Mark P Posted August 28, 2011 Report Share Posted August 28, 2011 I'm remodeling a bathroom. I have it gutted down to the studs and will be putting in a new tub and will tile the walls. The wall at the foot of the tub is an exterior wall and there will be fiberglass insulation with kraft paper toward the inside. The wall along the side and head of tub are interior walls. My question is what if anything should I put behind the cement board that the tiles will be placed on? Thanks Mark Quote Link to comment Share on other sites More sharing options...
David Meiland Posted August 28, 2011 Report Share Posted August 28, 2011 In my opinion, the tub walls are wet walls and should have surface applied waterproofing like RedGard OVER the cement board. If the tub has a flange it's also good to furr out the walls ~1/4" so the board doesn't have to bend out over the flange. No VB is needed behind the cement board. Quote Link to comment Share on other sites More sharing options...
kurt Posted August 28, 2011 Report Share Posted August 28, 2011 David's right, but personally, I wouldn't do any VR or waterproofing outside of the tile layer. I've never torn out a bathroom with an outside wall vapor retarder that didn't have mold or crap somewhere in the assembly. My choice is to let it breath either way. OK, I'm ready for the barrage of disagreement. Have at it. Quote Link to comment Share on other sites More sharing options...
gtblum Posted August 28, 2011 Report Share Posted August 28, 2011 I'd suggest insulating the interior walls. I used batts meant for sound proofing interior walls of commercial buildings. It does a great job of keeping shower and other noise contained to the bathroom. Quote Link to comment Share on other sites More sharing options...
Marc Posted August 28, 2011 Report Share Posted August 28, 2011 What Kurt said. I'd use 1/2" moisture resistant drywall for the furr out. Marc Quote Link to comment Share on other sites More sharing options...
Mark P Posted August 28, 2011 Author Report Share Posted August 28, 2011 Kurt - are you saying the insulation in the exterior wall (behind the cement board)should not have kraft paper? Quote Link to comment Share on other sites More sharing options...
kurt Posted August 28, 2011 Report Share Posted August 28, 2011 What's the exterior sheathing and covering? Quote Link to comment Share on other sites More sharing options...
Mark P Posted August 28, 2011 Author Report Share Posted August 28, 2011 Thanks for the input everyone! Kurt - The house was built in 1959. The covering is metal (AL). I'll have to take a look at the sheating next time I'm over there, but in this picture it looks like a manufactured wood product. Click to Enlarge 75.76 KB Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted August 28, 2011 Report Share Posted August 28, 2011 . . . My question is what if anything should I put behind the cement board that the tiles will be placed on? I don't believe that it's necessary to put anything there other than the paper that's on the insulation. There are three possible sources of moisture that can cause trouble in this wall: vapor drive, air-transported, and leaks. The amount of moisture that moves through a tiled wall via vapor drive is trivial. If you build the wall properly, there should be no air-transported moisture. If the tiled wall that you install leaks liquid water, then you'll have a big problem that the vapor barrier won't solve anyway. It might just delay your discovery of the problem. Personally, I wouldn't use RedGard on a wall like this. There's nothing wrong with the product, it's just unnecessary. Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted August 28, 2011 Report Share Posted August 28, 2011 Thanks for the input everyone! Kurt - The house was built in 1959. The covering is metal (AL). I'll have to take a look at the sheating next time I'm over there, but in this picture it looks like a manufactured wood product. Click to Enlarge 75.76 KB Looks like celotex sheathing. You know, given the age of the house, and just for fun and experience of doing it, you should consider doing mudset walls. Quote Link to comment Share on other sites More sharing options...
kurt Posted August 28, 2011 Report Share Posted August 28, 2011 Yeah, celotex. I actually like celotex. It breathes. I'd just use straight batts. If paper (easier to install), I'd slit it with a razor knife so it could breath. Mud set wall tile is a bear. I haven't done one ever since durock came out, i.e., 30+ years. Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted August 28, 2011 Report Share Posted August 28, 2011 Mud set wall tile is a bear. I haven't done one ever since durock came out, i.e., 30+ years. Me neither. And I'll never do one again. But I think it's useful to do it at least once. Quote Link to comment Share on other sites More sharing options...
SNations Posted August 30, 2011 Report Share Posted August 30, 2011 In the July 2011 Journal of Light Construction there is an article titled "An Energy Retrofit in Stages." In this project, all of the exterior sheathing was removed. Over most of the house they put up new sheathing and blew in cellulose. But at the exterior wall of the bathroom they used spray foam. If you're at all concerned (and you must be at least a little because you posted the question), I would suggest you do the same and use spray foam instead of fiberglass. Quote Link to comment Share on other sites More sharing options...
Tom Raymond Posted August 30, 2011 Report Share Posted August 30, 2011 He could get a two part kit for a couple hundred bucks and spray the whole room from inside, but it's just one room. It won't make a difference. Carefully placed kraft faced fiberglass batts are going to be far more efficient than what was originally there and won't cause any funny vapor issues. Quote Link to comment Share on other sites More sharing options...
Mark P Posted August 30, 2011 Author Report Share Posted August 30, 2011 Nice discussion and I appreciate the tips. This was a HUD foreclosure I picked up a few weeks ago. I'm going to either rent it or sell it, or rent it and then sell it. Regardless - I want to do things the correct way, I take pride in my work - even it it will be hidden behind a wall ansd no one will ever know. I'll pass on doing the "mud set wall" but thanks for the suggestion. I'll have to build character another way. Quote Link to comment Share on other sites More sharing options...
