Corte clean did a fantastic job cleaning my deck. Although I still had a few residual stains after cleaning, they were much lighter than they had been and overall the results were better than I had ever achieved in the past 15 years of owning the deck. My primary concern was black mildew stains that were almost completely eliminated. The mildew staining under my grill mat was so improved that I got rid of the mat. Grease stains were reduced but required other cleaners to get to my satisfaction. I wouldn't give Corte clean five stars for its cleaning ability and the great customer support I received. The reason I gave the product for stars was because there are a couple matters you need to keep in mind when using Corte clean. Corte clean insists that you follow the instructions carefully. This means af fair bit of prep work and also that you apply the product during the appropriate weather conditions. In my area, which is Maryland, having the necessary warm weather without rain, so it can be a challenge. so it's a waiting igame to be able to clean the deck. Also, application of the product is not as simple as spray and wash it off. It requires care where you put it down, protecting plants around the deck, and scrubbing the deck well while it's still wet. It will take time but the results will be worth it.