Question: There was a thunderstorm shortly after our slab was poured. The contractor covered the wet concrete with plastic sheeting to protect it from the rain. The next day there were marks from the rain and the plastic sheeting, as well as some light footprints. What can I do to resurface the affected areas and repair the concrete?
Answer: The blemishes are cosmetic and won't affect the performance of the concrete, so the slab doesn't need to be repaired to function properly. But if you do want to make repairs, you could grind the surface slightly, which likely will result in exposing some aggregate. You also could lightly sandblast the slab, removing the markings and leaving a sandpaper-like finish. After sandblasting you would see sand from the concrete mix exposed and possibly a small amount of aggregate. Today, many people would view this as creating a decorative finish.
Removing the efflorescence marks left by the plastic sheeting is more difficult. An acidic wash is one option, but would probably only remove a small portion of the markings.
Another option would be to install an overlay finish. Some are sprayable, such as those used on swimming pool decks. Or you could choose a thicker overlayment that could be finished in any number of ways, including stamping, coloring, tinting, or staining—or a combination of these techniques. Although a decorative solution may cost you a bit more, it can be a good solution.
One final option would be to use a tinted sealer. Although many types of sealers show wear patterns over time, you might look into one using a polyaspartic polyurea formulation. This relatively new material is tough and durable, it generally can be applied in a temperature range much greater than most other sealers and coatings, its application is not restricted by high humidity, and it cures very quickly.