Cement sidewalks can provide a nice looking addition to a home. But they aren't just attractive; they also add value to a property. Unfortunately, a characteristic of cement many people aren't aware of is that it's porous and it will absorb water. Over the seasons, water can get into the surface of a cement walkway and with melting and freezing cycles, the moisture can actually cause cracks in the cement. Luckily, fixing cracks in a cement sidewalk isn’t a difficult job, well within the skill set of most homeowners, and the tools and supplies are readily available at your local home store.
Fixing Small/Hairline Cracks
A small crack (anything less than 1/4") is really straightforward to repair. You can fill the crack with premixed concrete crack filler that comes in tubes similar to caulking, or by mixing up a paste of Portland cement and water. No matter what you're going to use to repair the crack, the first step is to clean out any dirt or other mess that's in the crack. Spray water into the crack and use a stiff broom to clear it out. If you're using a tube of crack filler, follow the manufacturer's directions about how to use the product. In general, you insert the tube into a caulking gun, cut off the tip of the container, and fill the crack up to overflowing. Then you scrape the surface smooth and let it set up as directed by the manufacturer. You may need to fill the crack a couple of times as the filler might settle.
If you're going to use your own mixture of Portland cement and water, it's a good idea to soak the cement around the crack with your hose so the cement is damp when you go to repair the crack. This extra moisture will stop the surrounding dry cement from literally pulling water out of the patching cement. Prepare your cement mixture so it has the consistency of a thick paste. Use a putty knife to force it well down into the crack and then smooth the surface. Leave the repair alone for a couple of hours, then spray it lightly with water and cover the patch with a plastic sheet. Once a day for the next two or three days, remove the plastic sheet and lightly spray the patch. Keeping it moist will allow the cement repair to dry slowly (cure) and solid.
Fixing Larger Cracks
If your walkway has a larger crack, you can repair it with a similar process, but there are a couple of extra steps involved. Once again, start by cleaning out the crack using the stiff broom and a hose, or even a pressure washer, to flush all the dirt out. Your next step is to widen the base of the existing crack to help hold your concrete patch in place. Use a cold chisel and a hammer to chip out concrete along the bottom edges of the crack—you want to end up with an inverted "V" shape with the sides of the crack widening out at the bottom. Clean out any concrete chips or dust and thoroughly soak the crack with your hose (here again, you want the concrete around the crack to be damp but don’t leave any standing water in the crack). It's a good idea to apply a concrete adhesive to the walls of the crack so the new concrete will bond solidly with the old.
Paint the adhesive along both sides and the bottom of the crack with an old paintbrush and let it sit for a few minutes until the adhesive becomes tacky. Apply your concrete patching mixture with a metal trowel and be sure to pack it tightly into the expanded crack. Smooth the surface and allow the patch to dry for a couple of hours. After the patch has dried for a while, spray the area lightly with your hose and cover with a plastic sheet, removing it once a day to dampen the patch. After four days you can remove the plastic and expose the now cured concrete to the elements.
Patching Holes in a Concrete Sidewalk
If the hole is small and shallow (less than 1/4") all you will need to do is clean it thoroughly and wet the edges, then add and level cement patching material. Be sure to cover the repair and keep it moist while it cures just like your crack repairs. If your sidewalk has a large deep hole (say 1/2" or more) you should follow the undercutting process described above (widen out the bottom of the exposed concrete with your cold chisel so the patch will actually get under some of the existing concrete). In addition, you should also fill the bottom of the hole with sand or gravel that you tamp down solidly to give your patch a firm base. Wetting the sand before tamping it will help to give you that solid base.
An alternative product that can be used instead of filling with sand and topping with patching material is latex cement. It's made up of two components: Portland cement and a latex binder that you mix together to form a quick-setting, durable cement. Latex cement is sand-based (no gravel) so it's easy to trowel smooth. In shallow holes (1/4") just use your metal trowel to pack the latex cement into the hole and level the surface. On deeper holes, apply the latex cement in layers of about 1/4 to 1/2-inch and allow it to set up before applying the next layer. Once again, keep the patch moist for a few days while it cures.
As you can see, repairing cracked or damaged sidewalks isn’t a difficult job; the patch just requires a little maintenance or TLC for a few days. While it might be tempting to not keep the repair moist while the patch cures, don't try it. If the new cement doesn't get the chance to properly cure, it will quickly break down and you'll be right back where you started, if not worse.