Stucco is a popular wall covering for both exterior and interior walls. Many property owners find it necessary to repair stucco on their building at some point, either because of cracks and weather damage or because of other repairs and modifications to the building. A property owner with basic tools should be able to handle the job. The process involves preparing the area to be patched, applying three layers of stucco patches, texturing the final coat of stucco patch to match the existing stucco as closely as possible, and applying any sealant or paint that may be desired.
There are several steps involved in preparing to patch stucco. The first step involves cleaning — and cleaning out — the area to be patched. Use a hammer and chisel to remove loose stucco from around the patch site, and then clean any dust or debris from the area. Verify that the wire lath and weather barrier paper behind the lath are in acceptable condition; if they aren’t, replace them before applying the stucco patch.
Consider the type of stucco used on the building when planning to repair it. Buildings that were stuccoed in the 18th and 19th centuries were often stuccoed with a lime-based stucco. Portland cement stucco began to gain popularity in the 20th century, eventually replacing the lime-based stucco that had been popular in the preceding centuries. Portland cement stucco is harder than lime-based stucco, and this difference in hardness may cause the repair to crack and fail if the two types of stucco are mixed when attempting to patch stucco.
Stucco patch mix is available from many hardware and home supply stores and is fairly inexpensive. The mix used to patch stucco is available dry or pre-mixed and ready to use. Stucco patches may be applied with a putty knife or trowel. A spray bottle for misting water will also be used when preparing to patch stucco.
The patch site should be dampened with water from a spray bottle before applying the stucco patch. The stucco repair mixture should be prepared according to the manufacturer’s directions once the patch site is ready. The first layer of stucco patch should be approximately 1/4-inch (6.35 mm) to 3/8-inch (9.5 mm) thick and can be applied with a putty knife or trowel. The surface of this layer of the stucco patch should be scored with a putty knife or nail in a diamond-shaped pattern to facilitate bonding with the second layer. The first layer of stucco patch should be allowed to dry for several days before applying the second layer.
The second layer is applied similarly to the first layer. The second layer should also be approximately 1/4-inch (6.35 mm) to 3/8-inch (9.5 mm) thick. The surface of the second layer should also be roughened to facilitate the final layer bonding to the second layer. Some people prefer to let the middle layer dry for several days before applying the final layer, while others prefer to allow the second layer only to set before applying the final layer. The second layer, if it has been allowed to fully dry, will need to be misted with water from a spray bottle before applying the final layer.
The final layer of the stucco patch is applied the same way as the other layers, except it should be no thicker than 1/4 inch (6.35 mm). Instead of roughing the surface of the final layer of stucco patch, it should be textured to match the existing stucco pattern as closely as possible. The stucco patch should be allowed to dry for several days prior to applying stucco sealant and doing any painting. Stucco may need to dry for as long as a year before applying an oil-based paint to the surface.
The manufacturer’s instructions for mixing and applying the stucco patch mix should be heeded. Stucco should not be allowed to dry too quickly when attempting to patch stucco or it will not cure properly. The patched area should be kept cool and shaded if outdoors. It may be necessary to spray the new stucco patch with water from a spray bottle every few hours in warm weather to prevent the stucco patch from drying too quickly. Stucco repairs also should not be done when the weather is cold or is likely to frost or freeze, because this will also prevent the stucco patch from curing properly.