I had my Trex decking and railing installed in 2002 here in northern Wisconsin which is 16 X 38 feet. I didn’t clean it for years. The railing and decking started getting black mold spots and then turning green, especially on the outer edges! You could really see the problem when the Trex was wet. 5 years ago, I purchased Corte Clean and used it. The deck looks like new and has remained looking like new. I proactively use it especially in the fall, before winter and spring and it doesn’t take near the time it initially took to get the deck clean to keep it clean. The deck stays clean and I am using much less Corte Clean to keep the deck clean. This product does a wonderful job.