TimberTech Azec fascia on deck + dark streaks
We had a TimberTech Azek deck installed last year using Landmark Gray deck boards and Landmark Brownstone fascia. Not long after the first rain, dark streaks began appearing on the fascia boards. Some streaks seem to follow from the edges of the decking, while others originate directly on the fascia itself. It’s not uniform across the deck, which makes it even more puzzling.
The manufacturer sent us a bottle of their cleaner and a brush. It did fade some of the marks, but many returned over time. They offered to send more cleaner, but we’re on hold until warmer weather. Their representative suggested the staining is runoff from the house, but we’re not fully convinced.
Have you ever come across this type of issue in your experience? I’ve attached a few pictures for reference. I’d appreciate any thoughts or advice you might have.
Replies
Hi [email protected],
I've never seen or heard of Azek Timbertech decking leach out any color; makes me think fasteners in the framing or decking could be the source. If uncoated spikes were used in the framing, you could be seeing iron oxide releasing from the heads of the nails and running down your fascia. Also, it's tough to tell from the close-up photo of your fascia (photo #2) but the fastener holes look like 16g finish nails, which are pretty small for the application, and unless they're stainless or HDG, they could be rusting as well. The stains don't really look rust colored in the photos though; is it possible that a nearby flowering tree or springtime pollen in the air is accumulating in the decking gaps and rain water is concentrating it, creating this discoloration? Hope you figure it out and good luck!
Have used Azek PVC decking since 2008 and have never seen it create it's own streaks.
What I have seen are rusting fasteners like CBJackson mentioned, brown treated lumber leaching and sticky membranes like ice and water seal leaching and running down the face of whatever is below it.
It looks to me like the stains are coming from under the deck boards and running down the fascia or start on top of the deck boards (pollen?) and wrap around to the fascia when raining.
Pop a board off or set up tests with a garden hose making sure the top is clean before you start.
Also, as CB mentioned, the finish nails are not an approved method of fastening the fascia. The board will pop off the nails, shear them off or they will work themselves out of the framing from all the movement in the board.
Thanks for the replies. The Fasteners used were 18-gauge stainless, and 9/3 exterior star drive deck screws.
All wooden deck material was pressure-treated SYP. The streaks are black and I believe appeared after the first rain in September. There is TimberTech tape used on the deck structure.
The Deck has been cleaned many times, but after every rain the streaks come back. TimberTech sent a special cleaner and brush to use.
I’ve added a close-up picture of the bench back, you can see the stains coming down the deck pieces where there is no wood behind. We had a stairway built after the deck was finished, same materials and no streaking. I’ve also added a picture of the top edges of the deck; is this normal?
I find it hard to believe no one else has had this issue, it is beyond frustrating.
Thanks for taking the time to read my post.
I searched on-line, and it seems that black streaks on TimberTech are common and due to black algae. I would guess that your problem is more prevalent on surfaces that face north or get less sunshine. TimberTech has very specific instructions for cleaning their product, and that you should not use cleaners that say they are for composite decking. I'm wondering if Wet and Forget might be helpful, as it is effective in eliminating black algae, and has a long-lasting affect on many surfaces. Be sure to test an inconspicuous section to insure that the product doesn't cause issues... Homemade solutions of baking soda and vinegar might also be helpful for your problem.
We’ve seen similar staining issues come up in facility management association https://estateagentsilford.co.uk/facilities-management-services/discussions, especially with composite and PVC fascias like TimberTech Azek. It’s often related to black algae, runoff, or even fastener reactions—especially if staining reappears after every rain. Based on your pics and others' comments, it sounds like moisture and possible contaminants (like pollen, algae, or leaching from tape or fasteners) may be the culprits.
It might help to test with a hose after thoroughly cleaning a section, as suggested, to trace the source. Also, look into treatments like Wet & Forget—just be sure to test first, as TimberTech is picky about cleaners.
You’re definitely not the only one dealing with this—hope you get a clear fix soon.
Thanks for the reply. Glad to hear I'm not the only one. TimberTech was very adamant about only using their cleaner and also sent a brush. I will try hosing after cleaning.
Is the picture of the decking edge normal? I didn't notice it until it was used for the benches. A guest actually cut her finger running it along the edge.