Q&A · maintenance
How do I remove biological stains like algae or mildew from outdoor stone?
Biological stains such as algae, mildew, lichens, moss, or fungi on outdoor stone can be cleaned with a diluted solution of ammonia, bleach, or hydrogen peroxide (1/2 cup per gallon of water). Apply the solution, scrub gently, and rinse thoroughly. Remember, never mix bleach and ammonia.