How To Repair Stucco

Stucco is an old style of siding that is still popular in many parts of the country. Its make-up has changed substantially over the years, however, and this is what complicates patches and repairs. Until the advent of the twentieth century, stucco consisted of a wide variety of natural ingredients depending on the skill and expertise of the plasterer. After the dawn of the twentieth century, plasterers began to use more and more manufactured materials in stucco. Today, stucco is primarily a mix of Portland cement, builders sand, and water. If your home is an older one with a stucco exterior finish, you may need to conduct tests to determine the make-up of the stucco. Hydrochloric or muriatic acid will dissolve lime, for example, where it will not affect stucco made from Portland cement. Once you have determined what the components of your stucco are, you can proceed to make the necessary repairs. Moisture is the major culprit in causing damage to your stucco. Water seepage from the roof or splashing up from the ground gets underneath the stucco-usually through hairline cracks, seams, and joints-and causes bulges, splits, cracks, and holes to develop.

Preparation

Stucco makes a beautiful siding product but it requires careful maintenance.

1. Determine if the damaged area is a vertical crack or a horizontal one. Vertical cracks around chimneys, doors, windows, parapets, and other architectural penetrations may well indicate a problem with the foundation.
2. For repairing small cracks and holes, clean the damaged area thoroughly. Remove any loose stucco.
3. Cut the edges of the damaged area on a slight bevel toward the house with a sharp chisel.

Repairs

1. Inspect the substrate and determine its soundness.
2. If necessary, replace any loose or broken wood lath.
3. Install a piece of tarpaper in the base of the damaged area for waterproofing.
4. You can also use a piece of expanded metal if the original stucco used that as a base.
5. Wet the surfaces of the existing stucco and keep them wet while applying the new stucco mix.
6. Apply a 3/8″ layer of stucco in the damaged area pressing it into the underlayment or substrate.
7. Scratch grooves in the surface of the first layer to provide a key for the second.
8. Let the first layer dry thoroughly for at least one day.
9. Apply a second layer of stucco mix about the same thickness as the first, scratch it, and let it dry.
10. Apply a thinner finish coat of stucco.
11. Texture the finish coat with a soft bristle brush to match the original.

Tips

Do not attempt to repair stucco in warm weather. Wait for a cloudy cool day.

You can buy stucco repair products or mix your own from one part Portland cement, four parts builder’s sand, and water. Do not make the mix too runny.

Keep the stucco wet during the period of repairs.

You can use a masonry caulk product to repair small hairline cracks but usually the repair will show to one degree or another.

Do not repair a lime stucco mix with a Portland cement one. They have different shrinkage rates and will develop new cracks and damage over time.

Consult a professional for help in matching finishes and colors. The older the home, the more necessary this may become.