I live in rainy Washington State where mildew and mold are constant during the Spring and Fall months. We built a Timbertech deck thinking we wouldn’t have to clean and stain it each year. We chose gray for the color to match our house. Six months later we realized that our gray deck had mildew and needed cleaning. In addition, we have a Sequoia tree near the deck that sheds bark and needles with tannin that stains the deck in the fall. I found Corte Clean on the internet and got it because it did not contain bleach. I’ve used Corte Clean for maybe ten years. Twice a year, in the Spring and Fall I clean the deck and it looks great. It even removes tannin stains on our light colored deck. I also spray plastic deck chairs that are outside all year round and they easily come clean. Corte Clean is the only cleaner I will use on my deck.