I've now used Corte Clean for ridding my composite deck of mold in the spring of 2013 and 2015. I skipped 2014 but regretted it because the deck was significantly more difficult to clean the next time. I'm completely satisfied with the results I achieved on both occasions. The only difficulty I experienced was associated with the mixing of the product for application via a garden sprayer. The powder simply would not dissolve completely. The first year I used paint strainers to filter the solution as it was being poured into the sprayer but that was a mess as the strainers deteriorated and became clogged beyond use in one pour. The next year I was better prepared with a wire kitchen strainer that I could use in concert with a large spoon to force the powder through the mesh, thereby mechanically aiding the dissolution of the powder. After contacting Corte Clean about this it was suggested that my water might be too hard to achieve complete dissolution but my water tested at a neutral ph of 7, or that the product wasn't "fresh." However, on both occasions the product was used within 2 weeks of its receipt. I have know way of knowing how old the product was when it was shipped to me. BTW, using hot water didn't appear to help either. If you're okay with the inconvenience of the mixing hassles, or luckier with it than me, you'll be rewarded with a clean, mold free deck.