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Thread: Not a weekend project anymore...subfloor questions...

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  1. #1
    DIY Junior Member wwilson1's Avatar
    Join Date
    Apr 2005

    Default Not a weekend project anymore...subfloor questions...

    Ive been working on preparing a small bathroom for a tile install. The subfloor is plywood over I-beam type joists. There is a finished basement below. The joists are 16 on center and assuming they span about the width of the house they are 16ft. Generally the floor seems fairly stiff except around a floor register (3x12) right where anyone will walk entering the bathroom. I can push down on the plywood near the register and see the floor deflect (1/16"?). What should I do? I hate to add a layer of plywood as this will put the final height of the tile way above (5/8"+new layer) the carpeted hallway.

    Options Im kicking around:
    1. Suck it up and add a layer of whatever is the stiffest best subfloor based on your recommendations.
    2. Go in the basement and remove the drywall ceiling in the area below the plywood that is deflecting and try to back it up.
    3. Totally remove all (or part) of the plywood in the 60x84 floor area of the bathroom and install whatever is the best (low profile) subfloor?

    Im not under any real time constraint, and want to do whatever is best; I do have a table saw etc. but limited expertise. Any advice would be appreciated.
    Thanks, Wayne

  2. #2
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    San Diego


    1" subfloor thickness is considered minimum for tile installation. This can be achieved with 1/4" Hardibacker over the plywood. However, in you case the problem around the floor register is something else, and adding extra floor may not be enough. I would consider opening up the ceiling to see if you can box the area in with some 2X8 material.

    Between the backer board and the tile, you just have to suck up the fact that you will need to deal with issues like the flange, the doors, etc. Happens all the time.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    www.johnbridge.com is dedicated to tiling. Check it out. You need to brace the area around the register. IF your joists are sufficient for tile, then you have a couple of options - the cbu then tile, or if you want to save a little in height, a product like Ditra by www.schluter.com. Note, what you need on the subfloor depends on whether the tile is ceramic or natural stone - stone needs twice the stiffness of ceramic. John's site can also help you out to determine the suitability of your floor - check out the "deflecto" on the tool bar of the forum.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    Master Plumber master plumber mark's Avatar
    Join Date
    Feb 2005
    indianapolis indiana - land of the free, home of the brave....
    Blog Entries

    Talking tile floors

    tile floors are always a problem on wood......

    if you really want to be a man, cut out all that plywood and install new 3/4 sup floor... but this is work....

    if you only have a small area that gives , its possible jsut to install another layer of 1/4 inch plywood or 3/8 over everything .....that is gonna make it pretty stiff

    its really youir call how downand dirty you want to get.

    personally I hate tile on wood floors... they seem always to finally move and give....
    it depends on how nice you want that room, I guess...

    vinyl sheet goods seem to hold up much better over time in an area that gets lots of use.

    good luck


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