Build up for a tiled tub surround

Discussion in 'Cork, Ceramic, Stone and Other' started by highup, Nov 13, 2018.

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  1. Nov 13, 2018 #1

    highup

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    Working on a floor, but the studs behind the tub wall have rotted. This is a 1960's style tile installation above the tub. You know, the kind where they used mastic to adhere the tile to sheetrock.
    Well, that's finally failed Layout c crop.jpg Layout c 350.jpg
     
    Last edited: Nov 13, 2018
  2. Nov 13, 2018 #2

    highup

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    2nd image shows the room. The first image is where I have my questions. It's just the red circled area enlarged.
    OK, if I get it down to bare studs, contractor mentioned it is a good idea to shim the studs a hair so tha backer board has a tny gap behind it.
    Doing that, the backer board has a slight gap behind it right at the tub flange where it's nailed to the studs. He said fill that gap with silicone before putting the backer board against it.
    He also said to leave a 1/8" gap below the backer board........ so the backer board doesn't rest directly on the tub.
    He said do the same with the tile, then caulk or grout caulk along the lower edge of the tile.
    Not done yet. :D
    I found a tile guy to come look at it tomorrow.
    He said he's put 15 lb felt on the studs, the backer board............. and I swear he said 1/4"
    dat sounds way thin to this carpet dude.

    Now, the real questions. Is any of what I described correct?
    If not, what's the correct way to seal the wall cavity and build out the wall with backer board?
    And is there any "wrong" type of backer board for tub walls?
     
  3. Nov 13, 2018 #3

    havasu

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    Any backer can and will wick up water, and this is why you keep all material off the tub top.
     
  4. Nov 13, 2018 #4

    highup

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    Doing some googling, I read on one site that you install the backer board 1/4" above the tub flange, the fill that large void with thinset when installing the first row of tile.
    If you install the board 1/4" above the flange, how does one seal the backer board from the stud in that transition area?
     
  5. Nov 13, 2018 #5

    highup

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    Tile gap.jpg Like this
     
  6. Nov 13, 2018 #6

    havasu

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    Tile and thinset will cover the void to 1/4", then color matched silicone.
     
  7. Nov 14, 2018 #7

    highup

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    But if the backer board has 15"# felt behind it, what about the gab between the backer board and the lip of the tub? That;'s why I'm wondering if the backer ought to overhang the lip of the tub.
     
    Last edited: Nov 14, 2018
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  8. Nov 14, 2018 #8

    havasu

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    I agree with you. The felt is your first line of defense for condensate drain, and if it doesn't overlap the lip, that moisture could get into your walls.
     
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  9. Nov 24, 2018 #9

    Ernesto

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    Backer rod goes under the cement board, tile goes even tighter, the fill with grout caulk to finish iff.
     
  10. Nov 24, 2018 #10

    highup

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    What holds the backer rod in place so it seals? Why wouldn't a thick bead of high quality silicon better?
     
  11. Nov 24, 2018 #11

    Nick

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    Any Photos of the Process .. Inquiring minds would like to know ..
     
  12. Nov 25, 2018 #12

    highup

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    I'm the organizer general. :rolleyes:
    I don't know how the seal was done between the tub and wall when the place was built, and I want to know how it's supposed to be done. One web site I saw said to stop the backer board at the top of the tub flange, then to pack the big gap between the tub and the backer board with thinset.
    Another guy told me the backer board may need a thin shim on the studs so the backer board slightly overhangs the tub lip............ he also said to let the backer board drop to within 1/4 inch of the tub and totally fill the void with high quality silicone.
    My part is the floor......some day. This should have been corrected 5 or 10 years ago when there was no tenant. Now the place is part torn up and there has to be some organization with the plumber and tile guy so the bathroom isn't out of commission for a week.
     
  13. Nov 25, 2018 #13

    Ernesto

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    The guy is correct about the shim, I usually never need to shim it I just support the CBU with something to there is about 1/8 in gap or so and stuff the closed cell backer rod in there, then use matching caulk to fill it. The rod keeps you from using to much expensive grout caulk. This is the best image I could find.




    Installing a Backer Rod.jpg
     
    Last edited: Nov 26, 2018
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