Efflorescence, meaning “to flower out” in French, is the migration of salt to the surface of a porous material (like slate, marble & limestone) where it forms a crust or coating.

Efflorescence is a common occurrence especially in outdoor areas or in areas where there is a lot of water such as a sunroom with an indoor hot tub. Efflorescence is caused when soluble salts move to the surface of tiles, usually as a result of water below the flooring. It appears as a whitish film or powder and is hard to remove. Usually the best strategy is to start off with a gentle method.

  • Scrub with a stiff brush and mild detergent or plain water. Efflorescence is most soluble when it first appears, so sooner if you catch it early you should have better success. When efflorescence is wet it can seem to disappear but it reality it becomes transparent so you are going to need to use some elbow grease to remove it entirely.
  • Always be sure to rinse thoroughly. If you leave dissolved salts on the surface, they’ll return as new efflorescence.
  • Pressure washing also can be effective in removing surface deposits. Keep the pressure as low as you can to do the job. A spray that’s too intense may actually open pores in concrete or brick and encourage further efflorescence.

The most important thing however is to make sure that the source of the water is minimized to prevent further damage. If it is outdoors make sure sprinklers etc are faced away from the stone and inside make sure that water is not allowed to dwell on the surface of the floor.