How to repair damaged stucco

While stucco siding requires little maintenance, cracks and other problems should be repaired as soon as they appear.

To repair small cracks caused by hot, dry weather are normal, mist the surface with clean water to minimize or remove them. Follow this step by step approach to repair damaged stucco.

Problem: How to repair damaged stucco with cracks ¾ to 1 inch wide

Solution

To fill cracks this size use products specifically designed for this application; be sure they are non-shrinking. Follow the manufacturer’s directions. Never use traditional or pre-mixed stucco to repair this size crack. The material will shrink, and the crack will re-appear.

Problem: How to repair damaged stucco with cracks larger than 1 inch

Solution

Remove all the cracked stucco with a claw hammer or chisel, being careful not to damage the wood lath. Chip away the stucco until you reach stucco that is still firmly adhered to the lath. Use metal snips to cut and remove wire mesh in the area to be patched.

Cut a piece of builder’s paper to fit the area to be patched, and nail it to the lath. Then add a second layer of builder’s paper over the first. Cut a piece of galvanized metal lath, and nail it over the second layer of paper. Try to get a tight fit between the metal lath and the edge of the existing stucco surface. Using snips with offset handles can make trimming the metal lath easier.

Use a finishing trowel (and more material as needed) to smooth the stucco, until the surface of this coat is ½ inch lower than the surface of the surrounding stucco.

Now you’re ready to apply the stucco. Use a pre-mixed dry stucco product. Add water slowly, and mix to a smooth paste-like consistency. The repair will take three coats of mix – scratch, brown and finish.

If you plan to paint the repaired area, use the same grey pre-mix for all three coats. However, if you plan to add a colored pigment or leave the patch white, use a white pre-mix for the finish coat.

Always wear eye protection and gloves when you work with stucco. If you get any on your skin, rinse it off with water immediately.

Wet the edges around the patch and trowel on a coat about 3/8-inch thick, working from the bottom to the top until it is 1/8-inch lower than the surrounding stucco.

For the finish coat, wet the edge of the patch and trowel on the final layer. Use a finishing technique that matches the texture and pattern of the original siding.

Use a pre-mixed dry stucco product. Add water slowly, and mix to a smooth paste-like consistency.

Depending on the temperature, you’ll have 45 to 90 minutes before the mix hardens.

Never work in temperatures below 40 degrees Fahrenheit and avoid making repairs when it’s hot. High temperatures will cause the stucco to cure improperly by drawing out the moisture too quickly. Between coats, cover the patch with plastic to keep it moist.

Wet the surrounding edge of the existing stucco, so the moisture in the new stucco patch won’t wick into the dry stucco surrounding it. Scoop up baseball sized clumps of stucco and sling it onto the metal lath until the patch is completely covered.

Use a finishing trowel (and more material as needed) to smooth the stucco, until the surface of this coat is ½ inch lower than the surface of the surrounding stucco. When the wet sheen has faded, lightly score (scratch) the surface of this layer with the tip of the trowel. These small scratches will help the next coat of stucco bond to the first coat. Tape a plastic sheet over the patch.

After seven days, remove the plastic, mix a second batch of stucco, wet the edges around the patch and trowel on a coat about ⅜ inch thick, working from the bottom to the top. When the wet sheen fades, smooth the second coat with the trowel until it is ⅛ inch lower than the surrounding stucco. Cover with a plastic sheet.

For the finish coat, wait three days, remove the plastic and mix the stucco. Wet the edge of the patch and trowel on the final layer. Use a finishing technique that matches the texture and pattern of the original siding.

When you complete the finish coat, let the patch cure for seven days. Mist the patch lightly with water every day. When the repair is completely dry, apply a breathable, alkaline-tolerant acrylic paint or stain to the patch.

Problem: Efflorescence

Solution

Efflorescence is a white, dust-like deposit that forms on the surface of stucco. To remove efflorescence brush a solution of white vinegar (or another approved diluted acid solution) onto the effected area, and then rinse thoroughly with water.

If the efflorescence appears near the ground, you may need to dig down along the wall, and seal the stucco that meets the soil. Several sealer products are available for this. If the efflorescence does not appear to be caused by groundwater, look for other sources of moisture, such as irrigation heads.

Problem: Fuzzy growth on surface

Solution

As plants and mulches in flowerbeds decay, the microscopic organisms combine with water and cause mildew to form on adjacent stucco surfaces. To remove mildew on the stucco surface, brush lightly with household bleach and then rinse thoroughly with water.

Synthetic stucco

Synthetic stucco, commonly called EIFS, was used widely in the United States during the 1980s and 1990s. However, the synthetic stucco is no longer used widely because of long-term problems related to moisture. The materials and techniques required to repair synthetic stucco are not the same as for conventional stucco.

–By Bruce Webb