Exposure to leaking water and excessive moisture can cause efflorescence stains on interior and exterior masonry surfaces. Efflorescence is a powdery white substance that forms on concrete, brick and stucco due to evaporated salt deposits within the masonry. Newly constructed structures commonly develop efflorescence from curing mortar and concrete. Although efflorescence typically does not threaten the integrity of structures, the white stains are aesthetically unattractive. Promptly clean off efflorescence from masonry surfaces.
Scrub the efflorescence with a dry wire brush to loosen the powdery white build-up. Remove as much efflorescence from the surface as possible with the wire brush.
Fill a spray bottle with undiluted white vinegar. Spray the vinegar liberally onto the efflorescence.
Scrub the vinegar-soaked efflorescence with the wire brush.
Inspect the surface for any remaining powdery white residue. If stubborn efflorescence stains persist, put on protective clothing, safety glasses and rubber gloves. Fill a plastic bucket with 1 gallon of very warm water. Slowly add ¼ cup of trisodium phosphate to the water. Thoroughly mix the solution with a paint stir stick.
Dampen a nylon bristle brush in the trisodium solution. Scrub the affected surface with the nylon brush until all efflorescence stains are completely removed.
Rinse the surface with water from a garden hose to wash away the trisodium phosphate solution. Thoroughly dry the surface with towels to remove all moisture from the masonry surface.
Spray water from the garden hose onto all nearby plants, grass and shrubs before using the trisodium phosphate solution to protect the vegetation from runoff. You can substitute a nylon sponge for the nylon bristle brush.
Keep the trisodium phosphate solution away from your eyes and exposed skin to prevent burning yourself. Follow the manufacturer's instructions on the trisodium phosphate container to prevent damaging the masonry surface.