We have first generation Trex installed 12 years or more ago. We have used many products...some with bleach. Those cleaned well but mold/mildew returned. We were willing to give Corte*Clean a try. We talked directly with Corte*Clean before using the product for additional information or tips. We feel like we followed directions to a T. We cleaned our large deck well before using Corte*Clean and we cleaned our deck at least twice with the product. The results were not perfect...but we didn't expect that. Our deck looks very good...better than we expected. We will definitely re-order with the goal of cleaning at least twice or more each year. We are VERY happy!