Used Corte Clean yesterday on my timbertech deck steps which were covered with black spots – I had given up hope. WOW–AMAZING, they look brand new. I am an inpatient person, so I wet (not recommended unless Corte Clean is what he wet the composite with) the steps and sprinkled the Corteclean powder on the steps, used a brush, let it set for 5 minutes, then rinsed. My steps were so bad, I had to do it 3 times on each step, but boy was it worth it. I highly recommend this product.