Methods for Applying Stucco on Cement
Cement stucco is an exterior wall covering. It is made of sand, Portland cement, lime and water. To make it more flexible and stronger it may have fibers or acrylics added to it.
Because stucco and cement are made of the same materials the stucco adheres well to a cement wall. Cement is also absorbent and textured. Both of these factors make for a strong bond. If an existing wall has a coating applied to it like paint then it may not bond as well. To see how well a surface will bond with the stucco, simply put some water on the surface of the cement see if it absorbs the water. If it does not then you must prepare the surface by power washing, sandblasting, or acid etching to make it a bondable surface. You can also apply a bonding agent and a last alternative to apply lath with a paper backing to the surface.
Stucco is traditionally applied in a 3-coat process. The first coat, the “scratch” coat, is made up of plastic cement and sand. It is applied with a brush in a pattern that allows for the second layer to adhere to the first. The second layer is not started until the scratch layer had dried. In very arid areas each layer is sprayed with water so that the stucco keeps some moisture in it as it cures. This slows down the drying of the stucco so it has time to chemically harden. If the stucco is not cured properly then it will be more fragile. Next is the brown coat. This coat is made of cement, sand, and lime. It is finished to a smooth surface. This coat must be allowed to dry for a week or so to allow for shrinkage before the finish coat can be applied. The finish coat can be applied with two different materials. A finish coat with a color in the stucco is made of sand in the desired color, cement, and lime. This mixture is troweled over the last coat and can be finished with a finer finish or with a trowel for a textured finish. The other finish coat method uses a colored acrylic. It is applied in various thicknesses and is a quality durable choice.
Many people are now using a 2-coat method that is faster to apply and less expensive. This method skips the scratch coating and begins with the brown coat.
To add to the look of stucco often inserts called popouts. These are set around the windows and corners to add depth and roundness. Foam is cut out and placed around the windows and corners and then it is coated with the rest of the building. There is a newer product that is installed just before the finish coat but the stucco is very thin over the foam and it can become exposed.
When a stucco finish is applied properly it is a long-lasting finish. It can be made distinctive by choosing just the right color and texture.