Published on November 20th, 2012 | by Henri


White substance growing in concrete cracks

Q.      I have a growth-like substance between cracks in my concrete garage. The growth is white in color and looks like Styrofoam. I remove it, but it keeps growing back. What is it and how do I get rid of it?

A.      If the growth is very feathery and wipes off easily, it may be efflorescence – salts from the concrete being leached out by moisture that eventually dries up leaving the salts exposed. It can be brushed off and it won’t cause any harm.

However, if the growth is spongier and slimy, and keeps growing shortly after you remove it, it may be one of the slime fungi that grow very fast and breed under very moist conditions. In that case, I suggest that, wearing rubber gloves, you scrape some off with a trowel and put a sample in a glass or plastic jar. Take it or mail it to a microbiologist in the extension service of your state university after contacting him or her to be sure you are sending it to, or dropping it off at, the right place. The microbiologist will analyze the sample and recommend a treatment.

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