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A corundum masonry blade grinds through concrete, but slowly. A diamond blade costs more but cuts much faster.
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.
Size up the job first. Before beginning any repair, assess the general condition of the concrete slab. (See “Patch or Replace? ” below) 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.
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.
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.
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:
- 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.
- 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.
- How much are you willing to spend? Material costs for a repair are low. Pros would want to completely replace the slab to insure a high quality result. The cost would be substantial.