Basement Wall Crack Repair
Basement cracks are usually more of a water problem than a structural one. Here's how to deal with cracks in basement walls and floors.
Diagnose before you repair
| Crack | Usually | Repair |
|---|---|---|
| Thin vertical crack in a poured wall | Shrinkage | DIY polyurethane injection if it leaks |
| Diagonal crack from a window corner | Minor settlement or shrinkage | Monitor, inject if it leaks |
| Horizontal crack, or stair-step in block | Soil pressure or settlement | Engineer first, then a structural repair (details) |
| Thin cracks in the basement floor | Normal slab shrinkage | Seal with a flexible concrete crack sealant |
| Floor crack with one side raised | Soil movement or heave | Professional assessment |
Repairing a crack in a basement wall
For leaking, non-structural wall cracks, injection (polyurethane for wet cracks, epoxy for dry ones) is the most reliable fix, because it fills the crack through the full thickness of the wall. Follow our step-by-step foundation crack repair guide. Concrete block walls are harder: water travels through the hollow cores, so injecting one crack rarely solves a leak. Leaking block walls usually need a drainage solution.
Repairing a crack in a basement floor
- Vacuum the crack clean. For cracks wider than 1/4", push in a foam backer rod to about 1/4" below the surface.
- Fill with a self-leveling polyurethane concrete crack sealant (for flat floors) or an epoxy crack filler for a rigid repair.
- Let it cure before putting flooring over it. Under finished flooring, consider a crack isolation membrane.
Floor cracks are rarely structural, because a basement slab usually isn't load-bearing. Water coming up through floor cracks or along the wall-floor joint points to groundwater pressure, which a sealant won't stop.
When water is the real problem
- Water along the wall-floor joint (the "cove joint"), not just at a crack
- Several leaking cracks, or leaks through block walls
- Recurring leaks after heavy rain despite sealing
Start with the outside: gutters, downspout extensions and grading. If that doesn't solve it, get quotes for interior drainage or exterior waterproofing.