Extra support for Durock around tub between studs?

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Jhtx

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I'm attaching a picture here of how the tub is positioned between a couple of wall studs.

Should the Durock just "float" in this area or should I build up some 2x4 bracing a la the pink doodles? The tile edge will be the yellow stud, so if there's no support for the Durock around the pink lines it seems like it might be a tad flimsy there.

Hope that makes sense. Thanks!

Screenshot_20220324-100703_Photo Editor.jpg
 

wwhitney

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Best practice at the tub flange is to shim the studs as required for the Durock to lap down over the tub flange. That will support it at the top red line you drew.

For the vertical red line, some additional support seems wise to me. You could slip a piece of 2x blocking into the stud bay under that electrical box (or possibly flat-wise behind it) and screw through the stud from the right into the new blocking to secure the blocking.

Cheers, Wayne
 

Jhtx

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Yeah, I have read about the best practices regarding the flange and the joint where the cement board meets it and/or hangs over it. I won't be able to achieve that.

Unfortunately I can't shim the studs out because that wall extends the whole length of the bathroom. Well, I COULD, but I'm not going to - it's my mom's and she wants the rest of the drywall untouched etc. Shimming out any wall of the shower/tub basically forces me to completely gut and shim out a ton more in the bathroom due to how it's laid out.

What I thought was interesting pulling the old tile out is there was no waterproofing (original 1958 bathroom). The drywall stopped around about a foot above the tub line, and then they put a second layer of drywall over this and tiled directly on top of that. The wall with the faucet and shower head just had two tiny little 6" or so spacer squares of drywall on the studs, with again a layer of drywall attached to those and then tiled directly to that. No insulation at all anywhere.
 

Jhtx

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Normally I see blocking installed between the studs in that position. Mainly for fire blocking I believe.

tub_install_1.jpg

I've been looking at this picture for a minute and can't figure out what it's showing me for some reason. What's the highlighted deal?
 

Jeff H Young

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backing a good idea , for shower door as well. might look at towel bar backing too while your at it
 

Jhtx

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Given that I'm not bringing the Durock down over the tub flange, would it be explicitly BAD practice as far as moisture to add in horizontal support backing along the perimeter of the tub?

Part of me wants the support at the bottom of the Durock, but then that is also just wood effectively all around the entire perimeter of the tub to potentially get moisture?

I'm going to Redgard the Durock.
 

wwhitney

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How much would you need to shim? If < 1/4", you could use a 1/2" foam backer board and rabbet the bottom back to avoid shimming.

Or if you shim and don't want to change the finish plane outside the tub, you could use a quarter round tile to transition to the drywall, or an appropriate Schluter trim.

Failing all that, you could land the backerboard on top of the flange and use a strip of kerdiband or the like to marry the backer board to the tub flange/deck: a bead of kerdifx or the like to glue the kerdiband to the tub flange/deck, and normal thinset to adhere the kerdiband to the bottom of the backerboard. In which case I'd suggest just the vertical backing for the backerboard tub leg, as horizontal backerboard joints are normally unblocked anyway.

What is your waterproofing layer for the cement board?

As far as fireblocking goes, I don't think it's an issue that the stud bays communicate with each other through the underside of the tub (as long as the perimeter is under 10'), but you don't want the ceiling joist bay to communicate with the stud bays via a subfloor cutout for the tub waste. One way to fireblock, I believe, is simply to insulate the stud bays below the tub deck with rockwool batts.

Cheers, Wayne
 

Jhtx

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Shimming would likely need to be at least 1/4" in some places. I haven't measured exactly, but that's what the eye test says.

My waterproofing layer will be Redgard.

Will Kerdiband adhere to the tub flange no problem? It's a porcelain steel unit. When you say Kerdifix "or the like", what are the alternatives? I ask because I don't see that Kerdifix is in stock at my local HD or Lowe's. Will 100% silicone work similarly?

In addition to this, would it be wise to Redgard the bottom edge of the Durock that is closest to the tub flange?
 
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