How to Repair Cracked Concrete

Clean the area in and around the damage with a wire brush and broom. Then wash the area with a concrete cleaner and a stream of water.

Use a board as a form by securing it against the side of the area you intend to repair. Place bricks or other heavy objects against the board 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.

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 a bonding agent instead of water or coat the edges of the surface to be repaired with a bonding agent.

Smooth the mixture with the trowel, using the top of the form as a guide.

When the patch has set (see manufacturer's instructions for the patch compound you're using), remove the form and smooth or brush the surface of the patch as necessary to match the surrounding concrete.

Keep off the patched area until it's had time to cure according to the manufacturer's instructions.

Mix vinyl patching compound as directed by the manufacturer and trowel the compound into the area to be repaired. Tamp the mixture to remove any air pockets.

If you use patching mortar instead of vinyl patching compound, either mix it with a bonding agent instead of water or coat the edges of the surface to be repaired with a bonding agent.

Smooth the mixture with the trowel, using the top of the form as a guide.

When the patch has set (see the manufacturer's instructions), remove the form and smooth or brush the surface of the patch as necessary to match the surrounding concrete.

Keep off the patched area until it's had time to cure according to the manufacturer's instructions.

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. Clean the remaining slab edges with a broom.

Set up wooden 2-by-4 or 2-by-6 lumber 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.

Mix your concrete according to the manufacturer's instructions.

Dampen the area to be repaired. Fill the area between the forms with concrete mix. Begin in one corner and work to the middle. Then start in the opposite corner and work to the middle again. Fill until the concrete reaches the tops of the forms.

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.

Tap the sides of the forms to settle the concrete.

Smooth the surface of the concrete with a darby, which is a long wooden trowel, or large float. Work in large half circles from one side to the other and stop when water appears on the surface.

After the water has evaporated, smooth the surface with a trowel.

Allow the concrete to set and 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.

To accurately match the look of the rest of the slab or walk, you may also need to run a concrete edger along the forms and the new concrete. An edger is a special tool that rounds and shapes the edge of a poured concrete surface.

Use a jointer or concrete groover to create a joint in a concrete surface like the lines in a sidewalk. Add joints and grooves as necessary to reproduce the look of the slab or walk you're repairing.

Keep off the patched area until it's 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.