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Foam board over waterproofing

user-413071 | Posted in Green Building Techniques on

I will have a poured concrete foundation with waterproofing applied directly to the outside off the poured wall. If I use a roll-on elastomeric material that contains solvent (e.g. Polyguard Stretch Flex), but I allow it to thoroughly dry, is it safe to then put GPS foam board on top of it, or will the dray waterproofing material still damage the foam board like it would if it was still wet? If the answer is negative, then on top of which waterproofing materials is it safe to put foam board . I am planning to put a dimple board (e.g. Arroyo) over the top of the foam board to protect the latter.

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  1. jf518 | | #1

    Did you ever get an answer on this? I am considering the same setup. Thanks

  2. matthew25 | | #2

    Once cured it should not be a problem. Only the worse VOC-filled compounds would off-gas so much and be so potent to damage foam after curing. You won’t find something like that in the course of normal construction. Make sure the adhesive for the Arroyo board is water-based (I’m pretty sure it is because it is rated for use on top of ICF walls).

  3. begreener | | #3

    I would use a Roxul based product called "Drainboard" instead of foam as it gives you 2 different characteristic that you need on the outside of a waterproofed foundation wall ...

    1. Insulation value
    2. Creates a "drainage plane"

    So that water will drain thru the fibers & then down away from the foundation wall

    I used a TUFF-N-DRI® BARRIER BOARD (which is FG) on my own foundation wall

    1. jf518 | | #4

      begreener - That is an excellent idea. I was going to use XPS with the dimple mat, but it looks I get the benefit both with drainboard.

      Stupid question: Is Roxul drainboard the same thing as Rockwool Comfortboard? It seems that Roxul rebranded as its parent company Rockwool.

      1. begreener | | #6

        Apparently yes!

    2. freyr_design | | #5

      + no ants

  4. user-413071 | | #7

    I put the Polyguard stretch flex directly onto the poured concrete, then put two layers of 2" GPS foam board over that, and finally the Arroyo drain board. If I had it to do all over again, I would stick with my first instinct, which is to build an Nexcem ICF foundation with a peal & stick waterproofing membrane followed with the dimple board. The insulation would already have been contained within the Nexcem block. It was hard to keep the top of the 4x8 sheets of foam board flat and stuck to the outside of the poured concrete wall when it was only partially backfilled. I like the Arroyo dimple board, but it is hard to apply and keep straight in a horizontal direction. We also ended up having to use a termination bar to keep the top of the dimple board tight to the wall until the backfill was completed. I didn't want to make penetration into the concrete wall, but really in the end had no other choice. See Matt Risinger videos.

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