What Causes a Concrete Basement Wall to Chalk?


Concrete is made of four ingredients: limestone, mortar, stone and clay. Concrete, along with other masonry materials, can develop unsightly white spots. These white spots or sections are a sign of high humidity, too much moisture or water leaking. This white chalk effect is called "efflorescence" and isn't harmful to the concrete or humans; it can resemble white mold but isn't mold at all. If you're unsure please contact your health department or other professional service to have it tested.


  • Efflorescence is a fuzzy white crystalline deposit on the surface of concrete. Water seeping through the concrete wall dissolves salts within the material; when the water evaporates it leaves salts or efflorescence on the surface. There are two types of efflorescence: the regular easily removed powdery type and crystallized efflorescence. When efflorescence redissolves, dries out then redissolves again it creates crystallized efflorescence.


  • Removing efflorescence is done with a wire brush or power washer and appropriate cleaner. It's important to remove it all and rinse it clean. Any remaining powder can cause the efflorescence to return. Crystallized efflorescence is harder to remove, with cleaners and acid solutions available you can remove crystallized efflorescence yourself. Make sure when working with any cleaners or acids that you take precautionary measures to ensure your safety.


  • If you're living in new construction and want to avoid efflorescence or if you want to prevent it from coming back, there are steps you can take. Make sure the basement or surrounding area is dry and draining properly away from the concrete. The most common cause of efflorescence is moisture and humidity. A dehumidifier can help keep the levels down.

Standard Sealers

  • The standard sealer will keep water from penetrating the pores of concrete; however, between the sealer and the concrete moisture can settle and cause efflorescence to repeat itself. It's maintained between the barriers but defeats the purpose of the sealer.

Penetrating Sealers

  • A penetrating sealer is more efficient, absorbing into the pores of the concrete and reacting with free lime which will form calcium silicate. The sealer fills the pores of the concrete blocking water from settling, preventing the growth of efflorescence.

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