The short answer
What Causes the Cracks
Stucco is a porous material that soaks up rain. When the wall gets wet, it expands slightly. As it dries, it contracts. This repeated cycle can create stress fractures, especially if the stucco is old or was applied in a single thick coat.
Another common cause is water getting behind the stucco through small gaps around windows, doors, or where the wall meets the roof. That trapped moisture can push against the stucco from behind, causing it to crack or bulge. In colder climates, frequent freeze-thaw cycles can make this worse.
- Hairline cracks from normal drying
- Larger cracks from water pressure behind the wall
- Cracks along corners or edges of windows and doors
- Cracks that follow the lath or wire mesh underneath
- Spider-web patterns from impact or settling
Is It a Serious Problem
Not all cracks are serious. Hairline cracks that are less than a sixteenth of an inch wide are often cosmetic. You can patch them with a flexible caulk or stucco patch. But if the crack is wider, or if you see the stucco pulling away from the wall, water may be getting inside.
Water behind stucco can lead to rot in the wood framing, mold growth, and damage to the interior drywall. If you notice dark spots on the inside walls, musty smells, or peeling paint, you likely have a moisture problem that needs attention.
The key is to find out whether the crack is from surface stress or from water intrusion. A simple test is to press on the stucco near the crack. If it feels soft or moves, you have a deeper issue.
How to Check for Water Damage
Start by looking at the inside of the wall directly behind the crack. Use a flashlight to check for stains, bubbling paint, or soft drywall. Also check the attic and crawl spaces for any signs of water entry.
If you suspect water is trapped, you can use a moisture meter to measure the dampness in the stucco and the wood behind it. That tool can tell you if the wall is still wet days after the rain. You can find these meters at hardware stores or ask a pro to do a moisture check.
Pay attention to the weather. If the crack appears only after heavy rain, it is likely tied to water. If it appears during dry spells, it could be from settling or temperature changes.
- Use a flashlight to look for dark stains on interior walls
- Feel the wall for soft spots or bulges
- Check the attic for wet insulation or wood
- Look for mold or mildew near the crack
- Inspect the exterior for missing caulk or damaged flashing
When to Call the Pros
If the crack is larger than a quarter inch, or if you see multiple cracks in a pattern, it is wise to have a professional assess the situation. A water damage pro can use moisture mapping to find hidden moisture behind the stucco. That helps determine if the water is coming from rain or from a plumbing leak.
If the wall has been wet for a while, you may need structural drying to prevent mold and rot. The pros can set up dehumidifiers and air movers to dry out the wall cavity. They also can inspect the surrounding areas for damage that you might not see.
Can You Patch It Yourself
You can patch small hairline cracks with a high-quality exterior caulk or a stucco repair compound. Clean the crack with a wire brush, remove any loose material, and apply the patch. Let it dry completely before painting.
For larger cracks, you might need to use a bonding agent and a stucco mix that matches the existing texture. But if the crack is from water damage, patching it without fixing the water problem will only hide the issue. The crack will return.
If you are not sure about the cause, it is better to have an inspection first. A pro can tell you if the crack is just cosmetic or a sign of bigger trouble. That way you do not waste your time on a patch that will not last.
- Clean the crack before patching
- Use a flexible caulk for small cracks
- Match the texture for a smooth repair
- Wait for dry weather to apply the patch
- Consider a pro if the crack is deep or wide
Talk to someone now
Call (617) 404-2753 any time, day or night, and describe what happened.
Call Now (617) 404-2753Frequently asked questions
Should I worry about a hairline crack in stucco?
A hairline crack that is less than a sixteenth of an inch wide and does not let water in is usually not serious. You can patch it with caulk. But if it grows, or if you see water stains, treat it as a possible entry point.
Can heavy rain cause stucco to crack even if the wall is new?
Yes, new stucco can crack if it dries too quickly after rain, especially in direct sun. Also, if the stucco was applied too thickly or the base was not prepared well, it can crack. Watch for cracks and patch them early.
How do I know if water is behind the stucco?
Look for dark spots on the interior walls, bubbling paint, or a musty smell. You can also tap the stucco; a hollow sound suggests a void. A moisture meter can confirm if the wall is still wet. If in doubt, have a pro inspect it.