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I'm working on renovating a 90 year old house. It had a cast iron/ceramic tub that never had a shower, but I want to add one with a tile surround above the tub. The room is gutted right now down to the studs. I'll be applying closed cell foam insulation to the exterior wall. I want to put the tub along the exterior wall, but I'm not sure if I should put greenboard up first or just put the tub against the bare studs. I know the greenboard or cement board should come down and overlap the rim, but I'd need a double layer of wallboard (whichever) to do that. I'd also heard not to put greenboard behind cement board. Basically I'm not sure how far away from the wall I should put the tub. Should it be a half inch away or up against the studs? I'm not going to put the tub there till I notch out the joist below the tub to fit the drain tube. It won't be much of a notch. It just sits maybe an inch below the floor. Just didn't want to make the notch any wider than I have to in order to fit.
 

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I'm working on renovating a 90 year old house. It had a cast iron/ceramic tub that never had a shower, but I want to add one with a tile surround above the tub. The room is gutted right now down to the studs. I'll be applying closed cell foam insulation to the exterior wall. I want to put the tub along the exterior wall, but I'm not sure if I should put greenboard up first or just put the tub against the bare studs. I know the greenboard or cement board should come down and overlap the rim, but I'd need a double layer of wallboard (whichever) to do that. I'd also heard not to put greenboard behind cement board. Basically I'm not sure how far away from the wall I should put the tub. Should it be a half inch away or up against the studs? I'm not going to put the tub there till I notch out the joist below the tub to fit the drain tube. It won't be much of a notch. It just sits maybe an inch below the floor. Just didn't want to make the notch any wider than I have to in order to fit.
By all means wait for a more experienced person to comment, but when I put a tub in place I set it in and make sure it is level in both directions and mark the studs at the top of the flange and the remove the tub and put horizonal 2 X 4's at the level taking into account for the distance from the top edge of the flange to the under side of the tub where it will rest on the 2 X 4's. Then set the tub tight to the studded wall. I use one layer of cement board and bring it down to the top edge of the tub flange. Wall tile "usually" is big enough to bond to the wall and stick down within an 1/8th of an inch from the top surface of the tub.
 

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Naildriver
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What Mike said. Your biggest problem is the tub wasn't meant to have water splashed on the rim. It will tend to run out on your floors unless you incorporate a good sealing door system. No sheetrock needed behind the 1/2" concrete backer underlayment. Bring the underlayment down to just above the edge of the tub with 6 mil plastic behind it as shown in the illustration. Your tile will jump over the gap and the gap will prevent wicking of water when it hits the rim. Post a picture or two of your tub set up so we can see what you see.
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Okay I'll try to get some photos today. Thanks. I'll figure on putting the tub against the bare studs then unless someone has better info. does the vapor barrier go all the way up the wall or only about 6" or so just enough to seal around the top of the tub? Just wondering about condensation behind the plastic sheeting.
 

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Okay I'll try to get some photos today. Thanks. I'll figure on putting the tub against the bare studs then unless someone has better info. does the vapor barrier go all the way up the wall or only about 6" or so just enough to seal around the top of the tub? Just wondering about condensation behind the plastic sheeting.
I go to the ceiling or at least as far up as the studs are bare.
 
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Your exterior wall is foamed, so you only need 6". I would use a window flashing tape that would stick to the tub flange.
 

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Unless you are willing to waste your money on an amateur unsatisfactory job I would strongly advise a professional tiling contractor. As mentioned by another, that tub was not made for the installation you plan so you have a significant problem to overcome anyway, and if poorly done it will not only look bad, it will be subject to visible mold and hidden rot. I stopped using green board 40 years ago as well. Specify cement board and the correct, special fasteners.
 

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The tub goes against the studs. Drywall can be used (or cement board, not both). However this isn't an appropriate surface for a wet area. If tile is going to be applied, you need to cover with a waterproof membrane of some kind. I use Kerdi. Remember that cement board can't be damaged by water, but it can transmit water through to the studs. Cement board does not waterproof, and you need waterproofing.
 

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Discussion Starter #10
i was going to use something like Red Guard over either the greenboard or cement board. I was figuring on using cement board.
 

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Cement board is not waterproof so you need a membrane as chandler's picture shows, or service coating designed for such.
I'm actually not fond of cement board. I use Denshield. Denshield goes up like regular drywall and has a ceramic facing. You "tape" and seal the seams with silicone and it becomes the waterproof barrier. No membrane behind it is required (in fact, they recommend against it). The stuff is have the weight of cementboard and easier to cut and work with.
 

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Cement board is not waterproof so you need a membrane as chandler's picture shows, or service coating designed for such.
I'm actually not fond of cement board. I use Denshield. Denshield goes up like regular drywall and has a ceramic facing. You "tape" and seal the seams with silicone and it becomes the waterproof barrier. No membrane behind it is required (in fact, they recommend against it). The stuff is have the weight of cementboard and easier to cut and work with.
Where can Denshield be bought?
 

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I got it at Home Depot I think. It's a Georgia Pacific product.
Okay thanks. I did a little searching locally and found Menards carries it. Home depot had it listed but didn't stock it here.
 

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Here is a photo of the edge of the tub and where it’s going to go. I patched the floor there with 3/4” plywood but didn’t screw it down yet till i figure out where the drain will be.
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Discussion Starter #18
the closest store that sells Denshield looks like it's nearly an hour and a half away. looks like a good choice but that's pretty far to go for a few sheets of wallboard.

What's the best way to shim up the tub to make it level? It has small metal feet under it. I won't be able to reach under it once it's in place. Is that a matter of pushing it out again, shimming where the feet are, then trying it out by pushing it back in? and does just the shear weight hold it in place? I didn't notice any type of clips on the wall or even a board along the wall when I removed it. It pretty much sat along the left wall with the foot of the tub against the exterior wall. It didn't have a shower. Here is what the bathroom looked like before. Pretty horrible right? 😆
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I'm also going to have to build the wall out about 8" for the fixtures on the left since the room is that much wider than the tub is long. I figured I'd do that after I get the tub in its final location. Then the commode will go in the middle of the left wall and a larger vanity where the last one was. That will free up the corner (that has the second mirror on the wall) for a 30" wide closet. Will be a much nicer space. I'll need to move a heater grate that's in the floor on the other side of the tub fixtures in the second photo. It will just go to the left of where it currently is.
 

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I don't like relying on the feet for a tub to rest on. Use 3 or 4 thinset in dollops about as big as a cow patty under the main part of the tub. Once it is in place, stand in the tub and walk around to squish out the thinset to where it gives equal support.
 
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