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uneven plywood subfloor

gj13 | Posted in General Discussion on August 20, 2009 07:13am

I’m in the process of installing hardwood flooring (3/4″ x 2 1/4″ prefinished maple) over 3/4″ T&G subfloor. Our plywood subfloor is uneven. The plywood around one joist in particular is up to 1/2″ high. I’ve gotten the following suggestions:

1) lay a new 3/4″ subfloor over top of the first, perpendicular to the first. IMO, the hump will simply telegraph up through.

2) pull up the subfloor around the joist, plane down the joist, and reinstall the subfloor. IMO, very hard to do because it’s T&G.

3) Sand about 1/4″ off the hump and layer 30# roofing paper to taper the difference.

4) Sand about 1/4″ off the hump and use a leveling compound to taper. Can a leveling compound be used with cleats/nails?

The builder had installed hardwood in an adjoining area–it looks like there is an underlay of 1/4″ luan plywood over the 3/4″ subfloor. Is this a possible solution to an uneven subfloor?

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Replies

  1. User avater
    Dam_inspector | Aug 20, 2009 07:22pm | #1

    Is the floor joists accessible?

    It may be possible to cut the high joist in two and sister it with another. Or saw the top of the the joist off with a reciprocating saw and sister a straight one to it.

    1. gj13 | Aug 20, 2009 07:30pm | #2

      Not accessible unless I pull up the subfloor. There is a finished basement below.

  2. cussnu2 | Aug 20, 2009 08:36pm | #3

    Why not cut out the subfloor over the section of joist you need to get at, plane the joist and then install 2x  bracing to reattach the subfloor you took out plus the piece you left in?  I've done that in a bathroom where I had rot under a toilet no need to pull up the whole piece of subfloor.

    Just pound in 2x "headers" between the joist you are working on and the ones next to it on either side.  If you cut the subfloor across the three joists, you can probably just use "headers" on the ends and sister 2x  to the two outboard joists but I didn't even do that.  I cut out between the two outboard joists and the center joist which leaves the subfloor you leave down hanging mid-air so I put in at least one additional "header" between the two on the ends (ie in the middle) and then bridged between the middle "header" and the end ones with 2x along the cut line.

    You end up with cross braces on each end supporting the cuts there and a cross brace in the middle supportting the hanging subfloor and then parallel braces between the cross braces supporting the cut parallel to the joist.  Mines under a toilet which means some pretty concentrated weight on it and it never budges.

    I would suggest you take a marker and make a line across your intended cut so you can match the piece you take out to the hole it goes in.  You be surprised how many times you can flip a patch like that before you find the right fit.

     

                                                                                

            



    Edited 8/20/2009 1:39 pm ET by cussnu2

  3. Piffin | Aug 20, 2009 08:59pm | #4

    sanding it off will be the hardest and the worst of these solutions, worst because it will weaken the subfloor and the 1/2" left will not hold the flooring nails as well.

    It would be a one hour job to simply take up the plywood and shave that one joist. saw cut opens that T&G right up, and cleats/blocking with glue will put it right back together again.

    You might need new plywood after taking it up though, if it was properly glued to begin with

     

     

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    1. FastEddie | Aug 20, 2009 09:29pm | #5

      if it was properly glued to begin with

      If it was properly glued, it would have been properly crowned."Put your creed in your deed."   Emerson

      "When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

      1. User avater
        SamT | Aug 20, 2009 09:40pm | #6

        If it was properly glued, it would have been properly crowned

        Dang it. Now I gotta clean my monitor agin.SamTA Pragmatic Classical Liberal, aka Libertarian.

        I'm always right! Except when I'm not.

      2. Piffin | Aug 20, 2009 10:40pm | #7

        Hard to imagine how somebody could've let that slip by!On second thought... 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

  4. jimAKAblue | Aug 21, 2009 02:38am | #8

    It's not unusual for one joist to hump itself out of a reasonable plane during the curing process. Yellow pine joist are notorious for this.

    I'd take up the subfloor and re-plane it.

     

  5. gj13 | Aug 23, 2009 03:24pm | #9

    Thanks for the help, guys. Yesterday I pulled up the subfloor and started planing the joists. The main culprit was about 1/2" high--the plywood sprung up when I cut it.

    Right now, everything looks good.

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