White stains or a white powdery coating on new concrete is not uncommon. Such discoloration, known as efflorescence, is caused by salts that are brought to the surface of new concrete by the natural curing process. The amount of these salts, and the resulting difficulty of removing these white stains, depends on many factors, including the amount of salt dissolved in the water used to mix the concrete, the concrete itself and the amount of salt present in the sand and gravel used in the preparation of the concrete. While the whitish discoloration in no way affects the strength or durability of the concrete, it can affect aesthetics.
Allow New Concrete to Cure Completely
Wait 60 days before attempting to remove any white stains on new concrete. This will allow the moisture in the concrete to rise to the surface and evaporate, leaving behind the salts that cause the whitish discoloration. Attempting to clean the concrete before all the salts have risen to the surface may lead to a deposit of additional white residue after the first cleaning.
Buy an Acid-Based Efflorescence Cleaner
The white residue on the surface of new concrete can be removed only with an acidic cleaner. Given enough time, acid rain can clean the majority of white concrete stains, but many homeowners do not wish to wait to remove the problem. Purchase an acidic efflorescence stain remover, available at hardware stores and home centers.
Apply an Efflorescence Concrete Cleaner
Lightly mist the concrete with water and then spray on efflorescence cleaner. Choose a moderately warm day, but if possible wait until the concrete is in the shade before spraying. Use a nylon-bristle brush to scrub the concrete once it has been sprayed with the cleaner. Wear gloves, eye protection and heavy clothing while scrubbing. Rinse off the cleaner with water after you have thoroughly scrubbed the entire area. Allow the concrete to dry.
Apply Sealer or Paint
Apply a concrete sealer or concrete paint to the clean and dry concrete after the manufacturer's specifications. The sealer or paint will help the concrete last longer and should prevent any additional white residue from rising to the surface of the concrete.