Stucco is a durable cladding, but it is not waterproof. Water that gets behind it can be slow to dry, and the damage is often hidden until it shows up as stains, soft spots, or rot. This article explains how water gets in, how to recognize damage, what a homeowner can reasonably patch, and when to bring in a professional.
How water gets behind stucco
Stucco is porous and can crack, so some water will always reach the layers behind it. A well-built wall manages that water with a water-resistive barrier and flashing so it can drain out. Problems start when water enters faster than it can drain or dry. Common entry points include:
- Failed or missing flashing around windows, doors, and roof-to-wall joints
- Cracked or dried-out sealant at windows, penetrations and trim
- Roof, gutter, or downspout water running down the wall
- Sprinklers spraying the wall, or a leaking irrigation system next to it
- Stucco running down to soil, concrete, or patios without a proper gap
- Cracks that open to the wall behind
For a look at what sits behind the finish, see residential exterior wall construction layers.
Signs of stucco water damage
- Dark or rust-colored streaks, especially below windows or at the base of walls
- Cracks, particularly at window and door corners
- Stucco that feels soft, crumbly, or hollow when tapped
- Bubbling or blistering paint (see repairing peeling exterior paint)
- Mold or mildew growth on the surface
- Swollen or stained interior drywall, baseboards, or window trim; musty smells
Surface stains and cracks alone do not prove there is rot behind the wall, but they are reasons to investigate.
How to tell if water is leaking behind a wall
- Look inside. Check ceilings and walls near suspect areas for stains, peeling paint, bubbling, or soft drywall.
- Check after rain. Note where the exterior stays dark or wet long after other areas dry.
- Inspect caulk and flashing. Look for gaps, shrinkage and separation.
- Use a moisture meter. A basic meter can give readings on interior surfaces, but results on stucco can be misleading, so treat them as clues rather than proof.
- Hire an inspector for hidden moisture. Professionals may use probe testing, in which small holes are drilled and a probe measures moisture in the sheathing. Because this punctures the wall, holes need to be sealed correctly afterward, so it is best done by someone experienced with stucco.
Water that appears indoors may enter far from where it shows up. A professional leak investigation is worthwhile if you cannot find the source.
Hairline cracks vs. cracks that need attention
Fine hairline cracks are common as stucco cures and the house moves. Many can be filled with a flexible, paintable sealant or patch product designed for stucco. Wider cracks, cracks that keep growing, cracks with stains below them, or diagonal cracks from window corners deserve a closer look (see diagonal cracks in a brick wall for how movement cracks are read). If cracks seem related to foundation movement, a structural or foundation professional should assess before cosmetic repair.
Find and stop the water source first
Repair the roof, gutters, flashing, or sealant first. Patching stucco while water continues to enter only hides the problem and can trap moisture. Fix the cause, then allow the wall to dry before closing it up.
Repairing small damaged areas
For a small, localized area where the underlying sheathing is dry and sound:
- Wear eye protection and a dust mask. Stucco and cement dust irritate eyes and lungs.
- Remove loose or crumbling stucco back to sound material.
- Check what is behind it. Dry, intact building paper or barrier and sound wood are good signs.
- Repair the barrier and lath if needed, overlapping layers so water sheds outward.
- Apply a stucco patch product following the manufacturer’s directions, often in layers, and match the texture.
- Cure and paint with a breathable paint suitable for stucco.
Matching color and texture is difficult, so expect visible patches. If the older house has unknown materials, see the asbestos caution below.
When it is more than a patch (remediation)
If you find wet, soft, or discolored sheathing, rotted framing, mold, or widespread staining, this is a remediation job. Remediation typically involves removing stucco and the damaged materials, drying the wall, replacing rotted components, installing proper barrier and flashing, and re-applying stucco. Rotted framing can be structural, so a contractor with stucco and framing experience, and sometimes an engineer, should be involved. Mold covering a large area is another reason to call a professional.
Very old homes may contain asbestos or lead in some materials. If you suspect this, have materials tested before disturbing them.
Should you seal stucco?
Opinions vary and it depends on the situation. Unpainted, porous stucco is sometimes treated with a breathable water repellent. Painted stucco is usually maintained with breathable masonry paint. The key word is breathable: coatings that trap moisture can make problems worse. Sealing does not fix cracks or flashing leaks, and it should not be done over damaged areas. Follow the stucco manufacturer’s or installer’s advice for your wall.
Does “wet and forget” work on stucco?
“Wet and Forget” and similar products are marketed as moss, mildew, and algae treatments applied to surfaces and left to work over time. They address surface growth, not leaks or structural water damage. Always read the label for the surface you are treating and any plant or runoff precautions, and note that cleaning does not replace repair.
What does stucco repair cost?
Costs vary widely with the size and number of repairs, region, access, and whether hidden damage is found. Minor crack and patch repairs typically cost far less than remediation, which involves removing and rebuilding wall layers. Because of that spread, get written quotes from several qualified contractors and ask what is included, such as moisture testing, framing repair, flashing, and painting. For general cost-planning on larger exterior work, see roofing and siding cost.
When to call a professional
- Staining or soft stucco near windows, with possible interior leaks
- Evidence of rot, mold, or termite damage
- Cracks that widen or follow the foundation
- Probe testing or moisture mapping is needed
- Any work high on the wall requiring scaffolding
A small, dry patch can be a reasonable DIY project. Hidden moisture is not, and early investigation costs less than late repair.