Concrete Spalling
moderate 2–5 h
Tools: hammer and cold chisel, wire brush, shop vacuum, margin trowel, bucket, safety glasses · Materials: concrete patching compound or vinyl-modified patch, bonding agent, penetrating sealer
Steps
- Tap around each spall with a hammer: a hollow sound means more surface is about to come off — chisel back to solid, ringing concrete.
- Square up the edges of the patch area so the repair has a shoulder to hold, then brush and vacuum the dust out.
- Brush on a bonding agent and, while it is tacky, press a stiff patching compound in with a trowel, slightly proud of the surface.
- Feather the edges, match the broom texture, and cover the patch with plastic for two days so it cures slowly.
- Once every patch has cured for a month, seal the whole slab with a penetrating sealer and avoid deicing salt for two winters.
- Fix what fed the water: a downspout emptying onto the slab, a low spot that ponds, or a sprinkler that hits it every morning.
Stop and call a pro if
- spalling exposes rusty rebar — the steel is expanding and lifting the concrete, which needs a structural repair
- the spalls are on a step, a balcony or a garage slab edge that carries load
- the damage covers most of the surface rather than a few patches
What a pro does that you can't
A concrete mason removes the surface to sound material, treats exposed rebar, and applies a polymer overlay or a new wear course that bonds and lasts, rather than a patch that pops next spring.
DIY cost: $30–100 in patch, bonding agent and sealer