How to Patch Chipped and Pitted Concrete Sidewalks and Stairs (page 2 of 3)

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Assessing the Damage and Basic Techniques

Patch or Replace?
Should you patch your old concrete or completely tear it out and repour it? While there’s no hard and fast rule, here are some tips to guide your decision:

1. Assess the Severity of the Damage.
If your driveway is full of spalled areas and broken edges, the surface is probably severely weakened. It’ll continue to deteriorate, and chances are the patches won’t last.

Call in a concrete contractor (Yellow Pages under “Concrete Contractors”) to help you assess the situation and ask for a price on complete replacement. But keep in mind that contractors are in the business of selling concrete. With their labor costs, it’s usually cheaper for them to replace than repair. We had trouble finding a contractor who would even do patching.

2. Is Appearance Important?
A patch will be lighter-colored than the old concrete. Even after weathering for a few years, the new patch will probably still stand out. One way to hide the patch is to stain the entire surface to blend the old with the new. But you’ll have to renew the stain periodically.

3. How Much Are You Willing to Spend?
We spent $20 in materials to repair the damaged areas shown in this story. Pros would have charged $300 to $400 to replace this simple 6 x 6-ft. porch slab. A $3 Corundum masonry blade grinds through concrete slowly. A diamond blade ($75) cuts much faster.

A diamond grit blade can cut the concrete about five times faster than a masonry blade, and it won’t wear out as fast. But it also costs more ($75 vs. $3). The extra cost is worth it if you have more than about 10 ft. of concrete to cut. Or save money—and time—by renting a diamond blade (about $15 a day, plus wear fee), or a concrete saw with diamond blade ($50 per day, plus wear fee).

Once you’ve cut and thoroughly cleaned loose concrete from the repair area, moisten the area with a wet sponge before packing in the concrete mix. Don’t leave standing water in the patch area; use just enough to dampen the old concrete and help it bond to the new.

Safety First
Wet concrete is highly alkaline and can cause severe burns to bare skin. Immediately wash off any that gets on your skin with cool water.

The Recipe for a Strong Patching Mix
For your patching mix, use either a prepackaged sand mix or concrete mix, depending on the depth of the patch. (See “Use the Correct Patching Mix”) Each 60-lb. bag makes about 1/2 cu. ft. of concrete, enough for a 2-in. thick patch about 1 ft. wide by 3 ft. long. Estimate the volume of patching material by multiplying approximate length, width and thickness (in feet) to arrive at cubic feet, and buy a bit more than you think you’ll need. At only $2.50 per bag, it’s cheap enough to buy extra. Better to have too much than to fall a few scoops short!

Mix it with water and acrylic fortifier, following the mixing directions on the package. The fortifier strengthens the new concrete and helps it bond better to the old concrete. The mix should be just wet enough to hold together when it’s troweled into the repair. Don’t add too much water. It’ll result in weaker concrete.

We used a normal sand mix, which sets hard enough to walk on in about a day or two. It continues to cure and harden for weeks. If you have to use the area right away, you can buy a special fast-setting concrete, which hardens in about an hour. It costs about twice as much and you won’t have as long to spread and smooth it, so stick to the regular mix when possible. Most building supply dealers that carry regular concrete also carry the fast-setting type.

Pack the Repair Mix Firmly
After mixing the concrete, pack it firmly into the repair area using a wood float, the tighter the better. Mound the mix so it’s slightly higher than the old concrete. Then immediately level it even with the old concrete using a straight board.