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Backerboard over tub

inperfectionist | Posted in Construction Techniques on December 12, 2008 12:46pm

I’m redoing a simple three pc bath. The room, currently stripped down to the studs, if 5×12

At one end will be a 5′ tub. Backerboard will be installed above the tub, and on the backerboard, large format tile. The tile will end apprx just outside the tub area.

I would like the backerboard (I have always used concrete backerboard in the past, but may use Denshield this time) to overlap the lip at the top of the acrylic tub. To accomplish this, I was considering shimming out the studs above the tub to kick out the board 1/4″ (nom).

Thing is. I don’t want to shim out the whole room.

With the tile being 12×24, I’m thinking I could just keeep the board above the tub lip completely. and let the tile come down to the tub solo, no board. I have seen this done often, and seen it work fine, but I never felt it was the best practise.

So I’m wondering how others handle this common situation.

Many thanks, Harry

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  1. User avater
    EricPaulson | Dec 12, 2008 02:04am | #1

    It is not a good practice at all.

    I've done it many times. I can't say I know of any problems, but then I never went back to most.

    At the very least, I would fill it in with thinset, then fiber (blue) tape over that.

     

  2. CAGIV | Dec 12, 2008 02:04am | #2

    There's no reason to bring the backer board down past the lip of any tub.   All it does is make things more difficult and doesn't offer any added protection.  It actually makes matters worse if you're dumb enough to use S/R.

     

    Edit:  An exception would be a 1x1 or 2x2 mosaic

    Team Logo



    Edited 12/11/2008 6:05 pm ET by CAGIV

    1. inperfectionist | Dec 13, 2008 01:40am | #5

      Many thanks to all that replied w input.My tile are 12x24.This time around, I'm holding the board up above the lip.Harry

  3. workman67 | Dec 12, 2008 02:28am | #3

    I have done alot of baths without furring the dens-shield and just fill it with mastic but must agree that it does not make sense to stop the material 3/4" high. With large tiles it really doesn't matter but every time i do the small 2X6 bullnose tiles outside the tub i must say that i cannot stand rounding that 1 tile around the corner of the tub with like 1/2" of material to glue to. If time is not an issue, I would say fur the whole wall out. Half the time the 2X lumber is never true anyway and you tend to need to shim and sqaure anyway so why not??. I would say it would definately be stronger for when you scrub the grime off the bottom of the tiles! I have seen this done in a few older baths that i have re-done

  4. carlmccarty | Dec 12, 2008 02:29am | #4

    Why don't you just notch out the studs to recess the edge of the tub?

  5. Geoffrey | Dec 13, 2008 06:56am | #6

    Harry,

    As long as your using Denshield  you can rabbet out the back side of the backer board so the sheet can set "over" the lip, you need to be sure the face of the backer is out beyond the lip of the tub,  in other words the tub needs to be tight to the studs for this to work, you can also leave the backer about 1/8" above the lip and then caulk that seam, being sure not to allow the caulking to come out beyond the face of the backer, then install tile down to with-in 1/4" of tub deck and seal with color-matched (color-matched to grout) caulk. If using  cement BB you need to bring the vapor barrier out over the lip of the tub so water will drain into the tub and not behind it.

                      Geoff

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