How to patch a cracked sidewalk or concrete patio | The Seattle Times

2022-01-15 09:06:09 By : Mr. Mr. SDGH

Do you have a wide, unsightly crack in your concrete sidewalk, driveway or patio? The concrete may have cracked all the way through the slab, and now one piece is higher than the adjacent piece. These types of cracks can be trip hazards.

Here’s my advice on how you should correct a cracked walk or patio at your home.

Let’s start by discussing what to do if you have a crack and the concrete pieces are in the same plane with no vertical offset. This is the easiest of all repairs, and there’s a good chance you can do this yourself in an hour or so.

I would make this repair using time-tested concrete epoxy. Years ago, it was hard to put epoxy in a crack. You’d have to mix its two thick components — a polyamide hardener and an epoxy resin — and then carefully try to get it into the crack without making a mess.

Now you can purchase a gray concrete epoxy that’s already in a caulking tube. A special mixing nozzle screws onto the end of the tube. As you squeeze the handle of your caulk gun, the two epoxy components are squirted into the nozzle. A special insert within the nozzle blends the components, and by the time they’ve traveled about 6 inches through the nozzle they’re completely mixed.

The epoxy cures to a medium gray color. If your concrete is older and you see the individual sand grains on the surface, you can disguise the epoxy by lightly tamping sand of the same size and color into the fresh epoxy goo. With a little practice, you can do an amazing job of disguising the crack.

It’s important that the epoxy gets at least 1 inch down into the crack. To do this, you almost always need to widen the crack. I use a 4-inch grinder equipped with a dry diamond cutting wheel. Be sure to wear goggles and a respirator so you don’t ingest the concrete dust.

Make the crack 3/8-inch wide and at least 1 inch deep for the best results. (Two inches would be ideal if you can go that far.) Brush out all the loose material and remove the dust so the epoxy creates a strong bond to the two pieces of concrete.

If your concrete crack has produced an offset where one part of the slab is higher than the other, you need to chip away some of the concrete that has lifted up. Once again, the 4-inch grinder with the diamond blade is your best choice. You might want to grind a line about 2 inches back from the crack so your finished repair is as smooth as possible. It won’t be in the same plane because of the offset, but you will still be removing the trip hazard.

The line you grind should be at least 3/4-inch deep. You may find it’s easier to create several parallel grind lines spaced about a half-inch apart that lead to the original crack. These multiple lines allow you to crack out the higher concrete with a hand chisel and 4-pound hammer. You can make faster work of this if you have a rotary hammer drill equipped with a chipping tip.

The goal is to create a shallow trench where you’ll place cement stucco to replace the concrete that was raised up. A trench as shallow as a half-inch will work, but 3/4-inch is better. Once again, remove all loose material and dust from the old concrete.

You’ll need to mix some cement paint as well as the cement stucco mix. Cement paint is just a mixture of pure Portland cement and clean water. Mix it to the consistency of a thin gravy. Keep this paint out of the sun and only mix it just before you intend to use it.

The cement stucco needs to be mixed using coarse sand, Portland cement and hydrated lime, if you can get it. For a strong repair, mix 4 parts sand with 2 parts Portland cement. (If you can get the lime, mix 4 parts sand, 1.5 parts Portland cement and .5 part lime.) Blend these together dry until the mix is the same uniform color, then add water and mix until it’s the consistency of applesauce.

The first step is to squirt some of the concrete epoxy down into the crack between the two slabs. If you have to widen the crack, use the grinder. Once you’ve squirted in the epoxy, immediately spritz the trench with a bit of water. Get the concrete damp, but not dripping wet. Then paint a thin coat of cement paint on the bottom and sides of the shallow trench. Immediately cover the cement paint with the cement stucco mix.

Within a few minutes, the stucco will harden enough that you can use a block of wood rotating in a circular motion to smooth the stucco. When it hardens about two hours later, cover it with plastic for three days and keep the new stucco wet for the entire time.

Tim Carter has worked as a home improvement professional for more than 30 years. To submit a question or to learn more, visit