This is my second year using Corte Clean on my 450 sq ft. Trex Deck. I purchased my house 3 years ago which was built in 2004 with Trex deck that was part of the recalled flooring. Previous owner did not have it fixed under warranty. Every year the black mold spores come out in early spring and continue to grow as weather warms up. Corte Clean works fabulous you just need to give it time to work. I do 10' X 10' sections at a time and spray and scrub with a brush. Spray with hose to wash off. Previous owner did not maintain the deck and now after 2 years of Corte Clean deck looks amazing. Hard to believe it continues to work after it dries, but it does. Recommend this product - it's amazing and eco friendly.