Discoloration Countermeasures

If you do end up with discolored concrete, there are a number of remedies you can take to lessen the effects.

First, flush the hardened surface with hot water, followed by scrubbing with a stiff brush. This process should be repeated until discoloration disappears.

For more severe discoloration, try using a mild acid solution (1% to 3% muriatic acid) Start with a mild concentration, since muriatic acid will remove concrete as the concentration increases. Use just enough to remove the discoloration. To control the depth of acid penetration, flood the hardened surface with water first, and allow it to dry. The longer you allow the concrete to dry, the deeper the acid can penetrate. Work in manageable areas, and control the depth of acid penetration according to the drying time following flooding.

After each attempt with the mild acid, flush the area completely with clean water within 15 minutes after acid application. As when using any aggressive chemical, refer to the materials safety data sheet (MSDS) and wear appropriate clothing and eye protection.

References:

"Discoloration of Concrete, Causes and Remedies," Kosmatka, S.H., Concrete Products Magazine, April 1987.

"Effects of Substances on Concrete and Guide to Protective Treatments," Beatrix Kerkhoff, Publication IS 001.11, Portland Cement Association, 2007.

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