Posted: Thu Jun 08, 2006 11:55 am
We are trying to clean up a very old crazy paving patio - it is full of white circular stains about 2" diameter. Can anyone tell me what it is and how to get rid of it.
Probably a lichen, so you;ll need a wire brush, bleach, rubber gloves, and a good deal of patience as it can take 4 or 5 attempts to get rid of all of it. Lichens are a symbiotic relationship between an alga and a fungus. The fungus bit send hyphae, which are akin to very fine rootlets, into the stone/concrete, and the algae hang on to that for dear life.
The bleach kills the algae and upsets the fungus. The wire brush scrapes off the dead algae and the resistant fungus, but, as I said, it can take a few goes.