Foundation Crack Repair
Most non-structural foundation cracks can be sealed for well under $150 with a DIY injection kit. Here's how to choose the right method and do it properly, and when not to try.
First, make sure it's a DIY crack. Don't seal horizontal cracks, cracks wider than 1/4", cracks that are growing, or cracks where one side is displaced. Those need the cause diagnosed first. Sealing them only hides the movement. Unsure? Use the Crack Checker.
Polyurethane vs. epoxy injection
| Polyurethane foam | Epoxy | |
|---|---|---|
| Best for | Leaking, non-structural cracks | Dry cracks where strength needs restoring |
| Works on wet cracks | Yes. It reacts with water and expands. | Poorly. The crack should be dry. |
| Flexibility | Flexible, tolerates small movement | Rigid, bonds the concrete together |
| Cure time | Minutes | Hours |
| Typical use | Most basement leak repairs | Engineer-specified structural repairs |
For the typical homeowner job, a vertical crack that lets water in, polyurethane is usually the better choice. Use epoxy when an engineer or contractor specifies it.
Tools and materials
- A foundation crack injection kit with surface ports, paste-over sealant and injection resin. Kits are usually sized for about 10 feet of crack.
- Wire brush, shop vacuum, rags
- Caulk gun, putty knife, safety glasses and gloves
How to repair a foundation crack (DIY injection)
- Clean the crack. Wire-brush 1–2 inches on each side, remove paint, efflorescence and loose material, then vacuum.
- Place the injection ports along the crack, roughly 8–12 inches apart, starting near the bottom. Follow your kit's spacing.
- Seal the surface. Spread paste-over sealant along the whole crack and around each port base, leaving the port openings clear. Let it cure as directed.
- Inject from the bottom up. Inject into the lowest port until resin appears at the next port up, cap the first port, then move up. This pushes air out and fills the full depth.
- Let it cure, then cut off the ports. If you want a smooth finish, scrape or grind off the surface paste.
- Mark and date the ends of the old crack, so you'll know if new cracking appears beside the repair.
What not to use
- Hydraulic cement or mortar smeared over the surface: it seals only the face of the crack and usually cracks or pops out again.
- Silicone caulk: poor adhesion on damp concrete and no depth.
- Exterior-only patching on a wall you can reach from inside. Interior injection fills the crack through the whole wall.
Fix the cause too
Most leaking cracks get worse because of water outside. Clean the gutters, extend downspouts at least 4–6 feet, and make sure the soil slopes away from the house. These cheap fixes protect the repair.
When to hire a professional
- The crack is horizontal, stair-stepped, over 1/4", growing or displaced
- Several cracks leak, or there's water where the wall meets the floor (that's usually a drainage job)
- You want a transferable warranty for resale
See foundation crack repair cost for typical professional prices.