Q: A corner of our concrete porch has chipped off. Is there any way to repair this without replacing our entire porch?
McLean, Va.
A: It’s definitely possible to patch chipped concrete, even in a situation like yours, where the concrete isn’t supported underneath. However, the patch might not dry to the same color and texture. So would you wind up with something that looks better? Or worse? You might want to mix a small amount of patch material, press it into a simple form, such as a tuna can, let it dry and then decide. Or you could plan on patching the corner, then recoating the entire porch with a thin concrete mixture that would give everything a uniform look.
To get a concrete patch to stick, it’s often possible to brush on a concrete bonding adhesive, a polymer similar to white glue, then fill the gap with a mixture of Portland cement, sand and water. But for a vertical patch, like what you need, it works much better to skip the paint-on bonding adhesive and instead use a patch material that contains Portland cement, sand and dry polymers that are activated when water is added, said Steve Witowich, who staffs the technical-advice line for Quikrete, which sells concrete mixes and additives.
The company makes three products that would work: Quikrete FastSet Repair Mortar, Quikrete Polymer Modified Structural Repair and Quikrete High Performance Cement. Products from other manufacturers would also work, but check the labels to ensure you’re buying a product intended for structural repairs up to several inches thick, not for skim-coating a surface.
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When choosing a product, consider how much patch material you’ll need. Some products are sold only in 20-pound pails or 50-pound bags, but Quikrete FastSet Repair Mortar comes in packages of as little as three pounds ($7.98 at Lowe’s). Although it’s more economical to buy in larger quantities — a 20-pound pail of this same product costs only $12.98 — the prospect of not having leftovers might make the smaller package a wiser choice for you.
For a small project like yours, you don’t need to invest in a masonry trowel or the type of edging tool that the original concrete contractor probably used to round over the top edge of your porch. An inexpensive, plastic putty knife should work fine. But you don’t want concrete mix on your skin or in your eyes, so wear rubber gloves and safety glasses. Using a disposable respirator is generally wise when mixing concrete, but if you’re dealing with only a tiny amount, the risk should be minimal.
Polymer-modified patch materials tend to be quick-curing, which means you might have only 10 to 20 minutes of working time. So before you add water, make sure all the preparation is done. Use a stiff-bristle brush or wire brush to dislodge any loose particles, wash and rinse the concrete, and rig up a simple form to support the lower edge of the patch while you shape the sides. A board or piece of plywood clamped to the porch overhang would probably work fine. Spray the wood with cooking oil first to keep the patch material from clinging, and spread painter’s tape or plastic over the surrounding brick, so you don’t accidentally smear concrete mix where you don’t want it.
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Quikrete’s three-pound FastSet Repair Mortar comes in a zip-closure bag, which eliminates the need for a separate mixing container. Just break the seal, add 1¼ cups water, zip the bag closed and knead for about three minutes. For other products, read and follow the mixing directions. Avoid adding extra water, because that will weaken the patch. You can, however, give yourself extra working time by cooling the water with a few ice cubes, Witowich said. That might be a particularly wise move if you’re working on a hot day.
As soon as the patch material is fully mixed, press and sculpt it into a smooth corner patch that’s nicely rounded on the top edge. After 10 to 15 minutes, when the mix is stiffening, remove the form and smooth over the lower edge. If you spot any voids where the patch material didn’t fill completely against the mold, add a little bit of the mixture and smooth it over. You can also use a damp brush or sponge to lightly texture the surface, so it’s more like that of the nearby concrete. Follow instructions on the patch material’s label about misting or covering the area while the concrete cures.
Polymer-modified patch materials contain a much higher percentage of Portland cement than the mixture that was used to build your porch, which will make the patch dry to a darker color, Witowich said. To get a lighter patch, it’s possible to add a light-colored concrete colorant. But this type of product is sold mostly to concrete contractors, and the patch probably still wouldn’t match the surrounding concrete. Concrete weathers in a way that exposes some of the sand grains in the original mix.
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To give your patched porch a uniform look, you could coat the old concrete and the patch with a concrete resurfacing material, such as Quikrete Re-Cap ($23.48 for a 40-pund bag at Lowe’s). Mixed to a thick slurry, it’s designed to be applied by a squeegee, brush or trowel.
If patching and recoating seems like too much trouble to repair the small chip, another option would be to simply grind off a little of the rough edge to create a tidier, beveled corner.
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