I'm in VA with a large Trex deck (approx 1200 sq ft) that is 8+ years old. Early on I cleaned the deck several times with Corde Clean and everything was fine. Then I got lazy and several years were skipped and soon it was at least 5 yrs since it was cleaned. There were quite a few large dark stains, mold, etc because of the Virginia weather and Dogwood trees that overhang the deck. This year I got some help and a fresh supply of CC and the mixed it strong. With some scrubbing, but only one application - the deck was restored to a nearly new condition. I'm back on track to do the twice a year cleaning and keep it looking good with little effort.