My composite deck had not ben cleaned with a chemical cleaner since it was installed more than five years ago. I had used soap and water to remove the pollen over the years, but the mold was virtually unbeatable. I used Corteclean as directed and in one application the results were excellent. The mold has disappeared from 95% of the decking. I have a couple small areas that I will clean again and expect that all evidence of the mold will be removed. When I cleaned the deck, half of the deck space was in bright sunlight and half in the shade. It appears that the cleaner was most effective where direct sunlight was reaching the deck.