Lichen, algae, mold and tannins from trees that stain headstones are considered biological contaminants. Lichens roots secrete acid that will dissolve the calcium in marble and limestone. Algae, mold and lichen grow because the stone pores absorb water. Moisture in the stone during the winter months will freeze and thaw causing spalling (surface loosening of minerals and cracking).
Tannins stains are caused from leaves, nuts and bark that have fallen from trees. Headstones can be cleaned with common household ingredients that most of us have (ammonia, liquid dish soap and bleach used separately)……. Note: That this is not what natural stone restoration professionals would use, but, the cost of “not” hiring them may lead to further damage, so this home remedy will help your monument to a love one’s life, live for future generations to come.
Step #1 Soak the stone with clean water with pump sprayer, keeping stone moist for 10-20 min.
Step #6 Optional is instead of doing the restoration your self is to hire a natural stone restoration professional to clean and seal from future biological contamination and damage.