Technique for Repairing Stucco Exterior Walls
Many of the homes using the products are still in existence today and still have the original stucco. Stucco is most often damaged as the result of water from leaking roofs or pipes that causes the wall to be over saturated for extended periods of time. These damaged areas are easily repaired and there are several household items that will help you mimic the look and texture of the existing stucco and keep its historic beauty intact.
- Chip away the edges of the loose or damaged stucco with a mason’s chisel and hammer. Continue chipping the areas all the way down to the wire mesh. Clean the area with a wire-bristle brush to remove any loose dust and debris. Wipe the entire area with a damp rag to pick up any remaining dust.
- Cut a new piece of wire mesh if the old mesh is damaged or rusty. Nail the new piece of mesh into the repair area, using galvanized roofing nails. Spray the patch area with water from the spray bottle.
- Mix a small amount of the stucco mixture according to the manufacturer’s instructions. Do not mix more than you can use in 20 minutes as it will begin dry out and won’t adhere to the wall properly.
- Color-match older stucco by having a professional mix the stucco for you. Alternatively, take a chip of the old stucco to your local paint supply store and ask a sales representative to match the color and tint a gallon of paint for you. For newer homes, check to see if the color mix for your stucco is still being sold at your local building supply store.
- Spread a 1/4-inch layer of the mixture into the hole, using a brick trowel. Do not get the mixture on the existing stucco and immediately wipe away any drips. Scrape the patched area with the edge of the trowel in a cross-hatched pattern. Keep the mixture moist while it cures for 24 hours.
- Mix another small batch of the stucco and apply a second 1/4-inch coat in the same manner. Allow it to cure another 24 hours. Keep the patched area moist during the curing process. In some instances, two coats are enough to fully repair the wall. If not, mix and apply a third coat.
- Match the finish on the new patch to the finished texture on the existing stucco while the final coat is still wet. Use the trowel to create a smooth surface or blot a damp sponge against the wet mixture to mimic stippling. Use a wadded piece of cloth to achieve a random and gentler stipple pattern. Alternatively, use a broom for matching swept or stippled patterns.
The Importance of Weather to Stucco Work and Stucco Paint Coatings
Moisture, humidity, rain, or wet conditions during thin-coat or EIFS stucco work can lead to a subsequent series of failures of the entire installation.
The home shown in our photo (left) was the subject of litigation. We observed that the final stucco had been applied over wet surfaces and in some cases over surfaces that also had been troubled by soil that had splashed-up on the building during rainy weather.
Stucco wall paint failures are also traced to moisture, efflorescence, and failure to adequately clean the exterior and then allow it to dry before painting.
- Temperature during stucco work will speed up or slow down the hydration process that cures the cement in stucco. It is best to avoid application in extremely hot or cold temperatures. In hot, dry, and windy weather, frequent misting will be required on the scratch coat or the installer may need to tape polyethylene sheeting in place for proper curing.
- Direct sun tends to dry out the fresh stucco too fast, so installers should try to follow the shade around the building. Also, retardants are available that can be sprayed on the scratch or brown coat in hot weather to slow down the curing. Sun, heat, and rapid drying conditions can present special stucco application troubles or subsequent stucco paint coating troubles in hot dry climates such as the American Southwest. (Photo at left).
- Cold weather also presents problems. Stucco should not be applied under 40°F, and it should not be allowed to freeze within 24 hours of application. Accelerators can be added to the stucco mix in cold weather, but these can weaken the material, and calcium-based accelerators can lead to efflorescence. Heating the materials and, if necessary, tenting the structure can permit work to proceed in cold, even freezing, weather.
- Cool, moist weather is ideal for traditional stucco wall installations. In humid weather, with relative humidity over 70% or heavy fog, misting is not usually required.
General Guidance for Historic Stucco Repair
A skilled professional plasterer will be familiar with the properties of materials involved in stucco repair and will be able to avoid some of the pitfalls that would hinder someone less experienced. General suggestions for successful stucco repair parallel those involving restoration and repair of historic mortar or plaster. In addition, the following principles are important to remember:
- Mix only as much stucco as can be used in one and one-half to two hours. This will depend on the weather (mortar will harden faster under hot and dry, or sunny conditions); and experience is likely to be the best guidance. Any remaining mortar should be discarded; it should not be retempered.
- Stucco mortar should not be over-mixed. (Hand mix for 10-15 minutes after adding water, or machine mix for 3-4 minutes after all ingredients are in mixer.) Over-mixing can cause crazing and discoloration, especially in tinted mortars. Over-mixing will also tend to make the mortar set too fast, which will result in cracking and poor bonding or keying to the lath or masonry substrate.
- Wood lath or a masonry substrate, but not metal lath, must be thoroughly wetted before applying stucco patches so that it does not draw moisture out of the stucco too rapidly. To a certain extent, bonding agents also serve this same purpose. Wetting the substrate helps retard drying.
- To prevent cracking, it is imperative that stucco not dry too fast. Therefore, the area to be stuccoed should be shaded, or even covered if possible, particularly in hot weather. It is also a good idea in hot weather to keep the newly stuccoed area damp, at approximately 90 per cent humidity, for a period of 48 to 72 hours.
- Stucco repairs, like most other exterior masonry work, should not be undertaken in cold weather (below 40 degrees Fahrenheit, and preferably warmer), or if there is danger of frost.
Directions: Shovel the dry ingredients into a wheelbarrow and blend them with a mortar hoe. Add the acrylic bonding agent, then stir in water, a little at a time, until the mix reaches the consistency of buttercream frosting. Too much water will make it loose and unworkable. Once water is added, the mix will stay usable for 30 to 90 minutes before it starts to harden.
Watch The Weather
Freezing temperatures can ruin wet stucco. Wait for nighttime temperatures that stay above 40 degrees before tackling repairs. Hot, dry, windy weather can also interfere by sucking out moisture the mix needs to cure properly. Work in the shade so the stucco doesn’t dry too fast. Between coats, keep the patch moist by covering it with a plastic sheet.
The alkalis in wet cement can cause burns. So when working with fresh stucco, wear gloves or touch the mix only with your tools, not your fingers. Keep a bucket of water nearby to wash any splashes off your skin.
Finish It Right
No patch, no matter how expertly textured, will match the color of the old stucco around it. To do that, you need to apply a pigmented coating over the entire surface. The patch at this house was covered with a thick, sprayed-on acrylic elastomer that bridges and seals hairline cracks. Other acceptable coatings include concrete paints and stains, mineral paints, lime washes, and “fog coats” of pigmented cement. Whichever coating you use, make sure it’s alkaline tolerant and permeable to water vapor. Otherwise, it will be peeling off in no time.
Stucco can and should be sealed properly to prevent moisture intrusion.
If new, stucco can be sealed with a clear concrete/ masonry sealer, which will penetrate into the stucco and stop moisture entrance. These are typically silicone type sealers. While effective, these finishes will usually need to be redone every 4-5 years. Redoing sealing on a regular basis is what prevents deterioration and damage, which can lead to the need for full replacement.
If the stucco is older and has already developed cracking, an elastomeric coating would be a best choice. These finishes are waterproof, seal hairline cracks, and are extremely pliable and flexible. If cracks develop below these coatings, the finish will stretch and bridge the crack, and help keep waterproof. As importantly, these finishes are microporous; they will breath to allow moisture vapor behind it to properly escape without bubbling and blistering. When properly done, elastomeric coatings can easily last 10 or more years.