In 2009 we built our deck using timber tech twin face composite. we were aware that all composites had mold issues. We had ideal conditions with full sun ,no trees, didn’t cook on it , and had proper pitch for water runoff. Cleaned it every spring and fall with ordinary household products and for about 4 years had no real issues, then the black dots started. Tried to power wash it along with several deck cleaners but none would do the job. Around year 7 it was getting really bad especially when it rained. Came across corte clean and gave them a call. Tech support was great and had all my questions answered.Ordered one bag just to test it out. I had a few problems but was able to correct them. The first was your supposed to keep the corte clean from drying for a min. of 20 minutes,but I had a hard time because i sprayed it on in the middle of the day in full sun. Corrected that by applying it the next time in the late afternoon. The next was the sprayer i bought sprayed in a fine mist and it took too long to wet the deck. Corrected that by drilling the nozzle hole larger. Other than that the product worked great. we were afraid it would bleach the deck but it didn’t.There was a little color change where the black was but we’re sure it will even out from the sun. To us it doesn’t even matter because the deck looks way better without the black mold. Our timber tech deck is now 8 years old and looks great again. We are totally satisfied with the product. It did what it was supposed to and we would recommend it to a friend.