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Subfloor vapor barrier

deerefan | Posted in Energy, Heating & Insulation on June 19, 2022 11:22am

Good morning,

I am looking for advice on what vapor barrier to use under a subfloor. My house has a slab on grade foundation. In half, I will be putting hardwood floors from fallen pecan trees on our property. I plan on using 3/4″ advantech subfloor. I considered using Delta Fl, however, it would increase the height of my floor excessively, messing with transitions. The other option would be DMX, but I am a little concerned about how well this material seals around penetrations due to fasteners anchoring the Advantech to the concrete. I read some about Tremco Vulkem 350, which is a roll on product that would seem to seal around fasteners. Henry tech support recommended using Moistop 15, which is really for underslab use.  Now, I have no idea on what would be best. Any advice from experts on this forum would be greatly recommended. Thank you.

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Replies

  1. Greg_E | Jun 20, 2022 08:53am | #1

    Is this a new build? What was done for underslab moisture mitigation? If it is a remodel have you had moisture issues in the slab?

    1. deerefan | Jun 21, 2022 07:39am | #2

      It is a new build, I put Stego wrap under the slab, painstakingly sealing all the penetrations. The slab has been exposed for over a year now and I have not seen any obvious moisture issues. I am really interested in something that would seal around the fasteners. Thank you for your help.

  2. Greg_E | Jun 21, 2022 11:55am | #3

    I wouldn't use anything that will trap moisture in the slab. With the stego underneath you won't have moisture issues. Put a layer of tarpaper down under the advantech or paint the floor with drylock. All you need is something with lower permeability than the floor.

  3. florida | Jun 22, 2022 04:46pm | #4

    I can't imagine a worse wood for your purposes. Pecan warps and twists just from teardrops and you'll have lots before you get those trees down and dried and milled into flooring. Any moisture and that pecan will tie itself into knots.

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