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I am looking for suggestions on cleaning my composite deck.....there is some green mold and mildew.
powerwasher should do the trick nicely
Power washing a newer deck should be no problem, but for older decks power washing may be too strong, so use a chemical cleaner instead. Bleach or corte-clean are two examples. An older deck will actually lose it's top layer in power washing.
I had this problem power washing my deck that was quite old and actually made a mess of it. I'd go with the chemical cleanser option to avoid damage.
Would bleach discolor the deck?
I've used bleach on roofs and decks and never noticed color changes. But YMMV.
I would second that caution on older decks. The older Trex decks will erode under a strong pressure wash and leave you looking at the sawdust filler that is in the plastic!
Behr's Deck Cleaner, a mild oxalic acid and enzyme solution, can be used to clean decks and other household surfaces. Zinsser's "Jomax" is also good on almost any surface. It is mixed with clorine bleach, but at a lower concentration than most cleaning solutions. I've used Jomax for about 40 years and have never had a problem with it.
If algae and mildew are your main concerns, I would go with the Jomax, however, if you know the manufacturer, it might be a good idea to check with them first. Also a good idea to test a small spot before committing to flooding the whole deck with the solution.
I used Corte Clean on my composite deck. Very pleased with the results. Deck was neglected for years by the prior owners, and except for a few deep stains, it looked like new.