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Home > Projects & DIY Toolkit > How-To Articles > Making Simple Concrete Repairs

Making Simple Concrete Repairs

Sure, concrete is tough stuff, but even concrete cracks and crumbles. Eventually, nature has her way. Moisture and temperature extremes make their presence known through damage to concrete floors, walks and structures. Fortunately, you can make simple concrete repairs yourself. The job requires few tools and no special skills, but it does require a strong back. Concrete is heavy, and mixing it is hard work. Still, it's satisfying work if you are up to the task. Lowe's is happy to provide this information as a service to you.

Tools & Materials

Tools

  •   • Small sledge hammer
  •   • Chisel
  •   • Wire brush
  •   • Putty knife
  •   • Shovel
  •   • Trowel
  •   • Darby
  •   • Float
  •   • Edger
  •   • Jointer
  •   • Tamper
  •   • Caulk gun
  •   • Wheelbarrow
  •   • Broom
  •   • Knee pads
  •   • Safety glasses
  •   • Dust mask

Materials

  •   • Ready- or premix concrete mix
  •   • Vinyl concrete patch
  •   • Masonry crack filler
  •   • Quick-setting cement
  •   • Concrete cleaner
  •   • Latex bonding agent
  •   • Gravel
  •   • Sand
  •   • Material for forms (if necessary)

*Tools and materials may differ slightly depending on the type of repair, but this list is representative of those generally used.

Patching Cracks

The technique for patching cracks will depend on the size of the crack.

SAFETY NOTE: Wear gloves, safety glasses, long sleeves and long pants when drilling, hammering or chiseling concrete.

Narrow cracks

  •   1. Remove any loose debris from the crack and surrounding area with a wire brush and broom.
  •   2. Narrow cracks can be filled with a masonry crack filler that comes in a cartridge designed to be used in a caulking gun. Or you can fill the cracks with a vinyl concrete patching compound applied and smoothed with a putty knife. Vinyl concrete patching compound does not require the use of a bonding agent.

Wide Cracks

Undercut the edges of wider cracks for a more secure repair.

  •   1. Use a small sledge hammer and chisel to undercut the edges of the crack as illustrated at right. Undercutting the crack makes it wider at the base than at the surface, providing a mechanical method of "keying" the patch in place for a more secure and permanent repair.
  •   2. Clean the area in and around the crack with a wire brush and broom. Wash the area with a stream of water.
  •   3. Mix vinyl patching compound as directed by the manufacturer and trowel the compound into the cracks. Tamp the mixture to remove air pockets. If you use patching mortar instead of vinyl patching compound, either mix it with bonding agent instead of water or coat the edges of the surface to be repaired with bonding agent.
  •   4. Smooth the mixture with the trowel.
  •   5. When the patch has set (see manufacturer's instructions for the patch compound you are using), smooth or brush the surface to match the surrounding area.

Repairing Edges of Walks and Steps

Undercut cracks in step edges before filling.

If an edge of a walk or step has been damaged, you can restore it to its proper profile. The process is similar to fixing a crack, but requires the use of a form.

  •   1. Remove any damaged or crumbling concrete. Use a small sledge hammer and chisel to undercut the edges of the damaged area as illustrated.
  •   2. Clean the area in and around the damage with a wire brush and broom. Then wash the area with a stream of water.
  •   3. Use a piece of wood as a form by securing it against the side of the area you intend to repair. Use bricks or other heavy objects to hold it in place. The top of the form should be flush with the desired height of the edge. The form will give you a guide for smoothing the patch.
  •   4. Mix vinyl patching compound as directed by the manufacturer and trowel the compound into the area to be repaired. Tamp the mixture to remove air pockets. If you use patching mortar instead of vinyl patching compound, either mix it with bonding agent instead of water, or coat the edges of the surface to be repaired with bonding agent.
  •   5. Smooth the mixture with the trowel, using the top of the form as a guide.
  •   6. When the patch has set (see manufacturer's instructions for the patch compound you are using), remove the form and smooth or brush the surface of the patch as necessary to match the surrounding concrete.
  •   7. Keep off the patched area until it has had time to cure according to the manufacturer's instructions.

