I prefer plain concrete but a lot of driveways, like ours, develop black stains. This I thought was the residue of "black mold" but I was recently told by a neighbor that minerals in the concrete may be causing the stains.
This makes some sense because the stains have discrete edges and it hard to imagine how mold would grow on sun baked concrete with discrete edges. Also, I power washed my concrete so that it was perfectly clean and in a couple of years the stains were back in the same locations. "Wet and Forget" has had no effect on them.
So, if somebody has a suggestion for preventing these black stains on unpainted concrete, I would love to hear them.
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