Q.: While applying curing compound, one of my workers walked on a parking structure deck too soon. He left footprints in the concrete that are very shallow, less than 1/16 inch deep, but still visible. There are many of these footprints in areas of up to 900 square feet, and the owner wants them repaired so they aren't noticeable. Is there any way to do this economically?
A.: It might be possible to remove the footprints by shotblasting the areas containing them. Although this will probably change the color and texture of the treated areas, the overall appearance might be more acceptable to the owner. Production rates for large shotblasting units can exceed 3,000 square feet per hour. Consult a contractor who does surface preparation for floor coatings. You can find a list of some of these contractors in the membership directory of the International Concrete Repair Institute (ICRI). For information about the directory, call ICRI at 703-450-0116.
You could also try patching the footprints, but this will make them more noticeable. It's also difficult, if not impossible, to ensure bond for such a thin repair.
A third, more expensive alternative is to patch the footprints and then apply a thin coating or membrane that will cover the entire affected area. This also will change the color and texture of the treated area and probably require the services of a skilled contractor to apply the coating.
The footprints don't impair the function of the structure, and repair options are likely to leave something just as conspicuous as the footprints. It's also possible that the shotblasting option will open the surface, allowing chlorides to more easily penetrate the concrete. In view of these potential disadvantages, we'd suggest offering the owner a credit in lieu of trying to obliterate the footprints.