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Thread: proper subfloor for a bathroom

  1. #1

    Default proper subfloor for a bathroom

    I've recently removed the tile and sbufloor in a 1967 bathroom. I am planning to replace the floor with laminate, but don't know the proper subfloor to use.

    should I use a bckerboard as a sublfoor then some type of water sealer?

    The tile floor had the concrete that appeared to be about one inch thick. Do I need to raise the floor all the way up that inch, or can I just use 1/2 inch backerboard and be happy. I realize I'll have to deal with the step up at the door, but what about the toilet flange, will I be too low in that area?

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Most laminates don't like a lot of water...is this a full bath, or half? DOes the manufacturer allow it in a full bath?

    As noted, this kindof floor needs a quite flat surface. You could use self-leveling-cement. The stuff is fairly expensive, but for a small area would allow you to get the area perfectly flat.

    Backer board (cbu) does not buy you anything unless using tile. The better thing to do is put down some plywood - it will reinforce the floor, and you can get it close to the exact height you want.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Renovator Gencon's Avatar
    Join Date
    Nov 2006
    Etobicoke, Canada


    Laminat flooring is made with an MDF backing which will absorb water and swell, making it rather unsightly.Gluing/sealing the seams will help for some time but, eventually the edges will stick up a bit.Not advisable in bathrooms unless the manufacturer recommends it.
    The 1" of concrete will probably reveal a wire mesh in it, known as a "Jersey mud job" and was done to provide a nice solid surface for the tile. this can be removed to expose the subfloor. 1/4" spruce underlayment will be fine for most flooring materials except tile. Glue it down with construction adhesive and screw it to the joists every 6" with 2" screws and in the field with 1 1/4" screws. You will need floor leveler on the seams if installing a linoleum or vinyl tile. Laminate flooring uses a foam underpad giving it its "floating" designation.This foam will hide any imperfections up to about 1/8".
    Ceramic or porcelain tile will be your best bet and would require a 1/2" CBU or an uncoupling membrane like Schluters Ditra product-good website.

    Whatever you choose, the toilet flange can be raised with either a flange extension kit or by doubling up the sleeved wax seals.


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