Time

Two days

Complexity

Intermediate

Cost

$350

Introduction

The first thing to understand about concrete basement wall cracks is that some are more serious than others.

Cracks running vertically are common, and don't usually indicate structural damage. Horizontal cracks, on the other hand, are serious. They mean your wall is beginning to fail and needs immediate attention.

Traditionally, that attention has come from basement repair professionals. "Don't try to fix horizontal cracks on your own" is the standard advice. My advice, as someone who's successfully repaired vertical and horizontal foundation cracks with the method shown here, is to decide for yourself.

The traditional concrete wall crack repair involves injecting filler epoxy. Problem is, it doesn't provide a strong enough bond. That's why it works great for filling vertical cracks, which aren't likely to get much bigger, but not for horizontal cracks, which often widen over time.

The following repair approach solves this problem so well the finished repair ends up stronger than the surrounding concrete. And it works great for vertical and horizontal cracks. Here, I'll demonstrate the repair process with two concrete cinder blocks to simulate a basement wall crack.

Tools Required

  • Caulking dispenser
  • Eye protection
  • Grinder with masonry-grade cup wheel
  • Hammer
  • Hand broom
  • Hearing protection
  • Mask for nose and mouth
  • Paint roller
  • Paint stir stick
  • Tape measure
  • Wire brush

Materials Required

  • Adhesive epoxy
  • Can of spray foam solvent (optional)
  • Carbon fiber reinforcing strips
  • Expanding polyurethane injection solution
  • Large wooden kebab skewers (5 mm diameter 12 inch length)
  • Plastic injection ports and caps
  • Rubber gloves
  • Surface prep paste

Project step-by-step (6)

Step 1

Identify cracks and install injection ports

  • Try to identify cracks in your basement wall early on. Repair works best when cracks are 1/4-inch wide or less, although this approach will work for cracks up to one inch wide.
  • Put on rubber gloves and eye protection.
  • Use a wire brush to remove any dust, grit and debris on the concrete bordering the crack. If your wall is spalling (flaking off in large pieces), take a grinder with a cup wheel to remove all loose material.
  • Fit a tube of crack prep surface paste into your caulking dispenser. The product linked is the most effective I’ve tried for concrete crack repair.
  • Thread a fresh nozzle onto the tube. Start at the top of the crack if it runs vertically.
  • Dab a thin bead of paste about an inch long onto the concrete where the crack begins, on both sides.
  • Press a plastic injection port (included with the crack prep surface paste we used here) into the paste, centering it over the crack so the port leads directly into it.
  • Repeat the process, installing a port every 18 inches along the length of the crack.

Identifying the crack and Prepping the SurfaceRobert Maxwell for Family handyman

Step 2

Superficially seal the crack

  • Seal the surface by squirting a generous bead of surface prep paste inside the crack along its entire length. Use as much as you need to fill the crack, ensuring the paste extends into the crack and beyond the wall surface.
  • Lay more thick beads of paste on either side of the crack, one to two inches away from it.
  • With a paint stir stick, spread the paste evenly over the crack and the two to three inches of concrete on each side.
  • Cover the base plates of all the injection ports with paste. Be sure to keep the ports themselves open to the crack.
  • Insert a large wooden skewer into each injection port and wiggle it back and forth while the paste is still wet. This ensures the ports will stay open and aren’t accidentally sealed with paste. Remove the skewers right away to preserve the passage.
  • Wait at least 12 hours for the surface prep paste to harden.

Superficially Sealing the crackRobert Maxwell for Family handyman

Step 3

Fill the crack

  • Remove the tube of surface prep paste from your caulking gun and replace it with a tube of polyurethane injection solution with a fresh nozzle.
  • Beginning at the top for vertical cracks and the left for horizontal, stick the nozzle into the first injection port and begin squirting the contents through the port and into the crack. Have a bunch of injection port caps ready.
  • Watch the next port along the crack, 18 inches from the one you’re injecting. The moment you see injection solution fill that second port, remove the tube from the first port and stick a cap in it to prevent leakage. A little solution will still leak out when you do this, but you can scrape it off and clean up after it’s hardened. If you prefer not to scrape it up later, you can clean it up while it’s still wet with some spray foam solvent
  • Repeat the injection process at every port installed along the crack. Continue spraying until you see solution appear at the next port.
  • Wait 12 hours for the polyurethane to expand and harden inside the crack.

Filling The CrackRobert Maxwell for Family handyman

Step 4

Re-prep the surface

  • Break off all injection ports with a hammer.
  • Put on your mask, eye protection and hearing protection.
  • Use a grinder with an abrasive cup wheel meant for masonry to remove the hardened surface prep paste, along with any remaining bits of the broken off injection ports.
  • Continue grinding until the wall becomes a smooth concrete surface. The crack should be filled with surface prep paste and flush with the surrounding concrete.

Re-Prepping the SurfaceRobert Maxwell for Family handyman

Step 5

Apply adhesive epoxy

  • Sweep any dust from around the crack.
  • Load your caulking dispenser with a tube of adhesive epoxy
  • Squirt thick beads of epoxy in a tight zigzag pattern across the crack, going beyond it on each side by about five inches. Do eight feet of crack at a time.
  • Take a paint roller and spread the beads of epoxy so the 10-inch area of concrete spanning the crack is evenly covered.
  • Repeat the process, squirting on more zigzagging beads of epoxy over the stuff you’ve just rolled out. Then roll out the fresh stuff as well. That should be enough to establish a sufficiently thick layer of epoxy.

Applying Adhesive EpoxyRobert Maxwell for Family handyman

Step 6

Apply reinforcing strip

  • Unroll a strip of carbon fiber reinforcing fabric and carefully apply it to the epoxy-covered area. Make sure it’s spanning the crack evenly.
  • Go over the entire strip with your paint roller to press it down firmly. You should see the epoxy squeeze through the fabric. Roll out all this epoxy over the fabric evenly.
  • Squeeze more epoxy onto the fabric in a tight zigzag pattern, then roll it out evenly.
  • Repeat the process of adding epoxy followed by fabric as needed to cover the whole crack.
  • Allow the epoxy to cure over the next 12 hours or so.
  • Congratulations, your concrete crack repair is complete!

Applying Reinforcing StripRobert Maxwell for Family handyman

Note: I tested the strength of my cinderblock “repair” by trying to pull them apart with two full-sized farm tractors. The repair didn’t budge!

trying to pul apart fixed concrete block with a tractorRobert Maxwell for Family handyman

Author
Robert Maxwell
Robert Maxwell is a seasoned carpenter, builder, cabinetmaker, homesteader, stone mason and mechanic. He's been sharing his knowledge through digital and print articles since 2010. Robert lives in a self-built cabin in the woods in Northern Ontario, Canada with his wife and daughter.
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Robert Maxwell