Deck maintenance - general question

Chapel Hill, NC(Zone 7b)

I would like to understand why I have to pressure wash a deck and what happens if I don't.

We have treated pine. It was once upon a time painted with something, but that is long gone, and the wood has acquired a gray hue. I power washed a lot of it today and yesterday, and that takes off most of the gray layer. However, there are also lots of dark green areas, which I assume are algae or molds/mildews. It is very hard to remove them - I use a bristly brush and it comes off as a greenish liquid.

Since I have done so much of it already and since I also already have some deck paint, I will finish the job at least in the exposed areas.

If I did not do any of this, what would happen?
Is there a better method (non-toxic) to remove the green stuff?
How often should one (if one should) wash and/or treat the deck?
No matter what I do, there is green stuff between the boards, will that "eat" into the wood, even if the top is painted?

Obviously, I am trying to get out of this awful job, but on the other hand, I also want to be sure that I am not loosing value if I turn lazy?

DH is much more lackadaisical than me, I want to do it right, if I have to do it.

Your ideas will be much appreciated.


Chandler, AZ(Zone 9b)

Here is a good read to help get you started:

Chapel Hill, NC(Zone 7b)

Thanks, jkochan. Made me very depressed. We have been blasting away at the raw wood with the nozzle very close, because of some of the green (and other) stuff, and I know that the wood is damaged.

Where the deck is a bit protected by overhang, there is still some stain, and it is not all that dirty there.

Here is what I am thinking:

1. use Oxiclean on green stains that are left
2. seal wood where it is raw with the sealer recommended at the site you sent me
3. stain with the (Behr) stain that we already have over both the newly sealed and the still stained parts of the deck.
4. do verticals in the spring by washing with oxiclean, then staining
5. repeat 1-4 every other year

Does that sound like a solution? I cannot see myself sanding 500+ square feet.

This deck is gigantic, runs around three sides of the house, but only about 40% is exposed, the rest is under roofing.

Thank you very much for considering my problem, I appreciate any help/ideas you can come up with.


Chandler, AZ(Zone 9b)

The link is only one of many that will pop up if you Google "deck maintenance". There is a lot of information available and you may want to do a little more reading and get other opinions. At this point, if you have damaged the wood surface with the power washing, I would suggest that you give sanding the deck some consideration. The fibers in the roughed-up wood surface will have a tendency to swell and stand up when you apply the stain/sealer, especially if it is a water based product. When it dries could be like walking on a hair brush with you bare feet. It will also take more of the stain/sealer for coverage and the look may be "blotchy" where the damage varies depending on how close the wand was where you power washed. Even though it's a large area, a random orbital floor sander would make short work of it, probably just a couple of hours. Hopefully, the damage is minimal and light surface sanding with a fine grit will knock off the rough stuff. It is a deck after all, and not a finely finished hardwood floor. On the other hand, dpending on the stain and color, not sanding may give you a distressed look and non-skid finish that you may find perfectly acceptable. You might want to do a test patch with, and without sanding, in an out of the way area to see how it's going to look/feel. An opaque stain can hide many imperfections and turn mistakes into "character". Me?, I'd rather try to correct it now, rather than later after the stain and sealer have been applied. I went through this when I lived in CA with around 1500 Sq/Ft of deck. It wasn't my favorite project and I didn't even have to deal with algae or moss. I enden up sanding down to wood and applying a clear sealer and just letting the wood turn whatever color it wanted to :-)

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