How can concrete stains be removed from automobiles that were parked too close to a wall that was being placed?
You can try a dilute solution of muriatic acid (1 part acid in 5 or 10 parts of water) on a small area to see if it works. It should help to rub simultaneously with a cloth or brush with a paint brush to help remove reaction products. There are also some proprietary materials on the market that are used to remove cement, mortar or concrete from brickwork, concrete mixers and mixer trucks. Such products can be obtained from Endico Laboratories, Box 1257, Englewood Cliffs, New Jersey 07632 or from ProSoCo Inc., Box 4040, Kansas City, Kansas 66104 and possibly others. When mortar has been in contact with some finishes for any length of time there may be a dull spot remaining after the mortar has been removed. Usually this can be rectified by the use of rubbing compound and buffing.