Our composite deck was badly stained from years of neglect. The deck was stained with barbeque grease, mildew, planter rings, and organic material (leaves, bird droppings, etc.). We tried cleaning with a mild detergent which did nothing. We tried a power washer which started to damage the material. I bought Corte-Clean as a last hope of restoring our deck. Used as directed, it delivered as promised. I could not believe the difference! Even the barbeque grease stains were significantly improved. Corte-Clean does not promise to remove every stain, but it was definitely worth the money. I will continue to use this product and just purchased it for the second time to treated the rest of the deck.