Stucco Repair: How To Fix Cracks and Blisters

Stucco siding is known for its attractiveness and long-lasting durability. Over time, a stucco surface can develop cracks or holes. Don’t ignore them! By promptly patching cracks and holes, you can prevent them from becoming major issues.

I spoke to two pros to help break down the essentials for DIY stucco repairs: Geoff Walker, who has 47 years of hands-on experience in the trades and a particular skillful touch with stucco, and Drew Mansur, who has an extensive background in the construction trades, property management, and as a building materials supplier.

With their help, we’ve compiled these instructions for repairing and preserving your home’s stucco siding.

How To Repair Small Stucco Cracks

It’s not uncommon for small cracks to appear in stucco siding. Typically starting as hairline cracks, they widen over time. Fortunately, even cracks up to 1/4-inch wide are still considered small and are perfect for DIY repair.

Depending on which material you have on hand or prefer to work with, you can fill these cracks with stucco patch or exterior acrylic caulking.

Clean the area

Lightly brush away any dirt around the crack with a stiff paint brush or nylon brush. You can use a wire brush to clean out the crack itself, but be gentle.

Fill the crack

Geoff Walker’s preferred material for small crack repair is diluted stucco patching material. Use a small putty knife or paintbrush to fill the crack. (You can use a pre-mixed stucco repair mix, which is ready to trowel on, or a conventional stucco repair mix, which needs to be mixed according to the manufacturer’s instructions.)

If you don’t have stucco patch, you can use an acrylic exterior caulk on thin cracks. If the crack is wider than a dime’s edge but less than 1/4-inch, use a sanded acrylic exterior caulk.

Finish

If you use stucco patch, Walker says to “brush away any excess from the sides with a clean wet brush and a bucket of water. This will help to feather in the patch and make it blend more seamlessly.”

If you used caulk, let it dry according to the manufacturer’s instructions, then paint the stucco as needed.

How To Repair Larger Stucco Cracks or Small Holes

To repair cracks over 1/4-inch wide or holes up to two inches in diameter, you’ll need to do a bit more prep work to help the patch adhere properly.

“Large cracks can be patched in much the same way as small cracks,” says Walker, “though you will need more material to get the job done.”

Clean the area

Use a putty knife or awl to scrape loose debris from the crack.

Mansur suggests taking time to ensure the sides of the crack are secure. “It might seem counterintuitive,” he says, but sometimes you’ll need “to widen the crack to give you a better bonding surface — which you can do pretty easily with a chisel.”

You can optionally apply a stucco adhesive at this point. This will improve the seal and maintain the integrity of the stucco.

Fill the crack or hole

Apply a stucco patching material with a putty knife or brush. “It may be easier to fill the crack with stucco that is less watered down than the feather patching batch,” says Walker.

Then, feather it away from the large crack using a clean brush and the more diluted patch.

Add texture

Use a wire-bristled brush to add texture to the patch and match that of the existing stucco. Mansur suggests trying a few techniques to find the best match.

Finish

Once the patching material has dried (follow the manufacturer’s instructions), paint over the patch if desired.

How To Repair Larger Areas of Damaged Stucco

One caution before you start: be sure the damage isn’t due to faulty installation or moisture that’s somehow gotten behind the stucco. For those situations, a patch may just be a bandage. You may need to bring in a pro to troubleshoot the problem and make a permanent fix.

If you have many intersecting cracks or several larger holes, the difficulty of the repair increases accordingly. In addition, much of the repair will depend on how the stucco was originally installed. Was it put on wood or wire lath? What kind of flashing is behind it? What was the root cause of the stucco damage? We can’t address all the possible factors impacting your specific stucco damage, but here are the general steps for repair.

Remove loose stucco

Using a hammer or chisel, remove all the damaged stucco and debris and some undamaged stucco around the repair area.

This is when you can assess the condition of the underlying materials. “Don’t damage the underlying lath or sheathing,” cautions Mansur. If the existing lath is in good shape, being too aggressive at this step can create more work.

