Efflorescence in concrete

Out of all purely cosmetic defects of concrete probably none is as common and at the same time difficult to predict and prevent as efflorescence. The word efflorescence comes from French and means blooming or flourishing. The inspiration for this name is obvious. The crystals growing on the concrete surface can easily resemble small white blossoms. How and why efflorescence develops is explained in our MC-Pedia article.

The efflorescence process is analogous to the formation of cave stalactites. Depending on the region, the color can range from the typical white and off-white yellow to brown or even black. Although the efflorescence chemistry is rather complex, the principle behind the process can be condensed into one sentence: Diffusion-induced migration of water-soluble salts to the surface of porous material. These salts are mostly, but not exclusively, calcium and magnesium carbonates and sulfates. Alkali sulfates, carbonates, and chlorides can also be present, but less often and in smaller amounts.

Efflorescence is relatively difficult to avoid completely. Unless coated with a surface sealing protection system, practically every existing concrete surface has a layer of efflorescence on it. In most cases, this is only a visual defect and does not reduce the mechanical properties of concrete. It can usually be easily washed or brushed off.