Stucco Over Concrete Block Techniques

Two Stucco Choices

• There are two choices today for stucco on concrete block walls. The first is the traditional three-coat stucco method. The other is a new material called "one-coat stucco." Traditional stucco is Portland cement, sand and water, sometimes with lime added, applied in three coats of varying thicknesses with additional sand in the second coat. One-coat stucco also uses cement and sand but adds fibers and other components so it can be applied in a single coat, although a surface finishing coat is often added.

Preparation

• Preparing the wall is important. It must be clean and free of dust, grime or anything that will interfere with adhesion of stucco. Power-washing is often recommended. The wall also should be slightly dampened before the first layer of stucco is applied. That coat and all subsequent coats also must be "cured" by keeping them slightly damp until the cement fully hardens, 36 to 48 hours for the first coat.

Three Coats

• Traditional three-coat stucco consists of a "scratch" layer, a "brown" layer and a finish coat, all applied to the concrete blocks with a flat mason's trowel. The scratch coat is spread 1/4 to 3/8 inch thick and "scratched" with the notched edge of a trowel or a corn broom to make horizontal ridges. The brown coat has extra sand (the brown) and is spread 1/8 to 1/4 inch thick and smoothed. The finish coat is 1/8 inch (or more) thick, applied with whatever texture is desired.

Colors and Finishes

• A stucco wall can be given a variety of colors and finishes. Pigment can be added to the finish coat to provide color, or stucco can be painted after it dries. A stucco wall can have many types of texture. The stucco can be smoothed like an interior plaster wall. Or it can be given a rough or crinkly texture, or some special finish, like "popcorn," where stucco is pulled up into small peaks which then are slightly flattened with a trowel.

One-Coat

• One-coat stucco is applied and finished much like traditional stucco except that scratch and brown coats are combined. It sometimes is surfaced with a finish coat to provide a desired texture. It can be hand-troweled or sprayed on a concrete block surface with special equipment. The fibers and special chemicals give it extra bonding power.