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Thread: cutting hole for toilet pipe

  1. #1
    DIY Member econguy's Avatar
    Join Date
    Apr 2007

    Default cutting hole for toilet pipe


    i'm doing some remodeling work, and my plumber just cut a hole for the toilet flange. right now, i only have 3/4" OSB subfloor, plus 1/2" plywood underlayment. i plan on putting down ditra and tile. the flange won't be installed until the end, right now the pipe is just a long stub-out that will be cut down.

    the hole he cut is a little too big, in that the perimeter of the flange will be supported, but the screws won't have anything to bite into.

    i have access from the basement. can i cut a patch of plywood, and screw it to the bottom of the OSB? i figured he could use some longer flange screws to screw into the patch.


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


    Yes...he should know better, though.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3


    I had a similar situation in where the top layer was cut to the size of the flange and the bottom layer a little smaller. I put expanding foam in around the pipe and trimmed it flush with the first layer. Then I put hydraulic cement in flush with the tile, then drilled that and put masonry anchors and stainless screws in to hold the flange in place.
    I consider myself an accomplished DIY'er. I don't know everything but help where I can. I'm not a pro, but like to think I'm professional.

  4. #4


    This is what happened to me, the hole was cut out too big and the toilet screws doesn't bite into anything.

    If I could go back, I would insist that part of the floor be redone until, it fits right. He fixed mine by laying 1/25 inch Louann board over it that fits nice but, the toilet leaks because the screws dangle right through the board. I can see it from the access panel. The louann board is now warping and the toilet rocks, and it leaks and leaks and leaks.

    I simply gave up.

  5. #5
    Master Plumber Dunbar Plumbing's Avatar
    Join Date
    Apr 2005
    Northern Kentucky/Greater Cincinnati Area


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