Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Algae on painted pressure treated wood

Algae on painted pressure treated wood

Algae on painted pressure treated wood

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


RE: Algae on painted pressure treated wood

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.

RE: Algae on painted pressure treated wood

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.

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

RE: Algae on painted pressure treated wood

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.........

RE: Algae on painted pressure treated wood

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close