Photo: Lost_in_the_Midwest (Shutterstock)
One of the first things any new homeowner discovers is that a house is basically entropy in building form. From the moment a house is born, it’s dying—eaten by termites, digested by rot, eventually subject to any number of cataclysmic natural disasters. You thought you were borrowing a worrisome amount of money in order to purchase a home for you and your family, but what you actually purchased is a lifetime checklist of repairs.
That includes the exterior of your property—and the sidewalks and curbs. Curbs take a lot of punishment, and one day, you’ll come home weary from work and notice that a curb has cracked, crumbled, or seen a hunk simply vanish in some mystery event possibly involving a wormhole.
If you have a curb that’s broken or crumbling, you should fix it—but first, confirm that you can legally make the repair—in some municipalities, the city owns the sidewalks outside your home and forbids you to do any work, or a homeowners association (HOA) might be responsible. If it falls to you, you can always try to hire a contractor to make the repair, but many contractors aren’t interested in making a small repair to a concrete curb, which means you may very well wind up doing the work yourself. Here’s how to repair your sidewalk curb.
Assess whether the curb needs to be repaired or replaced
The first thing you need to do is assess the state of the curb to determine if a repair—as opposed to complete replacement—is reasonable. If it’s crumbled or broken in just one place and the rest of the curb seems solid enough, you can probably patch it. If large sections of the curb are gone or if there are multiple areas of damage, you might be better off replacing the entire curb. The good news is that replacing the curb is a larger and more expensive job, so attracting a contractor to the work will be easier than with a small repair.
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However, if you decide that the curb just needs a patch, you can do a reasonable DIY repair job.
Clean and prep the area
First, clean out the section that needs to be repaired. You can use forced air or just flush it out with a garden hose, then scrub the area with a wire brush or any kind of stiff-bristled tool. You want to get all the dust and dirt out and make sure all the loose concrete is out of the way. Pro tip: If the damaged area just keeps getting bigger and has an apparently infinite supply of loose material, your curb is probably much worse off than you thought and should be completely replaced.
Once the broken areas are clean, your next step depends on whether you choose to repair the curb with a quick-setting concrete or a sand polymer. Concrete will match the existing curb best but requires a bit more in the way of tools and expertise; a sand polymer is easy to work with even if you’re not the handiest person in the world, but it may not last as long. Note: You’ll see the words “concrete” and “cement” used interchangeably a lot, but technically cement is an ingredient of concrete.
How to repair a curb with concrete
Prime: If you’re opting for a quick-setting concrete like Quikrete’s Quick-Setting Concrete or something like Fusion-Crete, your first step is to prime the surface of the repair spot. Different products have different requirements, so check the usage instructions on the particular concrete you’re using to see what primer they recommend. If you’re totally in doubt, any sort of concrete bond agent is better than nothing. This is key because concrete typically doesn’t bond well to itself, so a primer acts as a “grabby” layer between the remnants of the original curb and your repair.
Mix: Follow the instructions for mixing your concrete product to the letter. Some products will suggest adding something to the mix to increase the strength or durability—for example, Quikrete encourages you to add an acrylic fortifier to your mix when repairing curbs. If the instructions suggest an additive, it’s a good idea to add it. Put on a mask, safety glasses, and some rubber gloves, because concrete wants to kill you. It’s pretty caustic and tends to send clouds of dust into the air just as you’re standing over the bucket breathing in deeply. Trust me on this: If you don’t suit up to mix your concrete, you will get dust in your eyes and life will suddenly seem very precious to you. Alternatively, you could opt for a pre-mixed concrete patch, but these will generally not be as strong. If all you want to do is buy yourself some time, though, they’ll be fine.
Forms: If you’ve got a long section of curb to repair, creating some simple forms will stop your patch from spilling out onto the street. Some plywood and a few bricks can be used to create a simple form—it doesn’t have to be fancy, you just want it to push up snug against the side of the curb so it will hold everything in place while you pack in the repair material.
Repair. Once your repair area is primed and your concrete is mixed, start by packing the concrete into the repair. Using your (gloved) hands and a trowel as necessary, try to work it into every nook and cranny so it can adhere to the primer. Push it in as tight as you can, but keep this initial layer relatively thin—a half-inch or less in depth. Let this sit until it starts to set up (check your instructions to see how long you have to work with), then fill in the rest of the repair with more concrete. Pack it in well, then smooth and shape with your trowel. How pretty you need this repair to look is entirely a personal choice. Be mindful of how much “work time” you have; once it sets, that’s it. Remove the forms, if any, and smooth the sides, as well.
Once you’ve done the repair, consult the instructions. Some products will require you to moisten the area every day for a week or so, some will be good to go immediately.
How to repair a curb with sand polymers
Sand polymers like U.S. Specialty Coatings’ CurbFIX are pretty incredible. They look a bit like unmixed cement, but they act sort of like clay. You don’t need a bonding agent, either. You literally just take a handful of the stuff (wear good gloves—this stuff is also pretty caustic, though dust isn’t a problem as a rule) and jam it into your repair area, then repeat until you’ve filled the void. As with concrete, building a simple form can help hold your polymer in place while you work it, and you should try to pack the stuff as deeply into the voids as possible.
Sand polymers don’t have a set-up time, so you can work at the repair as long as you like. Go to town! Get creative! Or, you know, shape it and smooth it to your heart’s content until it looks perfect. Once you’re satisfied, soak the repaired section in water and the polymer will harden in a few minutes. Once it’s cured, it’s a good idea to paint it with a sealant that’s usually provided.
That’s it! Polymer sand may not stand up the way a concrete product will, depending on how much stress it gets on a daily basis. But its ease of use balances that out—literally anyone can repair a curb using this stuff. Bonus: Once the container is opened, the polymer won’t last too long in a usable state, so you might as well use the leftovers to sculpt a life-size statue of yourself.
No one ever thinks about their sidewalk curbs—until they start to fall apart and your house becomes known as the neighborhood eyesore. A simple curb repair is within just about anyone’s skill set and budget, plus you get to tell everyone you have this adulting thing figured out.
