How to Repair Stucco Cracks (and Which Ones You Shouldn't)

Filling a stucco crack is straightforward. Knowing which cracks are safe to fill is the part that matters — because sealing the wrong crack hides a problem that is still getting worse behind it.

Most cracks in stucco are not emergencies. Cement-based materials shrink as they cure and move with temperature, and fine cracking across a wall face is a normal consequence of that. But stucco cracks are also the main way water gets into a wall that was never built to drain, so leaving them open is not a neutral choice either.

Here is how to do the repair properly, and — more importantly — how to recognise the cracks you should not be filling at all.

First: read the crack

Fine map cracking — a network of hairlines spread across a wall face, none of them more than about 1/16 inch. Almost always shrinkage. Cosmetic, and fine to fill.

Straight vertical or horizontal cracks in a regular pattern — often follow the framing behind or the joints in the sheathing. Usually movement-related and generally fillable.

Diagonal cracks running off the corners of windows and doors. Stop. These follow stress concentration at openings, and they are also exactly where water intrusion is most likely to already be happening. Investigate before filling.

Horizontal cracks at floor line level. Stop. These can indicate structural movement or, on a wood-framed house, shrinkage in a wet band joist. Investigate.

Any crack that reopens after being filled. Stop. The wall is telling you it is still moving or still wet, and filling it a third time changes nothing.

Cracks with staining running below them. Stop. Water has been through this crack already and is inside the wall.

The method, for the cracks that are safe to fill

1. Open the crack. Counter-intuitive, but essential. A hairline has nothing for filler to grip. Run an angle grinder with a crack-chaser wheel, or a masonry blade, along the crack to widen it to roughly 1/4 inch and about the same depth. Aim for a slight V or U profile.

2. Clean it out. Brush and blow out all dust and loose material. Filler bonds to stucco, not to grinding dust.

3. Dampen the surface. Mist the crack and the surrounding area with water. Dry stucco pulls moisture out of a cement-based patch before it cures, and a patch that dried too fast will crack straight back off.

4. Fill. For stable cracks, a cement-based stucco patching compound, worked well into the channel. For cracks that move seasonally, a high-quality elastomeric sealant, which stays flexible instead of cracking. Do not use interior filler or standard decorator's caulk — neither survives outdoors.

5. Match the texture. This is the part that separates a repair from a visible scar. While the patch is still workable, replicate the surrounding finish — a damp sponge, a float, a brush, or a spatter technique depending on what your wall has. Practise on a board first.

6. Cure, then paint. Cement-based patches need several days before they will take paint properly. Rushing this is the most common reason a repair shows through.

What this will not fix

Filling a crack stops water entering through that crack. It does nothing about water entering at an unflashed window head, a missing kickout at a roof-wall intersection, or a wall with no weep screed at the base — which is where the great majority of serious water intrusion in this region actually comes from. If your house is from the 1992 to 2007 window and you have staining, hollow-sounding areas, or interior damage, crack filling is not the project you are looking at.

On historic masonry, ignore all of the above

If your house is solid stone or brick — the older borough and village stock in Doylestown, New Hope, Carversville, Perkasie — do not use a modern cement patching compound on it. A hard cement patch on soft historic masonry closes the wall's drying path, and the trapped moisture leaves through the stone instead, spalling the face off around the edges of the repair. These walls need a lime-based mortar softer than the masonry it covers. It is a different trade, and getting it wrong causes damage that the original crack never would have.

When to call somebody

Cracks wider than about 1/4 inch, cracks with staining, cracks that have reopened, diagonal cracks off opening corners, and anything on a wall you have not had moisture-tested. Crack repair by a contractor generally runs $900 to $5,000 in this area depending on extent and access.

Frequently asked

General information for Central Bucks County, PA homeowners — not a diagnosis, not a quote, and not an inspection. Every house is different, and only a registered contractor or inspector who tests your wall can tell you what yours needs.