Published on February 5th, 2013 | by Henri0
Mildew on a Trex deck
Q. I had a deck built two summers ago out of Trex composite decking. Two summers ago, it mildewed unbelievably. It was literally black polka-dotted. I used TSP and scrubbed and scrubbed. The mildew got a lighter color but it is still there.
This past summer, I started another round of TSP and scrubbing but could not clean it up completely. The TSP also managed to make a mess of the pressure-treated wood used on part of the deck and the cedar railings. How do I clean my deck? How do I stop it from mildewing?
A. TSP will not kill mildew spores; for that you need bleach. The best procedure is to spray a mixture of equal parts water and fresh Clorox bleach using a plastic garden sprayer. Do not rinse.
TSP will remove other pollutants, or, in states where TSP is banned, TSP-PF. This will have to be rinsed off with your garden hose.
I am not sure what you mean by the TSP making a mess of the pressure-treated decking and railings. If you mean they are spotted, it may be because the TSP cleaned off dirt from the areas on which it splashed. If this is the case, treat the entire decking and railings using a mild solution such as one cup of TSP per gallon of water. You may also want to add a cup of Clorox bleach to the mix.
Be sure to cover any vegetation with plastic after drenching it as the above solutions are very harmful to it. When done, drench the vegetation again to dilute any of the solution that might have gotten on it.
Mildew spores are floating in the air all the time. You may have to repeat the process from time to time.by