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Thread: New shower - Wonderboard installation

  1. #1

    Default New shower - Wonderboard installation

    I just completed the PVC liner installation (no leaks) and am ready to start installing the concrete board (Wonderboard) on the walls - then pour the sloped concrete pan. I have built a recessed seat into the wall and covered this with the PVC sheeting as well. I was planning on not putting any screws through the concrete board where it overlaps the PVC which is about 10" from the floor of the shower, and also 10" from the seat.
    My question is, how to I attach the concrete board to this custom seat and the vertical sides below the seat? I was thinking of cutting the pieces fairly precise and using liquid nails to glue the corners together, but not attaching the panels with screws has me worried.
    Are screws throuh the concrete board acceptable?
    Should I tamp the sloped concrete pan in first?
    I am planning to tile the entire shower.

    I can provide pictures if that would help.

    Thanks much

  2. #2
    Plumber jimbo's Avatar
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    You must secure the cement board with screws. You do not want any flex in the tile substrate.

    You are supposed to tape all the seams with mesh tape, and mud all seams and screw heads with waterproof joint compound. This is sufficient, even though the screw penetrates the moisture barrier.

    After all, on the side of your house, the siding nails or the nails for the stucco wire lath, penetrate the vapor barrier.

  3. #3

    Default Thanks Jimbo

    This forum is amazing!

    Jim W

  4. #4

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    Should I put the concrete pan in before I do the wallboard or after?

  5. #5
    Plumber jimbo's Avatar
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    The pan needs to go first, because whatever the wall is, the waterproof barrier has to lap OVER the flange of a fiberglass pan, or over the membrane of a fabricated-in-place pan where the waterproof membrane runs up the wall about 6"

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    Whoa, lets back up here. This is not how the TCNA (Tile Council North America) says to do things.

    Since on the walls, you can't nail through it to hold it in place, you want to use the setting layer of deckmud to lock the bottom of the cbu sheets in place at the bottom.

    As to the seat, any nails you put through it will compromise it. A better solution is to put the cbu on, then use a surface waterproofing such as RedGard.

    The liner needs to be on a pre-sloped layer, then the liner, then the setting layer. You can't 'pour' the deck mud. Deck mud is a lot of sand with some portland cement in it (5:1), and is more like dealing with wet beach sand, not using cement for say a sidewalk. Two reason, it is much easier to shape, doesn't slump or flow, and (equally important) is porous to allow moisture to flow to the weep holes of the drain.

    Check out www.johnbridge.com for help on tiling.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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