Need some contractor help on subfloors

Discussion in 'The Pub' started by samdjr74, May 14, 2015.

  1. samdjr74

    samdjr74 Supporting Member

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    Hi All,

    With the upcoming kitchen remodel I need to put down new subflooring. The previous owner butchered the sub floor so I'm going to pull up the top layer of plywood and drop in a new layer of 3/4 BC ply. My question is, is BC correct for a subfloor and should the plywood but up right against the walls or should there be some space for expansion?

    Just so you have all the details here's what I have. The kitchen had an addition put on some time in the 80's. That spurred the kitchen I currently have. The addition added a 8'x15' bump out that wasn't there before. This caused two types of subfloor, the original in the old section which is the narrow oak hardwood on top of doug fir T&G and in the new section a layer of what looks like a BC plywood.

    Then the previous owner laid out an additional layer of plywood covering both the old and new section. This was the "underlayment" for the ceramic tile. No concrete board, no membrane, just plywood then thinset. Sometimes they used wire lath in certain parts of the floor but not for the entire floor. Needless to say this didn't work too well. So now that we are going to lay down brand new ceramic tile I need a new subfloor before putting down my cement board. I'm going to rip up the top layer of plywood and drop in a new fresh layer that isn't covered in globs of thinset.
     
    Last edited: May 14, 2015
  2. DrewH

    DrewH Member

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    Oops... didn't read your question correctly. comment deleted
     
  3. samdjr74

    samdjr74 Supporting Member

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    No worries, I didn't even see what you wrote lol

     
  4. Fishyfishfish

    Fishyfishfish Member

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    Leave a gap on the walls the same as noted on the sheeting stamp (should be at least 1/8 inch all the way around. Are you using 3/4 inch t&g ply?
    Use a good flooring screw (6 inches on center around the edge/12 inches in the field) and use lots of subfloor glue. If it is post and beam construction I would insulate as well.
    Wear a respirator or goooood dust mask during demo.
     
  5. crossbones

    crossbones Member

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    Hi,
    It would take too long to give a complete instructional on a guitar site, but before you do this, go to www.schluter.com.
    The world of subflooring changed about 20 years ago, and a lot of tried and true old school methods have been proven kind of silly and ineffective.
    Some of the really bulletproof classic methods are too labor and cost intensive.
    There's a little bit of science to it, but nothing too hard.
    Of course, you're going to get the old guys saying how they have been doing it their way for 40 years, yada, yada.
    We rip their stuff up about twice a week.

    Good luck and good reading.
     
  6. samdjr74

    samdjr74 Supporting Member

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    I wasn't planning on using T&G just because the original T&G is still on the bottom, this will just sit on top of it.

     
  7. Fishyfishfish

    Fishyfishfish Member

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    Didn't catch that part. Rip up and patch what you can and thin set under durock or Hardy Board.
     
    Last edited: May 15, 2015
  8. 335guy

    335guy Member

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    Okay, as a retired flooring contractor, I'll take a swipe at this.

    If I understand you correctly, you have a layer of plywood on top of the existing subflooring, which is T&G fir boards in the original section of your home and plywood in the addition. This top layer of plywood that the previous owner thinsetted tile to is the underlayment and is covered with the old thin set.

    It will probably be best to remove the top layer of plywood underlayment, but depending on how it was put down, it might be a bear. If it was screwed down, get ready for a real workout. And hopefully, they didn't choose to use an adhesive as well, as that would tear up the 1st layer of subflooring.

    But assuming you can get the top layer of plywood underlayment up easily enough, don't assume you now must put back more plywood. Ceramic tile needs a stout substrate so as not to crack. If there is any deflection in the existing subfloor, there may not be adequate framing underneath. The joist span may be further than optimal or undersized, like using 2 x 8's instead of 2 x 10 or 12's. Another layer of 3/4"plywood will likely stiffen up a subfloor, but if you do that, then you add a layer of Hardibacker or some other tile underlayment, then the floor tile, you're going to have a finished floor height that is higher than it was before. This can cause problems with appliances, doorways, plumbing, transitions to other floors, etc.

