Algae on painted pressure treated wood

[bridgebuster]

Greetings coating experts:

I hoping I can get some help dealing with algae on painted, pressure treated lumber. I attached photos.

My deck was built in early summer 2002, late that summer I applied a stain by Cabot that was supposed to be formulated for new PT wood. The stain didn't live up to expectations. Two years ago, I decided to paint it. I power washed the wood and a week later applied an acrylic by Glidden; for a couple of months it looked good ($54/gallon it should). Last spring a lot of algae appeared on the decking, the fascia boards, railing posts, and the stair treads.

The first photo shows one of the fascia boards. The second is a typical stair tread; the last is the decking. Most likely, I'll replace the decking with Trex or similar. In addition to the algae, many of the boards are split and cracked. However, I want to keep the stair treads and the framing. The joists are in good condition. The coating on the interior joist is holding up.

Any thoughts? The deck has southern exposure and I reside in northeast Pennsylvania; about 48" of rainfall annually

Thanks

 

[Compositepro]

I suggest spraying the wood with a dilute bleach solution. You can try it on a small area to start. You should see results in a day or two.

 

[berkshire]

The chances are that when you power washed the pressure treated lumber, that you washed away the water soluble salts used to treat the timber.At least on the surface, then with your annual rainfall most of your preservative will have leached away.

Composite Pros, advice of a bleach solution will kill the Algae. Then you need a treatment of wood preservative before you re paint.
The system you use will depend on whether you are using an oil based or water based paint.
B.E.

You are judged not by what you know, but by what you can do.

 

[bridgebuster]

Thanks for the help guys. That's a good point to keep in mind - power washing away the preservative.

Now if the snow would melt.........

 

[Baileyy]

I think I also power washed my preservative away. I noticed a little algea on my roof last year, but it was no big deal. This year is much worse. Thanks for all the advice.