Vapor barrier behind cement board and how to attach to existing iron tub...

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winneymj

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Hi,
I am remodeling my bathroom and had to remove the old cement board around the 3 sides of the tub when removing the old tile.
The tub is the original 1920's iron tub and I am going to get it refinished in-place.
My question is re-installing the cement board on the exterior wall and how to terminate the vapor barrier at the top of the tub.
I cannot get the vapor barrier past the top of the tub and to the floor as I do not have access.
What is the best way to terminate the vapor barrier at the tub?
Attached is a picture of the back of the tub (before I replace the old insulation stud shims)
PXL_20220808_203636516.MP.jpg
 
Suggestion before you cover up the walls: take careful measurements of stud locations. Add more if needed so that you can accommodate a safety bar screwed into studs.
 

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Twowaxhack said:
When I do a shower, I place solid 2x12 blocking from about 28” - 39” high all the way around the shower perimeter.
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You are in a minority, One of the few who do it right… builders surely don’t think about it and most people don’t care until they need to install a safety bar.
Almost as dangerous as no safety bar is one installed with molys and not into studs.👍👍👍

In my case above, my house was completed before I moved in as a builders spec. As it was identical to my neighbors house under construction except for the elevation, I was able to photograph every room, every wall, every ceiling and basically everything in the house before the walls went up. It made installation of the safety bar considerably easier. Yes I have a good stud finder but it always helps to know what you’re looking for, and a photograph of my tub area allowed me to map everything out and buy the appropriate sized safety bar.
 
The good old "is a moisture barrier behind cement board required" debate. Here's a few views.

1. Yes, but it depends on the area in which you live. It may be advisable to use one if your house is located in an area with high humidity or dampness to prevent mold and mildew from growing inside your wall cavity.

2. I would never use plastic in a wall. It only traps moisture and promotes mold.

3. Manufacturers of cement backerboard generally recommend that a moisture barrier of some sort to be installed behind the backerboard when used in a wet location. According to some tile contractors, however, this is bad advice. Mold has been found behind the plastic sheeting during remodels. The plastic locks any moisture that gets behind it, and the moisture can’t dry. To properly waterproof a wall, use a liquid-applied membrane on top of the backerboard.

4. Cement boards are a common backing material used due to their immense durability and strength that it provides. Vapor barriers help control how moisture interacts with your materials by preventing moisture from entering critical places, such as inside your walls. The question now is if it’s necessary to have both to increase the longevity of your home. You should only install a vapor barrier on your cement boards with the guidance of an architect or engineer. As much as vapor barriers are good for your home, incorrectly placing them and putting them in unplanned locations can prevent moisture from evaporating and can also cause moisture to be redirected to other areas within your walls.

I'm in St, Louis and I am an engineer. I opted not to use a plastic vapor barrier behind the cement board and the wall studs in my remodel. The original bathroom only had the good old green drywall board behind the tiles.

This is not a recommendation, just differing views on where the vapor barrier, or even if a vapor barrier should be used. Maybe ask some local tile contractors for their recommendation and normal practice for the Milwaukee area.
 
I had a tilesetter tell me that if you use ceramic tile and epoxy grout that the walls can’t leak. He was also drinking a beer at 7am 🤫

But seems to me that the best waterproofing would be done on the outside of the wall, not plastic on the inside of the wall.

As always, I’m a plumber so it’s not a professional opinion.
 
I believe that the tile backer with water resistance built in: Waterproof Backer Board | HardieBacker HydroDefense Cement Board | James Hardie is different than a "vapor barrier" place over insulation.

The latter is standard, traditional practice of placing a vapor barrier on the heated (occupied) side of an insulated wall. Most batt insulation these days has that built in (faced insulation), and most people use and choose that, but I also see the "factory home builders" (those doing large subdivisions) use unfaced insulation, and only a vapor barrier (vizqueen or similar) when local code demands it in a certain area. Here, in NC (just one of the many bizarre building practices I see) they only use a vapor barrier or faced insulation where the insulated wall is part of a garage wall. They rarely use fire-code drywall (type X) but rather two layers of conventional which does the same thing. Don't ask why, I don't know.

