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What are those powdery white areas on my concrete block wall?
Monday, January 6, 2020
The discoloration is likely “efflorescence,” which is an accumulation of minerals and salts on the surface of the block due to repeated bouts of excess water in the material. When concrete block is saturated with water, the minerals that naturally occur in the masonry material are dissolved and, as the water migrates to the surface of the brick and dissipates from evaporation, the mineral deposits are left behind as a thin layer of powder. Repeated saturation and evaporation cycles lead to a buildup of the surface powder.
When the block is sealed with paint or another sealer, but moisture has entered the wall anyway, then sometimes the efflorescence will appear along the mortar lines. See our blog post What causes raised white lines of residue on a block wall that are crusty and crumbling? to learn more about this.
While the efflorescence is only a cosmetic problem in itself, its appearance on the wall indicates an ongoing water intrusion problem, which can lead to mold growth in adjacent building materials over time. Occasionally, efflorescence is mistaken for mold. Here’s a three ways to tell the difference between the two:
1) When a sample of efflorescence is pinched between the fingers, it will crumble into a powder. Mold will not.
2) Efflorescence grows on inorganic masonry materials, while mold does not; with the exception that a dirt/dust buildup on the surface of a moist masonry wall will sometimes grow mold.
3) Efflorescence will dissolve in water, while mold will not. One common cause of minor efflorescence is a sprinkler head that sprays on the wall, like in the photo below of efflorescence on a brick wall A pressure washer and/or a diluted acid solution is typically used for removal of efflorescence, with the surface promptly dried afterwards to prevent reabsorption of the water.
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