2) Attach paper backed rib lath or install appropriate building paper between wall and attached metal lath to provide a moisture barrier and to serve as a bond breaker. Apply traditional three coat stucco to the metal lath and accessories. In this approach, the idea is to treat the plaster like a sheathed system, using metal lath to support the stucco on the substrate, while completely isolating the stucco layer from the backup with 2-ply 60 minute building paper. This prevents a partial bonding situation, which could set up undesirable stresses in the stucco and lead to stucco cracking.
As the key to stucco longevity is preparation, in this case we would recommend the application of an acrylic primer and synthetic stucco system after a thorough pressure washing.