In this video, This Old House general contractor Tom Silva fixes a fractured foundation.
Repairing a crack in a concrete foundation
- Fill the void inside the concrete block with triple-expanding foam insulation. Wait 10 minutes for the foam to cure.
- Use hammer and cold chisel to widen crack in wall. Then move outdoors and repeat, widening the crack on the exterior of the wall.
- Use a drill and mixing paddle to mix mortar and water in a 5-gallon bucket.
- Add acrylic bonding agent to the mortar and mix again.
- Use a margin trowel to shave off any cured foam protruding from the wall. Then, use the tip of the trowel to push the foam inside the wall.
- Dampen the wall crack with a wet sponge.
- Use a margin trowel to force mortar into the crack on the interior and exterior wall surfaces.
- Smooth the mortar flat to the wall with a flat trowel. Wait about 15 minutes for the mortar to set up.
- Lightly scrub the mortared surfaces with a damp sponge to create a textured finish.
- Allow the mortar to cure for two weeks, then paint, if desired, with masonry paint.