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Thread: Which is the real tub bottom?

  1. #1
    DIY Senior Member miamicanes's Avatar
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    Default Which is the real tub bottom?

    I'm looking at the installation guide for my new bathtub (Laurel Mountain Whirlpools 42x72 acrylic soaking tub from Lowe's), and trying to figure out which part of the tub is supposed to sit on the actual floor.

    Beneath the tub's acrylic bottom is an OSB panel. That panel is sitting on two hollow fiberglass shells. The manual seems to imply that the shells sit on the floor, but I'm not entirely convinced they aren't just for shipping, and the OSB is what's intended to sit on the floor. The fiberglass shells just don't look terribly strong.

    Here's the relevant paragraph from the manual:

    Floors of bathtubs are reinforced in the factory by installing a wood subfloor and a molded fiberglass base. Bases are designed to give uniform support to the tub floor.
    That seems to suggest that the inverted bowl-like fiberglass shells are supposed to stay and serve as the tub's ultimate foundation... but I could definitely use some reassurances, or at least some other opinions about whether the shells are clearly the base, or whether it needs more investigation.

    I'm attaching a pic of the front of the manual (I can't get a good pic of the actual tub, because it's sitting in the bathroom along with the old tub right now, and there's barely room to walk in there, let alone get a good vantage point for a photo)
    Attached Images Attached Images  

  2. #2

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    Leave the molded shells on and set the tub in mortar to support and level it. Sometimes we have to trim the shell around the pump a bit to fit the tub inside the deck.

  3. #3
    DIY Senior Member miamicanes's Avatar
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    ^^^ Question: I already made a level surface with self-leveling concrete. However, I suspect setting the tub in a bed of wet mortar will help anchor and secure it, even if it's not strictly needed for leveling. How thick of a layer should I lay to ensure that there's enough to keep the tub anchored in one spot, but not so much that it prevents the edges of the fiberglass supports from displacing the wet mortar and resting directly on the already-level bed?

    Likewise, after the tub has been placed & the drain is connected, should I grab a trowel and put more mortar along the outside surface of the bottom fiberglass supports (at least, along the sides I can get at) to help anchor it a little more? Or is something like a half inch or so of mortar on both sides of the bottom support shell surface more than enough to keep the tub firmly in place?

    What's the slowest-curing mortar you can buy somewhere like Home Depot or Lowe's? One thing that worries me (well, one more thing) is the possibility of setting the tub down in wet mortar, then discovering that there's a problem with the drain that requires another trip to Home Depot/Lowe's & more time-consuming work while the mortar is already starting to cure.

    Also, is there any good way to test the new drain to discover any leakage problems before it's "too late" (ie, stuff has dried/cured/hardened, or otherwise gotten into a state whereby it's basically going to have to be torn out and replaced entirely)? Or do drains tend to be minimal problems if they're done carefully, since they're not subjected to constant water pressure, and in almost every case the path of least resistance (where the water will want to go) is through the pipe, not through a joint?

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    The mortar is for support, not to anchor it. It is generally used to ensure the tub sits level and at the desired level. A major secondary benefit (and it may not provide that on yours the way the bottom is designed) is to provide support for the bottom. This makes the tub feel much more substantial (as if it was made of cast iron). this can help prevent stress cracks over time.

    You can use something like a sand mix...this is a mix of mostly sand with some portland cement in it. It's more like wet beach sand than cement or mortar you'd use to set bricks or tile.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default tub

    Put plastic over the mortar/mud to keep the tub from sticking to it. Seeing that picture reinforces the reply about the skirt. That tub is NOT intended to have a skirt.

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