Cement board under shower and tub?

Discussion in 'Shower & Bathtub Forum & Blog' started by ehlinn, Jan 26, 2005.

  1. ehlinn

    ehlinn New Member

    Messages:
    26
    Location:
    Maryland
    I am getting ready to start rebuilding my gutted bathroom. Is it a good idea to cover the entire floor with cement backer board, and install the tub and shower on top of that rather than just installing them on the plywood subfloor? I noticed my old shower and tub were placed right on the plywood subfloor and the tile underlayment and tile were butted up to the sides of the shower and tub.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,153
    Location:
    New England
    The only thing you might want to put on the floor under the tub is some deck mud to support the bottom (assuming it is not cast iron). My unprofessional opinion.
  3. ehlinn

    ehlinn New Member

    Messages:
    26
    Location:
    Maryland
    Thanks. It is a fiberglass tub, and I am definitely going to put some deck mud under it.
  4. Squints2See

    Squints2See New Member

    Messages:
    33
    Location:
    West by God Virginia
    is deck mud slang for concrete?...........or is this something else :confused:

    I'd like to know because I gotta do the same thing, install a new one piece fiberglass tub and the bottom of the tub sits about 4 inches off the floor......Do you have to have support under the fiberglass tub, or is this an "optional" thing?

    Thanks,
    Todd
  5. ehlinn

    ehlinn New Member

    Messages:
    26
    Location:
    Maryland
    A lot of guys use sand mix, which you can buy already mixed or mix yourself. It is portland cement and sand.

    http://www.quikrete.com/catalog/SandMix.html

    It is highly recommended to set a fiberglass or acrylic tub or shower in a bed of topping mix to prevent sqeaks and future cracking of the tub or shower floor. It also makes the tub or shower feel much more solid.

    I still want to know if anyone covers their entire floor with cement board before installing fixtures. Seems like it would be good to have under the tub and shower. Of course I will still be using the topping mix.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,835
    Location:
    Cave Creek, Arizona
    board

    There is no reason not to do it, but also no overpowering reason to do it, since the water is not going to leak through the tub or shower base.
  7. RioHyde

    RioHyde Plumber

    Messages:
    339
    Location:
    Cincinnati, Ohio
    I dont put cement backerboard under tubs. I use sandmix, set it in place, anchor it, pipe it up. For asthetic reasons I like to have the backerboard as well as the tile come up against the skirt of the tub. I guess its really a personal preference. As was said by HJ, no real reason to do it nor any overpowering reason to do it. A few dollars more involved to put it under the tub I guess.
  8. ehlinn

    ehlinn New Member

    Messages:
    26
    Location:
    Maryland
    thanks

    Thanks for the tips guys.
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