If your concrete driveway and steps look like a scene
from a vintage World War II movie, it’s time to strap on your dust mask,
arm yourself with a chisel and a trowel and fight back. Don’t let that
broken corner, hairline crack or crumbling surface defeat you. A repair done
properly will extend the life of your concrete if you catch the trouble early
enough. This article will show you how to create a durable concrete patch to
fix two of the most common problems: spalling and broken
corners.
(“Spalling” is the mason’s term for
concrete that’s pitted or chipped, as in Photo 1.)
We won’t deal with the other common problem, cracks. You can repair them exactly as we show here, but they’ll most likely return unless you can stabilize the concrete slab to prevent the movement that caused the cracks in the first place.
Concrete Repair is For Everyone
Concrete is hard stuff, but don’t let that intimidate you. With the proper tools and techniques we show in our photo
series, even a novice can make a durable patch, first try. Sawing concrete with a special masonry blade (opening photo) may be new to you, but if you’ve handled a circular saw, you’ll quickly get the hang of it. It’s less hazardous than sawing wood. However, the blade kicks up an incredibly thick cloud of abrasive dust, so be sure to wear goggles to protect your eyes, ear protection, gloves and a dust mask, as well as old clothes.
TIP
Click image to enlarge.
You’ll raise an impressive dust cloud when sawing, so close up nearby windows and doors. Otherwise, you’ll be housecleaning, too!
Size Up the Job First
Before beginning any repair, assess the general condition of the concrete slab. (See “Patch or Replace?”) Sometimes
the best strategy is to break out an entire section and repour it with new concrete rather than patch it. Patching works best for local damage in otherwise sound concrete.
If this is your first concrete repair project, allow about a half day to pick up materials and complete two to three patches. It took us about four hours from start to finish to complete the two repairs we show here.
Complete the job during comfortable working conditions, ideally in dry weather with a temperature between 50 and 80 degrees F. Both you and fresh concrete happen to agree on this one. Fresh concrete is easiest to handle and hardens best (a process technically called “setting” and “curing”) in this temperature range. Colder weather lengthens the setting time; freezing temperatures can ruin the concrete. Hotter weather causes faster setting and drying; the slab may harden before you can smooth it. Or the surface can dry too fast and not harden properly, eventually causing it to spall. In hot weather, work in the cooler mornings or in the shade.
TIP
Spend $20 to repair the damage yourself or pay a pro $300 to $400 to replace this simple slab.
To Repair Spalled Areas
The key to a lasting repair is to make a saw cut around the perimeter of the damaged area, cutting back to solid concrete. The cut
should be at least 3/8 in. deep: Most repairs that fail do so because the patch is too thin at the edges and breaks off. Set a masonry blade (see below) at a 5-degree angle so the cutout is slightly wider at the bottom than at the top. This helps “lock in” the patch (Photo 1). Slowly guide the saw through the concrete. The masonry blade grinds a groove, so don’t put a lot of pressure on the saw; let the blade do the work. Cut about 1/4 in. on each pass.
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.
Click image to enlarge.
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 (Photos 2 and 3), 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.
