How To Repair Foundation Cracks in Concrete Walls

Spotting a crack in a basement or crawlspace wall is unsettling, but many cracks are cosmetic or simply let in water. The key is knowing which cracks you can seal yourself and which ones signal a structural problem. This guide covers how to assess, repair and prevent cracks in poured concrete foundation walls.

Which Foundation Cracks Are Serious?

Look at the direction, width and behavior of the crack. Mark the ends with a pencil and the date, and measure the width with a crack gauge or a set of feeler gauges. A crack that grows over weeks or months needs professional attention.

Epoxy vs. Polyurethane: Which Should You Use?

Both are sold in DIY crack injection kits that include surface ports, a two-part paste to cap the crack and cartridges of injection resin. The right choice depends on whether the crack is dry and stable or wet and active.

What You Need

• Concrete crack injection kit (epoxy or polyurethane) with surface ports and paste
• Wire brush, shop vacuum and a cold chisel or oscillating tool
• Caulking gun or the dispensing tool included with the kit
• Putty knife, safety glasses, nitrile gloves and a respirator rated for the product
• Optional: hydraulic cement for actively flowing leaks, an angle grinder for finishing

How To Repair a Foundation Crack With Injection

Step 1: Clean the crack

Scrub loose concrete, paint, efflorescence and dirt from the crack and about 1 inch on each side with a wire brush. Vacuum out dust. The surface must be sound for the paste and ports to bond.

Step 2: Dry or wet the crack per the product

Epoxy needs a dry crack, so let the wall dry or use a heat gun briefly and repair during a dry spell. Polyurethane foam is water-activated and works in damp cracks; some kits recommend misting the crack before injection. Follow the kit directions exactly.

Step 3: Attach the injection ports

Place surface ports directly over the crack, typically about 8 to 12 inches apart, and place one near each end. Use a dab of the two-part paste on each port base to hold it. Spacing ports closer on wider or irregular cracks helps the resin travel.

Step 4: Seal the surface of the crack

Mix the paste and spread it about 1/8 to 1/4 inch thick and 1 inch wide over the full length of the crack and around each port base. This cap keeps the resin inside the crack while you inject. Let it cure for the time listed, often 20 minutes to a few hours.

Step 5: Inject from the bottom up

Start at the lowest port and inject slowly until resin appears at the next port above. Cap the port you are injecting and move up to the next one, repeating to the top. Slow, steady pressure fills the full depth of the crack rather than just the surface.

Step 6: Let it cure and remove the ports

Allow the resin to cure, often about 24 hours, or longer in cool temperatures. Then cut or knock off the ports and, if you want a flat finish, grind or scrape off the surface paste. For smoothing patched concrete surfaces, see how to use a concrete rubbing stone.

Step 7: Monitor the repair

Check the wall after the next heavy rain and again over the following months. A properly injected crack should stay dry. If a new crack forms beside the repair or the patched crack reopens, the wall may still be moving and needs an engineer’s evaluation.

Can You Use Hydraulic Cement or Caulk Instead?

Hydraulic cement sets in minutes, even against running water, so it is useful for plugging an active leak or a tie-rod hole. It is rigid, though, and it only fills the face of the crack, so water often finds a path around it later. Flexible polyurethane masonry sealant can cover hairline cosmetic cracks, but neither option replaces full-depth injection for a leaking crack.

Common Mistakes When Repairing Foundation Cracks

• Smearing patching cement over a leaking crack without injecting it.
• Using epoxy in a wet crack, which prevents a strong bond.
• Injecting too fast, so resin fills only the surface and skips the core of the wall.
• Sealing a structural crack without finding out why the wall moved.
• Ignoring the exterior water problem that pushed water through the crack in the first place.

How Do You Prevent New Foundation Cracks and Leaks?

Water management is the best prevention. Keep gutters clean, extend downspouts at least 4 to 6 feet from the foundation and grade soil so it slopes away from the house. If buried downspout lines back up, read how to unclog an underground gutter drain pipe.

Watch for signs of hidden plumbing leaks near the foundation, too, since saturated soil adds pressure on walls; our guide on how to tell if you have an underground water leak lists the clues. Keep large trees and shrubs away from the foundation and maintain any sump pump with a yearly test.

When To Call a Foundation Professional

Hire a licensed structural engineer for an unbiased assessment of serious cracks, then a reputable foundation contractor for repairs such as wall anchors, carbon-fiber straps, steel braces or underpinning. An engineer’s report also helps when you sell the home, since buyers and inspectors look closely at foundation repairs. Check local permit requirements for structural work.

Frequently Asked Questions