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Thread: Replacing subfloor around cast iron toilet flange.....

  1. #1
    DIY Member chrisexv6's Avatar
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    Default Replacing subfloor around cast iron toilet flange.....

    Ripped up my bathroom (boy that was fun!!) and I see that I need to replace most of the subfloor, including around the existing cast iron toilet flange.

    My question is.......whats the best way to do it? The floor is above unfinished basement space. Does the subfloor itself support the cast iron pipe? If so, any ideas how to support it after I remove existing subfloor?

    I assume, for reinstallation of subflooring, I should box out around the cast iron pipe, then make a seam in the subfloor plywood so that I can slide one piece in from one side and the other from the other side, and they will meet at about the center point of the flange.....is that correct?

    Thanks in advance.

    -Chris

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    The cast is likely self-supporting, although the flange should be anchored to the subfloor. Unless you remove the flange then reinstall, you'll have to cut the subfloor so that it can be slid underneath the flange. Blocking to support the ply edges is highly desireable.

    If you are thinking of tile which would raise the total floor height, consider either removing the flange or cutting off a chunk and replacing it all with pvc so the flange can be on top of the new FINISHED floor where it is supposed to be.

    Unless that arm holding the flange is very long, it should be quite rigid. If you have any trepidation, you could install a hanger to hold it prior to cutting out the subfloor, but it normally wouldn't be needed.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Member chrisexv6's Avatar
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    Thanks for the info.

    To make it a cleaner install, could I use an inside pipe cutter to cut the cast flange off, then finish the floor (subfloor, tile, etc) then install the Oatey expander-flange thing Ive seen? I figure that would allow me to get any finished floor height (within reason) and still be able to make the flange flush with the new floor.

    Only thing I worry about with that expander thing is that it might restrict the drain flow. Installing a Toto Drake toilet, if that means anything.

    -Chris

  4. #4
    Master Plumber Redwood's Avatar
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    Yes it may interfere with the outlet horn of the toilet...
    Better than even odds!

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    All of the inside pipe cutters I've seen are for plastic pipe, not cast iron. It is very possible to remove an existing cast iron flange from the pipe. Depending on access, a good whack with a hammer will likley break it, then you can pry the lead and oakum off. If you don't have good access, then you can drill the lead out and then pry the remaining bits out. A pro could re-lead a new flange on; it might take a long throat one depending on how high the existing pipe is relative to the new floor. That would be the most durable option if you don't convert to plastic.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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