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Thread: Shower pan installation with backer board

  1. #1
    DIY Junior Member ruggles531's Avatar
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    Default Shower pan installation with backer board

    I installed a shower pan in my ensuite two years ago. The pan was a solid unit with a 1/2" lip around the edge. I installed it flush with the stud wall and put Hardiebacker 1/2" board on the wall, running it flush with the lip on the pan. This worked great and I was able to install my tiling flush between the Hardiebacker and the shower pan.

    I am now installing a shower pan in our kids bathroom. The unit I purchased for them is a fiberglass one from Maax. The instructions say to install the pan flush with the studs and to have backerboard sit flush on the lip of the pan, similar to my install above. My problem this time is that the lip is only 3/16" thick on the Maax pan. I wanted to use the 1/2" Hardiebacker again on the walls, but how do I run it flush with the pan? The only thing I can think of is firring out the wall studs for the pan area only to have the lip sit at 1/2" from the main wall stud. Below is the diagram from the Maax web site. I am planning on using Hardiebacker instead of their recommended drywall. Their diagram doesn't seem to take into account the fact that the flange/lip is only 3/16" thick

    Does that make sense? Is there a better way to do this?

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  2. #2
    ACO Shower Drain Sales johnfrwhipple's Avatar
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    post(s) deleted by John Whipple
    Last edited by johnfrwhipple; 03-17-2014 at 05:06 AM.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Test, Don't Guess! cacher_chick's Avatar
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    Much like is done with most tub installs, the bottom 1/3 of the bottom row of tiles can "hang" over the edge.
    I agree with John though, installed as drawn, the water is going right through the wall and running down behind the pan.

    Neither tile or backerboard is to be thought of as a waterproof layer.
    Last edited by cacher_chick; 04-28-2013 at 07:49 AM.

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    DIY Junior Member ruggles531's Avatar
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    In my ensuite I was told just to install the backerboard to the studs and tile right on top of it. I wasn't informed I should be putting a waterproof layer on. The Hardiebacker web site never mentioned using any. What is the recommended installation practice?

    Also, is it OK to just leave the tiles overhanging with a gap behind it in the pan, or should I shim the pan out?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    While cbu isn't affected by water, it is NOT waterproof. There are several methods that work...put a vapor barrier (typically a sheet of plastic, or some roofing felt) behind the cbu and lap it over the tiling flange of the pan so any moisture that gets back there has a path into the pan; or, apply a topical waterproofing on the surface of the cbu - this could be either a liquid membrane or a sheet membrane.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member ruggles531's Avatar
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    Good to know. I would have thought something like that would be mentioned on the Hardiebacker website. So, if I install the shower pan flush with the studs, put some poly behind the backer board and lap it into the shower pan, and leave the 1/4" gap between the backer board and shower pan lip I should be fine?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    That is one accepted practice. When tiling, it is acceptable to cantilever the tile on the wall as long as more than half is properly supported...this would not be acceptable on a floor, but then you don't walk on the wall.
    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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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    post(s) deleted by John Whipple
    Last edited by johnfrwhipple; 03-17-2014 at 05:06 AM.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

  9. #9
    Test, Don't Guess! cacher_chick's Avatar
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    The backerboard with no waterproofing will take longer to dry out between uses. Combine that with some soap scum, skin cells, etc, and you are that much more likely to have mold and/or mildew problems.
    Waterproofing the backerboard makes a lot sense, and I don't know why anyone would want to skip it.

  10. #10
    DIY Junior Member ruggles531's Avatar
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    Thanks so much for the info guys. That's some great information.

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