Today I cleaned a 10 year old TREX deck for the first time using CorteClean. My deck generally dries easily because most of it is in the sunshine but this summer we had unusually heavy rains and lots of cloudy days. So, for the first time, significant black mold appeared on much of the deck surface. I was afraid that it was ruined. After careful research, I decided to try CorteClean. I followed the directions and let the CorteClean do the work. I sprayed it on using a sprayer and warm water. Then I let it sit on the surface for about 10 minutes. I could see the white soap foam begin to change colors to brown as the dirt began to break down. If it looked like a deck board was drying in the sunshine, I sprayed it again. Then, I brushed lightly using a standard push broom. Throughout the cleaning I made sure to keep the surface wet. I wish I had taken before and after pictures because the results are so amazing. I'm a 60+ year old woman and - for me - this project was super easy and effective! I'd like to make one point. The instruction to start wetting the deck when the boards were in full sunshine was very important. I say that because one part of my deck never got into the sunshine and those boards didn't respond to the CorteClean like the other Trex boards. There's nothing I could do about that so I plan to do a second application there next weekend. The black mold is already gone but those boards still have some additional dirt remaining. The only hard part for me was getting all of the dirty water with soap residue off of the deck surface with the water hose. My 10-year old deck had some boards that were no longer completely level. On some individual boards there were slight dips where the connecting device pulled the TREX board down to anchor it to the support. So the rest of the board shed the dirty water while the dips allowed some of the dirty water to dry on the board. I will resolve this next weekend duirng the light cleaning by toweling dry those four to five boards with a dip. Even without that, my deck already looks incredible!