Step 1: Remove loose stucco Use a hammer and masonry chisel to break away the loose stucco. When the bigger pieces have been removed, work around the edges with a paint scraper. Try to leave hard, sharp edges of strong stucco in place as these will form mechanical bonds with the new stucco. Wire brush the area to leave a solid clean surface. Vacuum the area to remove all the loose stucco dust.
Step 2: Prepare new stucco and surface Mix a batch of mortar in a bucket, following the directions that came with the mortar. Mix the mortar until it is the consistency of peanut butter. Use a spray bottle or hose to wet the surface where the new stucco is to be applied.
Step 3: Apply the first coat of stucco Use a trowel to apply the first, or "scratch," coat of stucco. The scratch coat should be about 3/8" thick. Work the mortar up into the edges of the area to be patched. Let the stucco set until it begins to become firm, and then use the trowel to scratch a cross-hatch pattern of lines into the surface. This will form a mechanical bond for the final layer. Allow the scratch coat to set for 24-48 hours or until it is completely dry.
Cut a cross-hatch pattern of lines into the surface.
Step 4: Apply the final coat of stucco Use a spray bottle or hose to wet the scratch layer. Dampen a float with water, and load it with stucco. Wipe the stucco onto the surface with the dampened float. Depending on the pattern of the existing stucco, pull or swirl the new stucco with the float to duplicate the pattern. Allow the stucco to dry for 24-48 hours, and then paint as desired to hide the patch and provide additional protection against the elements.
Wipe the stucco onto the surface with a dampened float.