SNations Posted August 31, 2011 Report Share Posted August 31, 2011 He could get a two part kit for a couple hundred bucks and spray the whole room from inside, but it's just one room. It won't make a difference. Tom, I'm not sure what your point is. But I'm not suggesting using foam because it would improve the energy efficiency of the house. I'm suggesting its use because it's a great vapor barrier. To quote from the JLC article: "To eliminate any possibility that high indoor vapor pressure in the bathroom could drive moisture into the framing cavities, we completely filled the stud cavities of that short section of exterior wall with spray foam." Quote Link to comment Share on other sites More sharing options...
kurt Posted August 31, 2011 Report Share Posted August 31, 2011 Closed cell would work nicely for that. I've got to get in the habit of thinking foam nowadays....... Quote Link to comment Share on other sites More sharing options...
Tom Raymond Posted August 31, 2011 Report Share Posted August 31, 2011 Steve, You referenced a pretty intensive retro fit that addressed the entire envelope. Mark ripped out a bathroom. I don't know the scope of his entire project but there are economies of scale at work with spray foam. One could hire out the drywall and the fiberglass insulation for the cost of a spray foam kit, and in my market none of the foam companies will spray a job that small. There's also the pesky problem of turning a small bathroom into a styrofoam cooler while the rest of the house is left to breathe. I don't particularly like that idea. If the bath is the only room that's to be gutted, and he really wants foam insulation, then I say to put it back together without any insulation and then hit the whole house with something like Retro-Foam or Applegate R Foam. Quote Link to comment Share on other sites More sharing options...
SNations Posted August 31, 2011 Report Share Posted August 31, 2011 Steve, You referenced a pretty intensive retro fit that addressed the entire envelope. Mark ripped out a bathroom. Even though the JLC article details an intensive retrofit job, the basic principle is exactly the same as Mark's situation. I'm just taking one small idea from a larger project. I don't know the scope of his entire project but there are economies of scale at work with spray foam. One could hire out the drywall and the fiberglass insulation for the cost of a spray foam kit, and in my market none of the foam companies will spray a job that small. Agreed that economies of scale may be a problem here. This will probably need to be a do-it-yourself job. That's OK. I'm sure Mark's a handy guy. There's also the pesky problem of turning a small bathroom into a styrofoam cooler while the rest of the house is left to breathe. I don't particularly like that idea. Why? What mechanism are you proposing that might make this problematic? The author of the JLC article seems to think it's a great idea. Quote Link to comment Share on other sites More sharing options...
Tom Raymond Posted August 31, 2011 Report Share Posted August 31, 2011 There's also the pesky problem of turning a small bathroom into a styrofoam cooler while the rest of the house is left to breathe. I don't particularly like that idea. Why? What mechanism are you proposing that might make this problematic? The author of the JLC article seems to think it's a great idea. You are proposing creating an environment with a volatile RH in a confined space, and in a potential rental property no less where the standard of care is questionable. I propose a little experiment to see what would happen without an automated means of moisture control: remove the contents of your fridge, unplug it, then promptly close the door. By this time Friday, that inside of that fridge will be a furry moldy mess. It will undoubtedly take longer in the bathroom in question, but it will happen. Vapor drive and frequent periods of high RH will seek out any imperfections in the foam shell and concentrate there. If the whole building envelope is foamed there will be far more volume to stabilize the RH and lessen the effect. Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted August 31, 2011 Report Share Posted August 31, 2011 Hot off the press: http://www.greenbuildingadvisor.com/blo ... -sheathing Quote Link to comment Share on other sites More sharing options...
SNations Posted September 1, 2011 Report Share Posted September 1, 2011 You are proposing creating an environment with a volatile RH in a confined space, and in a potential rental property no less where the standard of care is questionable. I propose a little experiment to see what would happen without an automated means of moisture control: remove the contents of your fridge, unplug it, then promptly close the door. By this time Friday, that inside of that fridge will be a furry moldy mess. It will undoubtedly take longer in the bathroom in question, but it will happen. Vapor drive and frequent periods of high RH will seek out any imperfections in the foam shell and concentrate there. If the whole building envelope is foamed there will be far more volume to stabilize the RH and lessen the effect. The problem is that your experiment doesn't come anywhere close to modelling the physical situation that I'm proposing. I'm not suggesting foaming all six surfaces of the bathroom (4 walls, ceiling, floor), let alone installing a magnetically sealed airtight door. I'm just suggesting foaming the exterior wall where the vapor drive from warm and wet to cold and dry is the highest, and where cold sheathing could cause condensation and all its problems. Jim Olson, the author of the JLC article, thinks it's a good idea and I agree. Quote Link to comment Share on other sites More sharing options...
Tom Raymond Posted September 1, 2011 Report Share Posted September 1, 2011 Steve, I don't dislike spray foam, but there are limits to what can be done with two part insulation in retrofits. It is exceedingly difficult to apply it properly in confined spaces and partially gutted rooms. If it's not applied properly, you can't expect it to live up to it's performance potential. If Mark is going to gut the whole house (inside or out) spray foam is a very viable option, if not it should be limited to spot treatments for air sealing. It's prohibitively expensive and potentially problematic otherwise. Quote Link to comment Share on other sites More sharing options...
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