I purchased this product, based on recommendations. I had blackish spots on my light grey composite decking. I cleaned it throughly, but still had these darn spots. I searched for how to remove these spots, and saw a lot of recommendations of this product. I followed the directions for this cleaner, and could not believe the results. It’s foams up the dirt, and then you just rinse it away. Tougher spots need a little agitation with a soft brush, but that’s it. Attached you can see the cleaned boards and next to it, the spited boards I hadn’t cleaned yet. What a difference. I have already repurchased this product, in anticipation of cleaning my dock, since it is eco friendly, and plan to reclean everything in the fall. I highly recommend this product. It did exactly what everyone said it would do.