Mix water and glycerin in equal parts, then add enough clay particles to create a thick mixture.
Spread the mixture over the lichen and allow it to sit for five to 10 minutes. Then scrub it off with a hard-bristled brush.
Wash the surface with water.
Mix water and bleach in equal parts. Using gloves and a sponge, apply the mixture to the rock surface from which you removed the lichen. This will prevent lichen from growing there again.