Published On: Fri, Nov 3rd, 2023

Can I patch and paint my damaged concrete porch?

Can I patch and paint my damaged concrete porch?
Can I patch and paint my damaged concrete porch?


Q: When we added handrails to our front entry last summer, the contractor had to extend the bottom steps to meet code requirements for the rail supports. The new concrete isn’t the same color, so I would like to paint the entry. The older concrete was resurfaced a few years ago with what looks to be a softer material. As I was power washing the walkway, pieces of the resurfaced material gave way, exposing the original concrete. Should I patch where the power washing pulled up the resurfaced material before painting, or should I resurface all of the concrete to one color?

A: It’s hard to get a concrete resurfacer to stick well for years to old concrete, and coating old concrete with paint is even riskier. So patch the holes and evaluate the color — then determine the best next step. If the patches dry to a color that’s similar to the previous resurfacing material, you might want to simply resurface the lower step and consider the job done.

You could use a concrete patching product to fill the divots, but in this case it’s smarter to use a resurfacing material, such as Rapid Set NewCrete ($26 for a 25-pound bag at Home Depot). Patching with a resurfacer allows you to evaluate how well the color matches. It’s possible to tint resurfacers, but to achieve a good color match you would probably need to prepare numerous test samples, then figure out an accurate way to scale up from a test sample of just a few tablespoons to make the same color with a much larger amount. So just patch with the resurfacer in the color that the manufacturer created.

Concrete resurfacers are basically Portland cement, sand and polymers. You add water, as with any concrete mix. The polymers make the new layer more durable and better at bonding to the old concrete. The size of the sand grains determines how thin the coating can be; a general rule with concrete is that the largest particles should be no bigger than one-fifth the thickness of the final layer. Most resurfacers contain very fine sand because they are designed for applications as thin as 1/16 of an inch. But for patching holes, where the edges help contain the patch, the material can be up to ½-inch thick.

Before you patch, scrub the divots with a wire brush to remove any loose sand grains and grime, then rinse thoroughly. While the concrete is still wet (or after re-wetting it if it has dried), mix a small amount of resurfacer with just enough water to make a clay-like putty that you can push into the divots. Use a plastic putty knife or even a gloved hand. Scrape the patches flush with the surrounding concrete. To make the texture match the surrounding surface, lightly brush with an old toothbrush or other tool.

NewCrete is considered self-curing, which means you don’t need to keep it damp as it cures. But read the instructions on whatever product you buy; some resurfacers need to be misted with water for 24 hours or more to harden well because the chemical reaction that cures concrete stops when the mixture dries. For a small job like yours, a spray bottle would work well. For larger projects, use a hose with a nozzle that has a mist setting.

Once the patches dry completely, evaluate the color. If they blend in fairly well, you might want to skim-coat just the whole lower step with the resurfacer. It would save you from having to deal with tricky details, such as masking around the door trim and what appears to be a drain in the center of the entryway. But if the patches don’t blend in, decide whether to resurface the entire entryway or paint. There isn’t a significant reason to resurface everything and then paint. Just do one or the other.

You mention that the earlier resurfacer seems to be softer than regular concrete. That’s an anomaly — resurfacing products typically achieve strengths equal to — or even slightly above — standard concrete mixes. The power-washing might be the culprit; using a nozzle on a hose is safer, especially on exposed edges. Or the installer might have added too much water to the mix to make it easier to spread, or let the topping dry out too soon. The weird thing about water and concrete is that too much at the beginning is bad — it makes the finished concrete too porous because the excess water leaves little tunnels as it evaporates. But premature drying is also a problem, because it stops the chemical reaction that makes concrete hard.

Whether you opt to resurface just the bottom step or the whole entryway, work on a warm day. The concrete needs to be at least 50 degrees, but not more than 90 degrees. Use no more water than the label recommends, or even a little less, depending on how much of the dry powder you used for patching. Apply with a squeegee. When the coating begins to harden, lightly sweep in one direction to add a little texture.

If you decide to paint, beware that it is likely to stick fine where there is a roof overhead, but it could peel where it is exposed to rain and snow (for example, on the lower step, if that’s not under a roof).

When paint doesn’t stick well to concrete, sometimes it’s because moisture is coming up through the concrete from below. Test for that by taping down a piece of relatively thick, clear plastic, such as a 3-inch square cut from a reclosable plastic bag. If moisture droplets appear over the next day, avoid painting.

Painted concrete can be very slick, so use paint with anti-slip ingredients, such as Behr’s Anti-Slip Porch & Floor Paint ($42.98 a gallon at Home Depot). Follow all steps listed on the label, including etching and priming.

Have a problem in your home? Send questions to localliving@washpost.com. Put “How To” in the subject line, tell us where you live and try to include a photo.


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