The waterproof or highly resistant tile backer saves a step of using "RedGard"; if you use the product noted, you only have to use this kind of waterproofing on the joints and fastener locations. As the RedGard runs about $70/gallon, takes time to apply, you save some money and time by using the pre-waterproofed tile backer.

At least that's the thought!

The tile guys (two Albanian brothers, let's call them Moe and Larry to give you the idea) who were the subs on my bathroom remodel a few years ago were instructed to use an epoxy "super grout". They hated it as it was challenging to work into the grout lines and difficult to clean up, so they said in their broken English.
 
Mitchell-DIY-Guy said:
They rarely use fire-code drywall (type X) but rather two layers of conventional which does the same thing. Don't ask why, I don't know.
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A firewall must be UL listed, and a single layer of fire-code drywall is listed as is a double layer of regular drywall. Even with the labor involved with a double layer of drywall, I would guess the quantity of drywall they purchase, and the fast way they can throw up a sheet, it is probably a cost savings for them with the same results. Of course, the garage is small that way. 🤣
 
I would replace insulation with foam insulation board cut to a nice tight friction fit all the way down to floor. You probably need 1 layer of 1½ and 1 of 2" or whatever combination brings it flush with edge of studs or slightly below then caulk edges with a good silicone caulk wherever possible. Foam in and of itself at that thickness is a perfect vapor barrier and no additional poly needed. Also the huge 10 square feet or more air breech under and behind tub is practically eliminated.
 
What Arctic Trouble said about rigid, foam insulation is a very good plan for bathrooms. Mold can grow on fiberglass & denim batting. One of my bathrooms at home had it.

A suggestion is to spray the studs and back of the existing drywall (back of other room's wall) with quaternary ammonium at 200 - 300 parts per million. Spray the rigid foam, too. If you keep the fiberglass; remove it, ensure no mold is present and spray both sides with the quaternary ammonium. Let it dry before re-installing.

Quaternary Ammonium has what is called a "residual". It will prevent mold, mildew and bacteria from growing forever, or until it is washed off. The reproductive cells of the pathogen either have their DNA disrupted or the cell wall broken, depending on the strain.

By doing this, should moisture sneak in, no mold, mildew or bacteria will grow. Note that, in case you use it for general disinfecting around the home it has residual for certain virus', but not all. It does have residual for all bacterium and mold.

This wall treatment is an often-done step in hospitals, restaurants and other places with moisture potential in closed cavities. Many off-the-shelf products have perfumes, but you can find unscented at restaurant, laboratory & hospital supply stores. (GFS has it, if there's one near you.)

Hope This Helps,
Paul
 
Another option to preclude any moisture from entering the cavity from the bathroom side is the Schluter Kerdi system. It's kind of expensive, but lower cost clones exist.

The Kerdi advantage versus a Red Guard type of product is the lack of out-gassing of VOCs. Out-gassing is a significant concern if there are children, elderly, pets or people with respiratory compromises in the home.
 
Red Guard is also a great tiling membrane for floors with stress cracks. I tiled a 2000 sq ft house, that had a stress crack down the middle. I used a gallon to paint red Guard on the floor 4 tile thicknesses across the floor, so any ground movement would be absorbed by the red Guard without cracking the tile. Did it 12 years ago, and still no cracks in the tile.
 
havasu said:
Red Guard is also a great tiling membrane for floors with stress cracks. I tiled a 2000 sq ft house, that had a stress crack down the middle. I used a gallon to paint red Guard on the floor 4 tile thicknesses across the floor, so any ground movement would be absorbed by the red Guard without cracking the tile. Did it 12 years ago, and still no cracks in the tile.
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I put 3 coats of redguard on the slab in my house. The entire house. I removed all carpet about 12 yrs ago. I like the smell of it 🤡
 
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