Expert Answers: Patching Concrete

Looking for a way to repair your concrete stairs? HANDY has the answer.

Q: Road salt and about 35 years of aging have damaged the top 1/4 in. of my home’s concrete step and porch. Is there any way to repair this, or do I have to tear it all out and pour new concrete? - Richard A. Riggs, Hymera, IN

A: Early spring is a good time to assess the condition of concrete, especially after winter freezing and thawing have made their mark. The extent of any deterioration will determine whether you repair or replace the concrete. In cases of widespread damage, you’re better off replacing the material; spot repairs would probably offer only a short-term fix.

If you have only small areas to patch, first cut and break away the damaged material. Use a circular saw with a masonry or diamond blade, a maul, a cold chisel, goggles, a dust mask, hearing protection and kneepads. Undercut the edges at a 5-degree angle to help the patch adhere to the old concrete.

Clean out weak concrete, dust and debris using a broom and shop vac. Hose down the area and then remove the excess water, but keep the area moist. Pack in fresh mix and mound it slightly with a wood float. Use a 2x4 and a sawing motion to scrape off excess. You may have to refill and scrape a couple of times until the surface matches the surrounding concrete. Finally, cover the patch with clear plastic for three days; the concrete will be stronger if it is allowed to hold moisture and cure slowly.

If the area that needs to be patched is only 1/4 in. deep, use a topping mix and an acrylic fortifier instead of a concrete mix. But if a corner of the step has sustained damage deeper than 1/4 in., you’ll need to wire-brush the area and build a plywood form to square off the step. Drive a few concrete nails halfway into the old step (see photo), and coat the area with a bonding agent. Then apply the patch mix and make it level with the top of the form. Nails will reinforce the corner and help the new concrete to adhere. - HANDY