Cracks in foundation wall
Tools: ruler or feeler gauges, pencil and phone camera, flashlight, wire brush, caulk gun · Materials: crack monitor or plaster tell-tale, hydraulic cement or a polyurethane injection kit for a stable vertical crack
Steps
- Classify the crack: a vertical or slightly diagonal hairline in poured concrete is shrinkage; a horizontal crack, a stair-step crack in block, or a crack wider at the top than the bottom is movement.
- Measure the width and mark the ends with a pencil and date; fit a tell-tale or a dab of plaster across it and check monthly.
- Look for water: a damp streak or efflorescence along the crack means it is the water's way in even if it is structurally harmless.
- For a stable, narrow vertical crack in poured concrete, brush it clean and seal it from inside with hydraulic cement or a polyurethane injection kit, following the kit's port spacing.
- Fix the outside: extend downspouts, regrade the soil to fall away from the wall, and keep sprinklers off the foundation.
- Recheck after the next wet season; a sealed crack that stays sealed and stops weeping is done.
Stop and call a pro if
- the crack is horizontal, stair-stepped, wider than 6 mm (¼ inch), or the wall bows inward
- the crack is widening between checks or new ones are appearing
- doors and windows upstairs have started sticking, or floors slope
- the foundation is block and the crack goes through the blocks rather than the joints
What a pro does that you can't
A structural engineer tells you whether it is cosmetic or structural, and a foundation contractor installs carbon-fibre straps or wall anchors for a bowing wall, or piers for a settling footing, before anyone seals it.
DIY cost: $10–30 for hydraulic cement; $60–150 for an injection kit