Resurfacing a damaged slab

Concrete Construction, August, 2002

Q. Shortly after my slab was poured, there was a thunderstorm. The contractor covered the wet concrete to protect it from the rain. The next day there were marks from the rain, the plastic sheeting, and some light footprints. As years have passed, every time I see the slab it bothers me that it needs to be repaired. What can I use to resurface the affected area?

A. First, the slab doesn't need to be repaired. These cosmetic blemishes will not affect the performance of the concrete. If you want to repair them, though, you could grind down the surface slightly, which would result in exposing some aggregate. Also, you could lightly sandblast the slab, and this would remove the markings, leaving you with a sandpaper-type finish. You would see sand from the concrete mix exposed and possibly a small amount of aggregate. Many people today would see these solutions as creating a decorative finish.

Removing the efflorescence marks left by the plastic sheeting is very difficult. You can try an acidic wash, but probably only a small part of the markings will be removed.

The other possibility is an overlay finish. It can be a sprayable overlay, such as you would see on swimming pool decks, or a stampable overlay. The latter is a thicker application that permits stamped patterns to be installed. Expect to pay approximately $3.50 per sq. ft for the sprayable and about $6.50 or more for the stampable finish.

You could also try tinted sealers, but they may show wear patterns that over time could become a problem.