How do I repair a deeply spalles driveway?
I have an area about 2 ft X 1 ft that is spalling. It is getting deeper, about 1 to 1 1/2 inches. How do I repair this? i.e. type of repair concrete and type of preparation.
Re: How do I repair a deeply spalles driveway?
Spalling occurs when there is either a chemical break-down of the cement holding the concrete together, spot-heating, or from water freezing in crevices which all concrete has. Deep spalling is usually a chemical breakdown usually found with salted roads and driveways, and since the whole pour was homogeneous when laid, the whole area is probably going to follow suit. You can try spot-repairing which sometimes works OK but just as often doesn't as the original pour de-bonds under the patch. Still, it may be worth a try so here's how to do it:
Sweep away all the loose concrete then wire-brush the spalled area and sweep again. Chisel the edges of the spalled area so it's all at least 1/4" deep or close to that. Wet the area thoroughly and let it dry almost completely- no liquid water can remain- then sweep again. Apply a bonding agent ( I use Acryl 60) full strength with a brush wetting the area well. Apply a patch of "sand mix" which is simply concrete without any gravel as you would with any patch. After a day or two (and fully dry weather if working outdoors) apply a concrete sealer which will help prevent future problems. If you're lucky the repair should last a few years, more if the salting is stopped.
If the slab is structurally sound overall and the situation allows, the best repair is a cap of new concrete, prepping without the chiseling just as before. Specify pea-gravel in the mix and pour at 1 1/2" inch or more thickness. Cover the finished concrete to slow the curing as much as you can; if it cures too fast it will have a much nweaker bond. I like to use poly and allow a week to cure for driveways, half that for sidewalks. That should hold up every bit as well as a new standard concrete pour with full-sized aggregate would for as long as the concrete under it remains structurally sound. The edges will be a bit weaker but this is not often an issue- regular vehicle traffic and parking won't cause problems.
With all concrete, if you salt for freezing you should do so as minimally as possible and wash the residue away as soon as temperatures allow.