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Community and Q&A

Foam Adhesive vs Tapcons for Basement Subfloor

Abindra | Posted in GBA Pro Help on


I’m in Ontario, Zone 6. I need to install a subfloor in a slab on grade walk-out basement.  And I need to minimize height.  The concrete appears dry.

Based on posts on this site I’m thinking of   concrete > 3/4″ poly faced EPS foam taped at seams > 5/8″ tongue and groove plywood > floating engineered wood floor.

I’ve seen an article elsewhere that suggests using foam adhesive to attach the foam to the concrete and to attach the plywood to the foam (instead of using tapcons).  And maybe then tapcons could be used to supplement in any problem areas.

Just wondering if anyone has tried this or just generally what you think of the idea of using foam adhesive instead of tapcons to secure the subfloor.

Also wondering if I could safely use regular (not T&G) plywood instead?

Thanks for your help.

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  1. AlexPoi | | #1

    I don't think you need adhesive for a floating floor. Personally I would float the plywood as well. No need for T&G as the plywood will be fully supported. The plywood is more of an underlayment than a subfloor in this case.

    1. Expert Member
      MALCOLM TAYLOR | | #3

      A double layer of subfloor can be floated. No single layer is suitable as an underlayment for any flooring without fasteners.

  2. Expert Member
    Dana Dorsett | | #2

    At 3/4" the foam isn't very rigid, and if it isn't secured to the floor there is almost guaranteed to have some "potato chipping" occurring with seasonal changes in moisture content of the 5/8" plywood. If the slab is clean & level foam board adhesive should be adequate. If any curls or waves appear later they can be tacked down by a TapCon or two.

    A double layer of half-inch plywood (seams staggered by a foot or more) would pretty much cure that risk, and the floor could be completely floated relative to the concrete. Using t&g wouldn't help the potato-chipping much, but would allow a bit of seasonal expansion/contraction without creating waves.

    1. Abindra | | #8

      Dana, Thanks to you and to the others for your comments.

      In using the 5/8" t&g, I'm assuming it would need to be glued to the foam board in addition to the foam being glued to the concrete. Is that right? And would using a higher density eps be of any benefit since it's only 3/4" thick?

      You mention using a few tapcons "if any curls or waves appear later".. Are you thinking of a couple of seasons down the line?

      A double layer of 1/2" plywood over foam would be ideal, but I have height limitations with the base of a couple of patio doors and some other issues in a fully finished basement.

      DCContrarian suggested below using two layers of 1/4" plywood screwed together instead of 1/2". It's an interesting idea which I never heard of. What do you think of that relative to using 5/8" t&g plywood. And if using two layers of 1/4" plywood, then no glue?

  3. Abindra | | #4

    I've also considered using fabricated subfloor panels like Dricore or Barricade because they are only an inch thick, but the consensus on this site appears to be that they are not a good solution.

  4. Expert Member
    NICK KEENAN | | #5

    I would do two 1/4" layers of plywood and screw them to each other with the joints offset. In effect making a single large piece of underlayment floating over the foam.

    1. Abindra | | #10

      Interesting idea. Never thought of that, using two 1/4" sheets of plywood, instead of 1/2".

      Only thing I'm wondering is if the lesser weight of 1/4" plywood, and lesser rigidity would make a difference. But, I like the idea.

  5. Expert Member
    Akos | | #6

    Basements flood. Always.

    Whatever you put down should allow for drainage and hold up to some water exposure. I would not put down any plywood unless tapconed down.

    I would go with one of the insulated subfloor tile products and LVT. Engineered click will also work, just be ready to replace sections of it when your water heater inevitably leaks or your washer drain overflows.

  6. gusfhb | | #7

    That seems an overstatement

    No basements don't all flood, but being the bottom of the house they can get wet

    Tapcons are strong enough to hold shelves on a wall. They are pretty tedious for holding an entire floor down

    I would suggest a vapor barrier trowel on adhesive which is what I used,

    I am also a fan of a 'T nailer' I bought for the project. Holds the material down while the glue sets.

    1. Expert Member
      Akos | | #12

      Maybe I'm in an area of older houses, but I stand by my statement.

      Leaky water heaters, overflowing washer drains, clogged house p trap, roots inside drains, broken water line on fridge icemaker, cracked toilet tanks, eroded copper fittings, burst washer lines. That is just probably the start, but at least what I have seen.

  7. Abindra | | #11

    That's an excellent link. Thank you!

  8. Abindra | | #13

    Thanks for all the replies. I'm going to glue down a layer of foam with a layer of plywood on top, probably glued to the foam.

    DCContrarian suggested using two offset layers of 1/4" plywood screwed together on top of the foam (instead of one layer of 5/8" t&g plywood). It sounds a potentially effective way of dealing with "potato chipping" and waves.

    Does anyone see any problems with this (possibly from the thinner layers of plywood) or have any other comments? I like the idea but want to make sure I'm not missing something.

    1. Expert Member
      MALCOLM TAYLOR | | #14


      If I were using two layer of something as thin as 1/4", I'd glue it together and tack it with brads until it dried. There isn't a lot of meat in two layers of 1/4" plywood to secure with screws. .

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