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  1. #1
    Join Date
    Jun 2012
    Posts
    81

    Default concrete subfloor- 3/4" hardwood install questions

    so I have an addition I will be putting 3/4" red oak flooring in. the subfloor is slab on grade, it has 6mil poly under the slab and was poured a year ago. I will be putting 3/4" plywood over the concrete then the hardwood on top of the plywood. I have 2 questions- 1. do I use t-g plywood or square edge leaving room for expansion? 2. what do I put on the slab prior to the plywood? I will be gluing AND nailing or screwing the plywood down. is the glue enough of a moisture barrier? the grade is below the slab and there is drain tile installed around the exterior footing.....
    thanks!

  2. #2
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,360

    Default Re: concrete subfloor- 3/4" hardwood install questions

    Depends on what is common in your area.

    ROund these parts we install 'sleepers' on the slab, usually 1x3's, perpendicular to the run of the hardwoods.

  3. #3
    Join Date
    Sep 2012
    Location
    Boston
    Posts
    821

    Default Re: concrete subfloor- 3/4" hardwood install questions

    same here, 1x3 PT sleepers with T&G plywood on top. no need to worry about expansion of the subfloor.

  4. #4
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    5,084

    Default Re: concrete subfloor- 3/4" hardwood install questions

    Slightly different over here: 6mm plastic over the slab, 3/4" plywood (reg sheets) nailed down into the slab, then the floor.

  5. #5
    Join Date
    Jun 2012
    Posts
    81

    Default Re: concrete subfloor- 3/4" hardwood install questions

    no room for sleepers- subfloor is set down 1-1/2" 3/4 for plywood and 3/4 for flooring.

    I planned on the poly but think the fasteners thru the plywood into the slab will negate the effects of the slab?

    I think a troweled adhesive with moisture resistance for the plywood?

  6. #6
    Join Date
    Sep 2012
    Location
    Boston
    Posts
    821

    Default Re: concrete subfloor- 3/4" hardwood install questions

    only if it's PT plywood

  7. #7
    Join Date
    Jun 2012
    Posts
    81

    Default Re: concrete subfloor- 3/4" hardwood install questions

    ok- I hadn't thought about PT.
    I asked local flooring guys and got all differsnt answers...............

  8. #8
    Join Date
    Jan 2008
    Posts
    1,096

    Default Re: concrete subfloor- 3/4" hardwood install questions

    Why not put treated in sleepers on close centers (like 12") then hardwood on top of them? That would allow a bit of airflow and the hardwood will do fine with the close span and nothing else under it. Lots of old houses here in the south had hardwood flooring applied directly to the joists and while not optimal, many are still in good shape 60-70 years later. And that is with 16" or more centers. Once you price the equivalent in treated plywood you'll see the merit in using sleepers! Seal the concrete, roll out the poly, install sleepers, then lay the flooring. If you wish, put rigid styrofoam between the sleepers but don't expect much insulation from it as whichever method you use, you're going to have some conduction between the concrete and the flooring through the substrate. Sleepers will lessen the contact area and thus lessen that conduction.

    Phil

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