Stucco cracking on exterior walls
easy 1–3 h
Tools: wire brush, caulk gun, putty knife, paint brush, coin or feeler gauge, ladder · Materials: elastomeric (flexible) stucco caulk, stucco patching compound, elastomeric masonry paint matching the wall
Steps
- Measure the widest cracks with a coin: thinner than a dime's edge (about 1.5 mm) is curing and weather; wider than 3 mm (⅛ inch), stair-stepped, or clustered around one corner is movement.
- Brush loose material out of hairline cracks and fill them with elastomeric stucco caulk, tooling it flush with a wet finger; do not use rigid mortar, which cracks again.
- For cracks up to 6 mm (¼ inch), widen the crack slightly with the putty knife, dampen it, press in stucco patch, and stipple the surface with a brush to match the texture.
- Paint the patched wall with elastomeric masonry paint — it bridges hairline cracks and sheds water — once the patch has cured for the time on the tub.
- Tap the wall around the cracks with a knuckle: a hollow sound means the stucco has separated from the lath and needs cutting out, not filling.
- Check the roof edge, gutters and window flashing above any crack that keeps returning; water behind stucco is what turns a hairline into a hole.
Stop and call a pro if
- the stucco is soft, bulging or sounds hollow over a hand-sized area or more
- cracks are stair-stepped along block joints or wider than 6 mm (¼ inch)
- cracks run diagonally from window corners on more than one wall — a foundation check comes before any patching
- there are brown stains running down from the crack after rain
What a pro does that you can't
A stucco contractor cuts out delaminated sections, replaces the wet building paper and lath, and reapplies scratch, brown and finish coats; a foundation specialist checks a pattern of returning diagonal cracks first.
DIY cost: $20–60 in caulk, patch and paint