Shower Pan (Fiberglass) Install on Wood Floor

Discussion in 'Shower & Bathtub Forum & Blog' started by dw85745, Sep 8, 2013.

  1. dw85745

    dw85745 Member

    Oct 14, 2004
    Tucson, Arizona
    I'm getting to put a shower pan on a wood floor which is unique in my part of the country.
    The pan has cross ribbing which rest on the floor.
    In dry fitting pan the two opposite corners rest a little high (1/32) from the floor
    other than that pan looks great and level.


    1) Would it be best to use a mastic or silicon to attach the pan to the floor?
    2) Go with mortar between the cross ribbing to help support the pan?
    3) If I go with mortar, should a moisture barrier (e.g 6 mil plastic) be
    used under the pan to keep the plywood floor from degrading while the mortar

  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    SOrt of depends on how good the bracing is, but fiberglass' biggest issue is flexing and the development of spider cracks, which can lead to catastrophic failure, and starts with just looking lousy. While easy and cheap, the stuff to build an actual tiled shower pan isn't all that expensive, either, assuming you're willing to do it yourself. I think I'd try to fill those voids with mortar. You didn't say anything about level, only flat. It's critical that the pan be level, and mortar can allow you to do that, should it be needed. You don't really need to protect the floor, but you do want some moisture barrier underneath - it will help to hold the moisture into the mortar mix so that it can cure with max strength. Otherwise, the plywood floor can wick too much moisture out, which leads to weak mortar. ALso sort of depends on how deep those recesses are and if it does need to be leveled.
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  4. dw85745

    dw85745 Member

    Oct 14, 2004
    Tucson, Arizona
    The floor is both flat and level.
    The primary reason I chose the fiberglass was the weight issue -- plus -- the shower will be solid surface instead of tile.
    The underside ribbing is 6 in O.C. and the depth from the floor to the voids between the ribbing (i.e bottom of pan) is 3/4 inch.

    Great point.

    Since you recommend a moisture barrier to allow mortar to set up, this primarily answers my
    question about binding the pan to the floor which will NOT occur with a moisture barrier (e.g. sheet plastic or tile liner).
    With concrete you would get a binding between the floor and the pan.

    I plan to use 1 inch high piles about 3 inch in diameter in the center of each 6x6 recessed square, that way would get
    good support throughout the pan area with the ribbing (putting a straightedge on the bottom it appears all ribs will rest on floor)
    unless you have a better recommendation.?
    Last edited: Sep 8, 2013
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