Efflorescence is a crystaline deposit on surfaces of masonry, concrete.
Efflorescence on surfaces such as concrete leave a white, hazy substance behind. The cloudy material contains minerals such as salt and lime that travel to the surface of concrete by water. The water evaporates, leaving the chalky substance behind. The efflorescence requires an acidic compound to dissolve the minerals and agitation to remove it completely from the concrete
Mix white vinegar with 4 cups water in a bucket to remove older efflorescence stains. Pour 1/3 of the mixture over one 8-foot by 8-foot section of the concrete.