Is PL Adhesive Safe on Pex?


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Old 07-21-17, 05:10 PM
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Is PL Adhesive Safe on Pex?

I'm doing a heated floor install and have the pex with aluminum plates built into the first layer of subfloor. The plan is for a sheet of 1/2" ply on top of that, then ditra, then tile. I'd like the 1/2" ply to be very firm so I was thinking of troweling the entire back side with PL Premium (perhaps with a 3/16" v-notch). This would bond the ply to the subfloor, aluminum plates, and the glue would also get on the top side of the pex. I like the idea but I'm not sure if the adhesive will have any adverse reaction with the pex plastic. The product says not recommended for polyethylene but I feel like that just means it won't bond well, which is fine.

Thanks!
 
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Old 07-21-17, 06:24 PM
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Boy, I sure wouldn't. The solvent's in PL adhesives are pretty strong. Might not be an immediate problem, but you don't want ANY problem for many years.
 
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Old 07-21-17, 07:37 PM
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Well is there a different adhesive that will let me do what I want? I want a continuously solid (void free) subfloor sandwich, as it should be under tile.

I love PL Premium and use tons of it. I put some all over a piece of pex earlier today and will inspect it closely. I'd reasoned that after curing the glue should be pretty much inert.
 
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Old 07-21-17, 11:19 PM
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Except you don't know how it may have chemically affected the actual makeup of the material. Maybe none, maybe a little, maybe a lot. Once you apply pressure and heat over multiple cycles, you may find that one little weak area.

If I'm picturing what you want to do correctly, why not put the PL on the 1st layer (maybe 3/8" away from the channeled area), then lay the 1/2" on top of that? It would still be just as solid wouldn't it? And less chance of contact with the PEX.

It's your house, you can do as you see fit. To me it just seems like a chance not worth taking.
 
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Old 07-22-17, 04:11 AM
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i know nothing about glue. just your question would have up all night worrying about failure some time down road. i like my sleep so i would not do it. i like gunguy idea.
 
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Old 07-22-17, 09:35 AM
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The PEX needs to be able to thermally expand in length. Will your scheme inhibit expansion?
 
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Old 07-22-17, 10:56 AM
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I've decided to do my scheme with silicone caulk. I know it's safe on the pex (multiple manufacturers advise using silicone in the channels of aluminum heat transfer plates). The silicone will fill any voids, and also help glue the pex and plates in place. It doesn't have adhesive powers anything like PL, but it's not as thick so it'll move to fill voids better, and it would be easier to tear up if someone needs to redo the floor (not me!). Yes I could do the install with PL and avoid the pex, but I want something I can get all over the plates and pex, for the reasons explained below:

I've done 'dry tests' (meaning before the pex is covered by flooring) on pex installs with aluminum plates and the plates can definitely make noise as they heat up (a dinging/popping from the aluminum flexing. I'm talking about the thinner much cheaper stamped plates, not the extruded ones. The plates need to be held still and I feel like some kind of adhesive is needed. The pex can also make noise within the aluminum channel which is why manufacturers advise putting silicone in the channel. The silicone doesn't necessarily hold the pex perfectly still but if it does move, it has to move through a permanently gummy layer of silicone, and it won't make a peep. Without the silicone if the pex moves it goes "pop pop pop pop" as there is too much static friction. I've tested this with silicone and it works great to kill sound and should also give better heat transfer to the plates.

Mike, no the pex does not need to expand in length, which is why you can bury it in concrete. Yes, my scheme probably does prohibit expansion as the pex and plates are very tight between the sleepers and the pex is 'glued' in with silicone. When the pex is heated it will expand very slightly inwards, decreasing its inner diameter.
 
 

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