Rebuilding Corners

Your form will be a guide for smoothing the patch.

Unless the area to be repaired is very small, rebuilding a damaged corner also requires a form.

  •   1. Remove any loose or damaged concrete from the area to be repaired.
  •   2. Clean the area with a wire brush and broom. Wash the area with a stream of water.
  •   3. Use two pieces of wood as a form by first securing them to each other to form a corner, then placing them against the corner you intend to repair. Use bricks and wooden braces to hold the form in place. The top of the form should be flush with the desired height of the finished corner. The form will give you a guide for smoothing the patch.
  •   4. Mix vinyl patching compound as directed by the manufacturer and trowel the compound into the area to be repaired. Tamp the mixture to remove air pockets. If you use patching mortar instead of vinyl patching compound, either mix it with bonding agent instead of water, or coat the edges of the surface to be repaired with bonding agent.
  •   5. Smooth the mixture with the trowel, using the top of the form as a guide.
  •   6. When the patch has set (see manufacturer's instructions for the patch compound you are using), remove the form and smooth or brush the surface of the patch as necessary to match the surrounding concrete.
  •   7. Keep off the patched area until it has had time to cure according to the manufacturer's instructions.

Repairing Broken Slabs or Walks

Use small pieces of rubble as a bed for your new slab.

Badly damaged slabs or walks are best repaired by removing and replacing the damaged area. This is a larger job than the others addressed in this article, but only because it generally involves more preparation and the mixing of larger amounts of concrete.

  •   1. Using a sledge hammer, break up the damaged area of the concrete into pieces.
  •   2. Remove the larger pieces of concrete from the area and distribute the smaller pieces of rubble to create a firm bed on which to pour the new slab.
  •   3. Clean the edges of the remaining slab(s) with a broom.
  •   4. Set up wooden (2x4 or 2x6) forms along the edges of the area to be repaired. The tops of the forms should be flush with the desired height of the finished slab. The forms will give you a guide for smoothing the new slab area.
  •   5. Mix your concrete according to the manufacturer's instructions.
  •   6. Dampen the area to be repaired.
  •   7. Fill the area between the forms with concrete mix. Begin in one corner and work to the middle. Then, begin in the opposite corner and work to the middle again. Fill until the concrete reaches the tops of the forms.
  •   8. Using a board wider than the repair area, drag the board along the forms to smooth out the surface of the repair area. This is called screeding. Remove any excess concrete that piles up along the front of the board.
  •   9. Tap the sides of the forms to settle the concrete.
  • An edger and a jointer will help you match your repair to the existing concrete.

  •   10. Smooth the surface of the concrete with a "darby" (a long wooden trowel), working in large half circles from one side to the other. Stop when water appears on the surface.
  •   11. After the water has evaporated, smooth the surface with a trowel.
  •   12. Allow the concrete to set, then smooth or brush it to match the existing slab or walk. Insert a trowel between the concrete and the form and run it along the inside edge of the form.
  •   13. To accurately match the look of the rest of the slab or walk, you may also need to run an edger along the forms and the new concrete. A hand edger is a special tool that rounds and shapes the edge of a poured concrete surface. A hand jointer or groover is a tool used to create a joint in a concrete surface-like a crack in a sidewalk. Use these tools as necessary to reproduce the look of the slab or walk you are repairing.
  •   14. Keep off the patched area until it has had time to cure according to the manufacturer's instructions. A slow cure is best for concrete. For this reason, the manufacturer may recommend that you mist the fresh concrete with water and cover it with plastic for at least three or four days.

Tools, products, materials, techniques, building codes and local regulations change; therefore, Lowe's assumes no liability for omissions, errors or the outcome of any project. The reader must always exercise reasonable caution, follow current codes and regulations that may apply, and is urged to consult with a licensed professional if in doubt about any procedures. Please visit our terms of use.

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