The black spots on your patio are spots of black lichen. Lichen are tiny, dust-like spores from under the leaves of plants and trees. Rain and wind then carry millions of these spores to the patio stonework. Patio cleaners, bleach, or a pressure washer can remove these black stains.But some products can damage the patio pavers, and pressure washing is a tricky task. An experienced patio cleaner will know how to handle the products and clean your patio without damaging it.