You might try a mild mix of detergent and bleach and scub with a stiff broom. The mix should be fairly well diluted with water (1/2 c. bleach and
1/2 c. soap to a 2 gallons water). Rinse it well with a pressure washer or nozzle. Or go to your plant store and ask about stuff to remove moss from roofs and lawns.- posted
20 years ago