I am planning to power wash my deck and stain it afterwards. But I am confused with most of you saying Bleach it, one says NO WAY! My deck was built in 1987 as pressure treated lumber 2" thick vs. the standard 1 3/4", and was let go for the last 5 or so years by previous owners who moved out of state. It has a Cabot red stain on it; most of it gone, and a lot of green mold. It is in full sun from 10 a.m. to 4:30 p.m and it is tiered, so it slowly goes down 4 tiers. No way staining can get on french doors.

I plan on using a 2 gallon sprayer for the stain when the time comes, but pressure wash it with a Subaru Costco pressure washer. Quite a bit of wood is in bad shape. We plan on replacing in the next year or so.

  • What do the french doors have to do with your question?
    – Ecnerwal
    Commented Jul 30, 2017 at 12:53
  • The wood deck leads to the french door frame which also needs to be powered sprayed and finished to match the deck. Same kind of wood and age,
    – U-Stuff
    Commented Feb 17, 2019 at 19:26

2 Answers 2


"Green mold" on a deck is almost certainly algae, not mold.

A bleach-water mixture (not straight bleach - perhaps 1 cup per gallon at the most, considerably less might be sufficient) will kill the algae and make it much easier to remove.

I happen to know someone who (evidently) is a big fan of pressure-washers and not much of a fan of bleach or scrub brushes. They'll go 3 days with the pressure washer to do what one day with bleach and a scrub-brush would do more effectively, and the traces of algae that are left behind recolonize in short order. You can be that guy, or not...

  • not. I agree w/your take...
    – U-Stuff
    Commented Feb 17, 2019 at 19:31

I had a similar problem years ago with cedar siding and a pressure treated deck that needed to be cleaned before applying a stain. I cleaned the mildew from the wood using sodium percarbonate. With a little scrubbing it worked very well. You mix the granular powder with hot water, and since you will be working on a deck, sweep it in with a broom, hose it off with water. The residual salts from the sodium are minimal and doesn't threaten the environment.

I bought my powder at the chemicalstore.com See the link:


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