    My point is IF the deflection of the exiting subfloor is too great, perhaps you may be able to add additional framing from below ( do you have a basement? ) to stiffen it up rather than add more plywood to the top.

    If you can go this route, then another layer of plywood may not be needed and you can simply install your tile backing board to the subfloor. When Hardibacker is installed correctly, it will also stiffen a subfloor, same as plywood will.
     
  9. samdjr74

    samdjr74 Supporting Member

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    Sort of.

    I have a layout of T&G on top of the joists in the older section of the house, then a layer of builder grade thin oak flooring then plywood which had the thinset directly on it. In the newer section I see at least two layers of plywood to match the height of the old section. The new section also had the mud down directly on the plywood.

    The older section I have full access to it from the basement but the newer section was given a fully finished sheet rock ceiling. Mind you that part of the basement is the laundry room so why they put a finished ceiling in it is beyond me.

    I can see the top layer of plywood is screwed to the lower level with sheet rock screws but I didn't even think of it being glued down, I hope it isn't.



     
  10. samdjr74

    samdjr74 Supporting Member

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    Just a crazy thought, is there anyway to break up the old concrete and leave the plywood intact?

    If the top layer of ply is glued down it might be a major pain to pull up.
     
  11. Otto Tune

    Otto Tune Member

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    I did it myself. My beams ran east west, then there was 1 x 8 wood at a 45 degree angle, then a vapor barrier, like tar paper, then I used 3/4" ply that had a T&G so the edges stayed flat. On top of that I did tile (never again, next time I'll pay someone to ruin their knees.) But, it came out great. I allowed 4 days for the job, it took 10.
    To answer your question, I allowed about 1/4" all around for expansion, same with the tile, and the 1/4 round moulding covered it up. In places where the doors crossed, I made a 1 x 4 piece of red oak with a bevel, so it covers any flaws near the door. It's stayed in place with construction adhesive.
     
  12. 335guy

    335guy Member

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    It might be glued, or partially glued, or it might not be. Hard to tell till you get into it. You could take up a small section and see.

    When you say "old concrete", do you mean the thin set covering the top layer of plywood? If so, this is what I have done it the past.

    Rent a floor drum sander and edger and use very coarse grit paper, 16 or 20 grit. And sand off the old thinset. It won't be easy going, and it will be a dusty process. You'll use a lot of sandpaper. This is probably the fastest method. There are also slow speed buffer machines that a grinding plate can be attached to, but they are a bit trickier to operate. And there's no dust extraction. At least a drum sander will vacuum up some of the dust. You could try an air chisel but that would be a very laborious task done on your knees. And you would still not have a real even surface.
     
  13. dB

    dB Member

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    lots of ways to do this...just depends on fussy you want to be about the finished product. we do higher end remodels primarily in classic old homes from the early 1900's, so dealing with many layers of flooring is part of just about every project. the two things i am particular about is making sure there is no deflection, and eliminating or minimizing any variation in finish floor height from room to room.

    if there is any tile we remove it. then we determine the thickness of the remaining flooring layers built up on the original subfloor, and set the circular to that height. so if you have 1" of layers on top of the original subfloor, we set the saw to 1" and cut a grid of 2'x2' squares. with prybars and a little leverage they usually come up fairly easily.

    for second floor projects like bathrooms, we usually do the same thing but cut all the way down to the top of the joists, and then remove all the flooring. more often than not the joists have been so hacked up from poor renovations over the years that we need to sister new joists, and it allows us to more easily run our new plumbing wherever we need.
     
  14. samdjr74

    samdjr74 Supporting Member

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    Thanks all,

    This is going to be one major PITA but it needs to get done. I appreciate the incite and hopefully it will go smooth.
     

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