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Hardwood over slab ?

DAC747 | Posted in Construction Techniques on March 29, 2009 02:44am

I am working on a remodel [western NY] and the General wants me to install Maple 2 1/4″ X 3/4″ T&G. I have read a lot of post from a search but most of them are several years old. The house is located near a lake shore and is a slab, the houses on both sides are slightly higher in elevation so ground water tends to run to wards this house. I am thinking of either a complete plywood underlay or plywood strips glued and screwed to the concrete with a vapor barrier. The strips are probably not feasible because of the random lengths of flooring. Moisture is a concern but the General and the homeowners are set on using this Maple flooring that has already been purchased. Is applying 3/4 plywood to the slab a feasible solution and what type of glue, plywood and vapor barrier would be appropriate. Thanks for the help

             Dave

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  1. Jer | Mar 29, 2009 05:34am | #1

    Vapor barrier first (6 ml.), shoot down 1x2 (or 3)x 3/4" PT sleepers 16" oc, then 1/2" or 3/4' underlayment ply over that.
    It's a little extra labor but well worth it. While you're at it, lay down 3/4" foam board insulation between the sleepers & let them cold winds blow.

    Lake Erie or Ontario?

    1. DAC747 | Mar 29, 2009 06:00am | #2

      Sleepers and 3/4" plywood sounds reasonable. T&G plywood ? 6 mil. over the sleepers and then plywood ? Chatauqua Lake-Lakewood.  Should I shoot nails [Hilti DX 451] or should I screw it down. It's T&M so I can do the slower drill and screw. I just want to do the best I can. Thanks for the help.

                Dave

       

      1. Jer | Mar 29, 2009 02:34pm | #3

        Probably the best thing to do is to screw the sleepers down with the Tapcon screws. Yes it takes longer, but it's a better hold ultimately because the sleepers can be jolted out of place when you shoot. It takes quite a bit of time however.
        I would lay in the plastic first then put the sleepers down. I've done it the other way around and never had any problems but if you think about it, the sleepers will get wet when the moisture comes up and even if they're pt (which they should be), the constant wetness can't be good.
        If you're not screwing down your sub floor but rather nailing it down, I would use sub floor adhesive. That makes for a nice, squeak-free floor. Also, when you install your maple. use 15 lb. felt instead of red rosin paper. That will also give you more vapor barrier.I used to fish Chatauqua Lake when I was growing up in Western NY state. It's been probably 35 years since I've been there.
        Chatauqua NY has quite the history that figured soundly into the latter part of the 19th century landscape throughout America. It was where a great populist movement came about in the 1870's where people could freely gather and hear great speakers and lecturers, a "lyceum", and the arts were celebrated. I was always intrigued with the idea of Chatauqua societies that grew out of those years.
        It's good country.

  2. jimAKAblue | Mar 29, 2009 03:37pm | #4

    I would be very careful about installing anything over that slab until the moisture conditions are dealt with. Do the slab moisture tests and don't proceed any further until you are sure that the slab isn't exuding moisture. If it does, your floor will show the tell tale signs within a week or two and I wouldn't rule out buckling. You will lose your shirt if that happens because as the installer: you are the expert.

    1. User avater
      Ted W. | Mar 29, 2009 07:51pm | #6

      You will lose your shirt if that happens because as the installer: you are the expert.

      That depends on the contractual arrangement. It's the GC job to make sure things get done on schedule and in accordance with code, etc... That's why he's the General and what he get's paid for. Installation is, in itself, just the labor end of it. If a contract is written, I would include wording that places the responsibility on GC for making sure that mosture is not an issue. Something in the order of:

      "General Contractor has been advised that moisture may be an issue and orders the project to go ahead"

      or something to that effect. Otherwise, GC will probably find someone else to "get the job done", who will probably get any future jobs as well.

      ~ Ted W ~

      Tool Auctions - MyToolbox.netSee my work - TedsCarpentry.com

      Edited 3/29/2009 12:51 pm by Ted W.

    2. DAC747 | Mar 30, 2009 12:50am | #9

      The GC and I already have an agreement on the liability of this floor project. He will be liable for any moisture related problems if we proceed. I have already informed him that this is probably the worst place we could install hardwood but he has already purchased the flooring and wants to continue. I have also told him that he is free to find a different installer. I have also informed him that I will not do the installation until I [or we] can find a method that I feel confident in. The Delta system seems to be the best option so far. Anyone else ?

               Thanks Dave

      1. andy_engel | Mar 30, 2009 03:56pm | #10

        Delta with a double layer floating floor? That would provide 1 in. of nailing for the flooring, and you'd want to be sure to use shorter nails or staples so as not to penetrate the Delta.Andy

        "Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)

        "Get off your dead #### and on your dying feet." Mom

        "Everything not forbidden is compulsory." T.H. White, The Once and Future King

  3. User avater
    EricPaulson | Mar 29, 2009 04:15pm | #5

    Building science info tend to be leaning toward floating floors.

    Blue foam board over a poly vapor barrier with t&g ply on top of that. You may need two layers to nail the hardwood down and in that case you can glue and stagger the joints.

    Current wisdom seems to indicate no penetrations through vapor barrier of you just defeated it's purpose.

    You need to check closely fo water and moisture issues before planning a course of action.

    I'm not sure maple is the most stable material you can choose. Perhaps an engineered strip wood floor?

     

  4. andy_engel | Mar 29, 2009 08:59pm | #7

    Check out Bostik's website (Could be Bostick??). They have a trowel on vapor retarder, over which you can apply their urethane adhesive to glue down a plywood subfloor. Or, you could just use the vapor retarder and nail the flooring to a floating floor comprised of a double layer of 1/2 in. plywood. Both methods satisfy the WFMA.

    Do check the moisture over the full thickness of the slab, and do make it so the GC owns the liability.

    Andy

    "Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)

    "Get off your dead #### and on your dying feet." Mom

    "Everything not forbidden is compulsory." T.H. White, The Once and Future King

  5. ted | Mar 29, 2009 11:35pm | #8

    First, skip the furring strips and underlayment. Even with ridged insulation the floor will be cold in winter. Second, if they have kids or a dog the engineered floating wood laminate floors are inferior IMHO to solid hardwood.
    I've used Delta FL on a couple of jobs now and it beats the heck out of the old method of furring strips, Vapor barrier, insulation and sheathing in terms of labor and finished product.

    http://www.deltafl.com/

    The floor actually feels a lot warmer and the air space created by the dimples keeps the floor nice and dry.

    1. DAC747 | Apr 01, 2009 04:08am | #11

      Ordered the Delta FL. They recommend screwing with tap cons every 24". That doesn't sound like enough to me, I am thinking every 16". Thanks again to all that poted. Dave

      1. ted | Apr 01, 2009 04:20pm | #12

        when i put it down i used 3/4" T&G and glued at the joints over the Delta FL. Screwed every 24" as they suggested. Haven't had a problem yet.

        Edited 4/1/2009 9:21 am ET by ted

      2. [email protected] | Apr 01, 2009 09:48pm | #13

        The 24" spacing should be adequate.  You are basically pinning it into place so it can't slide. 

        1. silvertip | Apr 02, 2009 04:11am | #14

          I built a custom home a few years ago.  We strapped the with 1x4 at 16" O/C and put 3/4" rigid insulation between them.  Then we sheeted the floor with 3/4" t&g plywood.  It was the only way the installer of the hardwood would warranty the floor install.

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