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I bought the Azek PVC boards from a local store and I am starting to install the boards soon. I am using pressure treated for the frame, the store I bought the board suggested to use "Joist Tape" to protect the wooden joists. But when I read further details on the production information on the Joist tape (Resisto Joist Guard). They said the membrane composed of "Elastomeric Bitumen" and they said "It is not recommended to use a product containing bitumen directly on softwood boards or flexible polyvinyl chloride".

From the joist tape product, the technology is "SBS modified bitumen", the surface that making contact with the Azek PVC is actually "High density polyethylene" not bitumen. That is confusing. The underface is "self-adhesive Silicone release film". Just wondering if it is safe to use these joist tapes? Or is there any other brand that is compatible with Azek PVC that will not void the warranty? Thanks a lot.

  • Are you using the Azek just for trim or by "deck boards" do you mean you plan to walk on them? I'm not aware of an Azek product that has structural strength. The PVC material used in their trim products gets soft in hot weather and brittle in extremely cold weather. It's great for trim, but not for supporting a load, and easily scuffs. Also, why do you need joist tape? – fixer1234 Jul 16 '18 at 22:17
  • I am using Azek PVC deck boards, they are 1" thick and designed for 16" span max (on wooden joist). It is designed to support load and you can definitely walk on them. Joist tape is for preventing the pressure treated wooden frame from being rot, that's what people suggest. Even the store I bought the board, they suggest that... but after doing some research, maybe I should opt out the joist tape. – userb00 Jul 17 '18 at 12:22
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I think you're misinterpreting that warning. The joist tape has a silicone underside and a polyethylene top side which isolate the bitumen from the wood and PVC, respectively. From the same document:

• Compatible with the majority of decking materials, such as treated wood and composite materials.

What good is the product otherwise if it can't be used on joists and decking?

  • I actually contacted Azek this morning and just got their email reply, they neither recommend or disapprove to use such product. PVC is very different from composite. I totally understand what you meant, what I am worried is that over time if polyethylene layer breaks down, bitumen get contacts with PVC board directly, it has the chemical reaction and make PVC brittle. I found a related article, not related to decking but it is very similar. Very interesting stuff... linkedin.com/pulse/… – userb00 Jul 16 '18 at 18:53
  • Then your question becomes one of risk tolerance, which doesn't fit our format very well. – isherwood Jul 16 '18 at 19:30

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