A few questions before I get started on my Kerdi Shower

Discussion in 'Shower & Bathtub Forum & Blog' started by sdmarkus, Nov 18, 2010.

  1. sdmarkus

    sdmarkus New Member

    Messages:
    13
    Location:
    SoCal
    Man, I love these sites...what a wealth of information I have received from all of you already-thank you!!!

    Cut out our old cast iron tub and have pretty much everything down to the studs in the bathroom. Putting in a Kerdi shower with tile surround and floor.

    Used 3/4" treated T&G ply for the subfloor. In regards to the floor, should I throw down some roofing felt before moving forward with the Hardibacker or is the treated ply sufficient? Would I run that underneath the pan area as well?

    Does one typically used Hardibacker underneath the pan or only outside of the pan area where the floor tiles will be laid?

    I'd like to insulate the walls while I have them open, one being an exterior. What's the best way to avoid the dreaded moisture sandwich?

    Thanks in advance,

    Mark
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    22,262
    Location:
    New England
    Treated wood INSIDE a house is not a good idea. It often comes from the factory almost dripping wet. Plus, when it dries out, it tends to twist and warp. If you've glued and screwed it down well, you might be okay if it has been down awhile and dried out first. Also, ensure that the ply has at least 'C' or better sides (i.e., no 'D' faces). Have you verified that the joists are strong enough for tile? A good subfloor only protects things BETWEEN the joists...the joists must be strong enough ALONG them. And, keep in mind it is not the size of the room that counts, it is the length of the unsupported span of the joists underneath, whether that extends beyond the room or not. You didn't mention if this was going to be ceramic or stone. If stone, then you need a second layer of ply, installed properly.

    You need to read the instructions on installation of HardieBacker, or any cbu...no roofing felt. You must install the cbu in a bed of fresh thinset, then screw (or nail) it down with the prescribed fastener schedule then, either as you tile or before, you need to use the special mesh tape on the seams. It's easier to do while you are tiling, then you won't end up with 'speed bumps', which can occur if you do it beforehand, then the thinset cures.

    You don't want felt or cbu under the shower pan. Over a wooden subfloor, you do want to put some metal lath in the mix if you aren't going to use the Kerdi pre-formed pan. The mudbed needs to be around an inch or more at the drain over wood, and taper up at 1/4" per foot to the longest corner. That will set the height of the mudbed all around the whole shower. You can either stack 2x4's for your curb, or use a preformed one. On the 2x4's, you'd need to install some drywall before you install the Kerdi.

    On the exterior wall, just use unfaced insulation (I assume you are planning fiberglass). The Kerdi is an effective waterproofer, and drywall on the walls is the preferred surface to apply it to.

    Check out www.johnbridge.com for help on tiling things.
  3. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    Location:
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    post(s) deleted by John Whipple
    Last edited: Mar 17, 2014
  4. sdmarkus

    sdmarkus New Member

    Messages:
    13
    Location:
    SoCal
    Thanks for the info Jim, i'll run the numbers again but pretty sure I'm good for ceramic tile.

    The subfloor is already back down and I think it's going to work out pretty well.

    I've got the Kerdi pan, finally starting to take shape:cool:
  5. "best way to avoid the dreaded moisture sandwich?" = only one membrane, any membrane. A liquid paintable membrane for example.
  6. sdmarkus

    sdmarkus New Member

    Messages:
    13
    Location:
    SoCal
    Thanks for the replies gentlemen.

    I'll run the numbers again to make sure I'm good for ceramic tile.

    The unfaced insulation should work well and I will research the kerdi/drywall combo a bit more.

    Time to get 'er done!!!
  7. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,689
    Location:
    North Vancouver, BC
    post(s) deleted by John Whipple
    Last edited: Mar 17, 2014
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