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Thread: Unstable tub floor

  1. #1

    Default Unstable tub floor

    I just bought a new house and have found that, apparently, the tub was not very well installed. I smelled something strange in the closet that is on the backside of the faucets/drain and, when I opened up the access door, discovered a build-up of mold. I have pinpointed the problem to be instability of the tub, which was causing cracks in the caulking and letting water through. For the time being, I have recaulked with silicone caulk, but I would like to fix the instability.

    The tub is for a three-wall enclosure. With the little access I have, I have shimmed under the the side of the tub with no wall (i.e. between the foundation and the apron). This has given better stability to the overall structure; however, the floor of the tub is still unstable. When I step into the tub, the floor of the tub gives a little, which creates instability. From reading other posts, I understand that the installer should have put mortar under the tub to prevent this type of instability. He didn't. Given that the tub is fully installed now and I have very little access, is there anything that I can do to support the floor without completely pulling out the tub and starting over (and, ideally, without cutting a lot of sheetrock around the tub)?

  2. #2

    Default unstable tub

    You can try some foam insulation,comes in a spray can,you must fill the tub with water because the insulation expands as it dries.

  3. #3

    Default

    Do you know where I buy that stuff? What does filling the tub with water do?

  4. #4

    Default unstable tub

    Foam insulation is called "great stuff",the big box store,the stuff expands filling the tub with water will weigh the tub down,I know from experience if you do not fill the tub w/water the tub could move because of the foam insulation will expand and move the tub.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    They make at least a couple of different configurations of the foam. One remains flexible, the other is brittle. The flexible one is also low-expansion and denser. I'd go with that version. Can't say from experience...just my gut feelings.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    Plumber/Owner Norcal's Avatar
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    Default

    The mortar base isn't intended to add stability to the tub, that job is done by proper wooden framework and screws thru the flanges.

    The mortar is basically to support the bottom of a fiberglass/plastic tub from flexing and eventually cracking.

    I don't think using foam insulation is going to fix your problem...that expanding insulation is pretty weak stuff as far as structural integrity is concerned.

  7. #7

    Default

    Flex is some of the problem, so maybe it will at least help. Any other ideas?

  8. #8
    Homeowner geniescience's Avatar
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    Quote Originally Posted by Norcal
    ....that expanding insulation is pretty weak stuff as far as structural integrity is concerned...
    Can we discuss this?

    Spread out over a tub base, the weight is easy to carry. Pressing a finger into foam will not give a clear indication of what foam can do.

  9. #9
    Moderator & Master Plumber hj's Avatar
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    Default flex

    If stepping into the bottom of the tub flexs the joint where the tub meets the wall or surround, then you have more of a problem than just poor support under the floor. Filling the void under the tub may cure some of the symptoms, but the real problem, namely a poor initial installation, will remain.

  10. #10

    Default flex

    Ugh. So no way to fix other than pulling the tub out and starting over?

  11. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    Take a flat piece of foam, then take a thin piece of plywood, say 1/4". Stand on it, it will feel quite firm. The base of the tub will spread the load out, and it is point loads with foam that are a problem, not distributed loads.

    If you don't have ledger boards to support the edges, that is another problem altogether...That needs to be fixed, too. If you do take it out, you can then lay the thing in a mortar bed, and it will be nice and firm.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  12. #12

    Default

    I suspect they didnt put in the ledger boards on all the edges (e.g. on the edge where the faucets are). Is there any way to "fix" that (or at least reinforce it) without taking the tub out?

  13. #13
    In the Trades markore's Avatar
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    Old thread but anyway if you don't want to remove the tub but can pull out the shower wall on the side that's causing the problem then on some models it is possible to slip an elbow bracket down between the tub and the studs and pivot it into position such that the bottom of the tub ledge has support. The exposed part of the bracket is then screwed to the wall studs.

    You can go around and add a bracket everywhere there is a stud, but this does require removing the shower wall.

    Without removing the shower wall and/or the tub the only way to install a cleat from the backside is by cutting out enough wall finishing/framing on the backside to allow access.

    If none of these options are feasible in the short-term then removing the caulking and filling the tub so that the gap is most visible then re-caulking with a more expensive 100% silicone or marine elastomeric product specifically designed for waterproof flexible gap filling would be advised.

    Filling the tub or adding weight to the tub so that the gap is most visible before applying the sealant should improve the durability of the seal.
    Last edited by markore; 11-01-2013 at 06:48 PM.

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