Remove damaged lath and paper as needed

However, if the lath and paper are weakened, then remove the lath and cut away the felt paper near the damaged stucco. But leave the lath and wrap behind the good stucco that you removed.

Install new paper and lath as needed

Cut a piece of felt paper to match the size of the area being repaired. Secure it firmly to the studs or sheathing with a staple gun. Make sure it overlaps the wrap on the margins that you left intact. Seal around the wrap seam with acrylic exterior caulk.

Using tin snips, cut a piece of metal lath the size of the repair area. Staple it to the wall or attach it with lath or roofing nails.

Apply the first stucco repair coat

Apply the first coat, called a “scratch” coat, with a trowel. Fill the area with a shallow layer of stucco compound not more than 3/8-inch. “With this first layer,” says Walker, “the goal is to get the stucco to adhere to the wire mesh first and then cure.”

Etch the surface of the stucco material with a putty knife or trowel; this will help the next coat adhere to the first. Let dry according to the manufacturer’s instructions.

“It’s important to follow the manufacturer’s instructions,” says Walker, “or the stucco won’t properly adhere to the structure and the whole thing will just flake or fall off.”

Wait for the stucco compound to dry and cure before starting the second coat.

Apply the second coat

Prepare the stucco mix and apply the second coat, called a “brown” coat, to the area. Etch the surface of the stucco with a putty knife or trowel. Let dry.

“Bring the second coat end-to-end over the whole distance of the patch and up to nearly the final thickness of the original stucco layer,” says Walker.

“Reapply if shrinkage happens while it is drying and curing,” he continues. “It is also critical to keep the stucco moist so that it doesn’t experience too much thermal stress and crack as a result. This can mean hosing the patch down multiple times per day in environments with extreme heat.”

Apply the third coat

Apply the last coat, called the “color” coat, to the patched area. Use a stiff-bristled brush, broom or other implement to create a texture that matches the existing stucco. Be sure to practice your texturing technique before you apply this last coat.

If you’re repairing stucco that has never been painted, use colored stucco mix to match your existing color. If the stucco has been painted, use the same stucco mix you used for the first two coats.

“Make sure to follow the manufacturer’s instructions to the letter,” says Walker, “because each product and situation is slightly different and may affect the final outcome visually or structurally.”

Blisters in Stucco?

If your stucco has bubbles on the surface, take a closer look. The blisters could be in the stucco, or they could be only on the paint. One way to test this is to carefully cut the bottom of the blister and peel it up, checking to see if the bubble includes stucco material. Be ready to patch it with touch-up paint or stucco patch compound.

If you see significant numbers or sizes of blisters, search for the potential for water infiltration.

What NOT to Do When Repairing Stucco

Both of our pros have seen plenty of stucco mistakes over their careers. Here are the most common missteps that are easily avoided.

“Honestly, one of the biggest mistakes you can make when repairing stucco is not cleaning and preparing the surface properly before patching up the stucco,” says Drew Mansur. “If you don’t clean it well, you might find that it won’t bond to the surface or last as long.”

Geoff Walker advises that DIYers not to assume a stucco coat is cured simply because it’s dry to the touch. “Always wait for the manufacturer’s recommended dry and cure time. It isn’t just a suggestion; it is a direction that needs to be followed. If you don’t let patches cure to the degree that the manufacturer indicates, the second coat won’t adhere to the first, and everything will eventually fall or flake off.” He says this issue is especially common when DIYers use a compound accelerator to speed cure times. It seems like a time saver, but it can result in a surface that looks ready long before it actually is.

About the Experts

• Geoff Walker has more than 47 years of experience in the construction and restoration industries. He’s traveled the world while learning and perfecting his skills in the trade and working on projects from residential to commercial and industrial projects. When he isn’t restoring homes for ASAP Restoration, Geoff is fixing up cars and motorcycles in his home mechanic’s shop.
• Drew Mansur graduated from the University of UNSW with a degree in construction management, which led to a career in the construction industry. He is the co-founder and head of growth at TileCloud, Australia’s leading online tile store.