Tub install

Discussion in 'Shower & Bathtub Forum & Blog' started by Jedi, Apr 20, 2007.

  1. Jedi

    Jedi New Member

    Mar 30, 2007
    I've bought a new air tub and it is mounted onto a large flat piece of OSB which has 3 additional strips of OSB under it at the back and 2 additional strips in the front. I've read that mounting a tub in a bed of mortar is the best. Do I just add mortar between the front strips and the back. Or should there be mortar underneath the strips as well? I'm just concerned if I squish the tub down into the bed of mortar I might loose the pitch (front to back and side to side) that these strips provide.

  2. geniescience

    geniescience Homeowner

    Nov 27, 2005
    humid summers hot, humid winters cold
    you are right. The feet are made of the same material as the base (OSB).

    When feet touch the floor, water drains out by the slope designed in the tub; that is best kept as designed. So mortar is best when around the feet and not under them. Enough to solidify that central piece of OSB, that is all.

    Without mortar the tub will still hold up too; mortar is just more support. Walk around in the tub in socks or bare feet and you may hear minute creaking or cracking sounds -- that is the beginning of little stress cracks that will be visible years in the future.

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  4. Jedi

    Jedi New Member

    Mar 30, 2007
    Would it be possible to use rigid insulation or some 2x10's instead of mortar? I'm just thinking that would be easier. But then again I guess the rubbing against the insulation might make a squeaking noise. Do you suggest placing a sheet of poly down on the sub floor before adding the mortar?
  5. leejosepho

    leejosepho DIY scratch-pad engineer

    Nov 23, 2006
    disabled-retired industrial fabricator
    200 miles south of Little Rock
    The idea is to have sufficient support under the entire bottom of the tub. The tub I installed on the concrete floor in our basement has the most solid and flattest bottom (underside) I have ever seen for a fiberglass tub, so I installed that one on top of a simple 2x4 frame made from treated lumber.

    I had planned to do the same with our new tub on the main floor, and its bottom is also very solid. But when its underside turned out to be too rough and irregular for a frame, I used stiff concrete to pack, or to grout the space between the bottom of the tub and the floor after the unit had been installed.

    However you do it, just be sure the bottom of your tub will always be "solid as a rock" for ages to come.
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