So, I read the instructions on the website and ordered 2 bags of Corte*Clean for my 600 square foot deck. I installed the Trex 6 years ago and since it was "Maintenance Free" haven't done much more than wash it with soap and water and elbow grease. We finally got decent weather here in northern Illinois (I had a completely dry deck at least) and since it was on the cooler side, decided today was the day to try the product since it wouldn't dry to fast in the sun. I have a 4 gallon backpack sprayer, so I mixed up 4 gallons at maximum strength. As I was using the included scoop, I was surprised to barely get 10 scoops out of a bag. Glad I ordered 2, wish I had ordered 5! I applied it, brushed it, applied again, keeping the product wet on the deck for the 20 minutes. While I was waiting the 20 minutes I sprayed the next section, keeping everything wet. When the 20 minutes was up on the first section, I only had the stairs left to treat. I rinsed the first section off then treated the steps. Got to the rest of the sections on time and had just enough product left to treat the first piece a second time. What a difference! Definitely need to order more next time. I was skeptical but am now a believer!