How to Clean Lichen From Limestone

Lichens are often misidentified as dirt stains because they are black or dark gray in color. However, lichen formations are perfectly round and are sometimes white. Lichens are a combination of a fungus and an algae, and, if left on a limestone surface, will permanently discolor limestone and cause roughness or etching. Lichens are difficult to remove, and harsh scrubbing will damage the limestone. Properly removing lichens must be done slowly.

Bucket
Water
Bleach
Stockpot
Stove
Dish soap
Long-handled spoon
Rubber gloves
Stiff-bristled brush
Garden hose
Wire brush (optional)
Gum eraser (optional)

Instructions

- 1
  Fill a bucket with a mixture of 10 parts cold water to 1 part household bleach. Pour the mixture over the entire area affected with the lichens, and extend it an additional 12 inches around the perimeter.
- 2
  Allow the bleach mixture to sit for 30 minutes to an hour to kill the lichens.
- 3
  Fill a large stockpot with water, and place it on a stove burner turned to high. Wait until the water boils, then pour 1 to 2 tbsp. of liquid dish soap into the boiling water. Stir it with a long-handled spoon.
- 4
  Carefully take the pot outside to the limestone. Pour the hot, soapy solution onto the limestone infected with lichen.
- 5
  Put on rubber gloves. Scrub the area with a stiff-bristled nylon brush, using circular motions to dislodge the lichens from the limestone surface. Continue until no more lichens come free easily.
- 6
  Rinse the limestone with a garden hose to remove the bleach and the soap residue.
- 7
  Repeat the entire process every other day until all lichens are removed from the limestone surface.

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