I'm doing my bathroom as we speak. Here's my approach. My shower has 2 exterior walls, and my tub and toilet are on exterior walls. My lavatories are on interior walls. All walls are 2x6. My floors will have 1 1/2" gypcrete with pex radiant heating imbedded.

In the shower I have the space to fir-out interior 2x4 walls. I am doing this too build niches for shampoo. My niches will be hardi and kerdi.

First, I plan to use Roxul rock wool insulation in the exterior walls rather than fiberglass batts. I looked at using flash & batt (1+" of closed cell foam plus batts) but the jury is very much out on whether flash & batt is a smart move for my temperature zone (5). Net, net I couldn't justify the expense, plus the issues around in-wall condensation are still a subject of substantial debate.

The next big question is what to use for interior sheathing over the Roxul in the shower. The choices are water resistant drywall, Kerdi-board, hardi-backer, or Durock. A key consideration is how I will waterproof the shower capsule. Speaking with Schluter, they recommend drywall under Kerdi. I'm not sold on Kedi-board (cost / benefit). Also, I'm not a fan of water resistant drywall, so I'm probably going to use Hardi-backer over the Roxul and studs. The thing to be very careful about is Durock and Hardi are very dry and will suck the moisture out of the thinset used to bond the Kerdi to them. Therefore the cementitious boards have to be kept very moist prior to troweling on that thinset. Some folks use a damp sponge to do this. Our approach is to use a garden sprayer filled with cool water (rather than using a squeeze spray bottle).

You'll notice that I didn't mention a vapor barrier over the Roxul. Putting in 6 mil plastic would be a mistake because the Kerdi acts as the vapor barrier. Using both would produce a double vapor barrier - which is an absolute no-no. Keep in mind that your ceiling may be exposed to the attic, so you need to be thoughtful about ceiling vapor handling, if you don't use Kerdi on the ceiling.

On the non-shower walls, I plan to use kerdi over Hardi. In a previous life (as a remodeler many years ago) I have seen too many instances of rotted drywall (green board) and moldy fiberglass batts behind tubs and showers. Hence my roxul, hardi, kerdi sandwich.

On the shower floor, we are using a Pro-line linear drain with (2) 2" outlets. Keep in mind that a 2" outlet will handle ~10 gpm. If you're building a "car wash" type shower you will overwhelm a 2" drain. An alternative is to use a 3" drain & trap. We chose the former approach.

We will be running our pex / gypcrete under the shower floor to produce toasy toes. As we have that solid subfloor, it makes little sense to build a mud pan. Even if I wasn't running pex under I wouldn't do a mud pan. I would use sloped flooring material from Proline or Schluter.

All good tile setters know how to build a mud pan, but IMO that is outdated technology versus the impermeable membranes / drain collars now available in the 21st century.

Hope this helps.

Shower - pick 1 vapor barrier - either the poly or kerdi, not both. No problem with insulation.

Shower pan - either presloped mud base or kerdi tray - not both. The kerdi tray itself is presloped, so you don't want a slope on a slope.

Walls - any drywall or cementboard works. If you are concerned about mold, skip the greenboard and just get paperless drywall. Definitely insulate interior walls for noise control (not temperature). Rockwool works great for this but there are many sound reducing products available.

Floor - Really depends on what type of tile you are putting in and current joist spacing. Ceramic should have the subfloor plus 1/4 cement board mortared and screwed in place. A larger stone tile would be better with an extra layer of plywood laid perpendicular to the subfloor followed by cement board.

Exterior walls - vapor barrier rules vary by region. In cool climates, you typically need a vapor barrier (facing in) on every exterior wall.

Walls - any drywall or cementboard works. If you are concerned about mold, skip the greenboard and just get paperless drywall.

You can only use drywall IF you are using a surface applied membrane like Kerdi. And if you use Kerdi you really should use the complete system with the special Kerdi drain.

If you are doing a "traditional" shower with pre-slope, clamping drain and liner you will need to use cement board, either with poly behind or waterproofing applied to the surface.

Thank you all for taking the time to answer my questions. I greatly appreciate it.

"You can only use drywall IF you are using a surface applied membrane like Kerdi. "

Huh? The OP was asking about what to do with the rest of the bathroom walls separately from the shower. Drywall is perfectly acceptable to tile over outside of wet areas.

Sorry, I missed that.

For me,

Anywhere I want a "waterproof" surface covering (tile, stone, synthetic) it's kerdi on the walls over hardi, and kerdi over quick slope (from proline) on the shower floor. Tub deck is kerdi over hardi over plywood.

Still waiting for someone to convince me of a better 21st century solution. Green board, mud pans, denshield are inferior alternatives but still widely practiced for reasons of cost or tradition...

My approach takes more time for sure, hence my alias:-)

Hope this helps!

NJHM-- On the Gallery side of this forum, I've listed an FAQ that would answer most, if not all, of your questions.

If you want to read it with a little more order to it, I've put it together in a little more order of evolution on my website:

Here is a link that might be useful: My FAQ page

Bill V, I haven't seen your post for a while. You must be busy. Glad to see your link and I will check out.

Busier'n hell. :-) This is the first weekend I haven't worked in months, and they even wanted me working THIS weekend. I told my customer if they wanted to provide me AND PAY FOR a good divorce attorney, I'd THINK about it. That ended the discussion. :-)

Drywall all walls.
3/4" plywood the floors

Kerdi all wet areas, then tile.
Ditra the dry floors, then tile.

Keep it simple, solid and leak proof.

Bill, thank you. I will check out the FAQ page. I hope it has something on Ditra in there. I met a couple of tile setters this past Friday and they suggested Ditra in the non-wet bathroom areas and kitchen. They both also said that Kerdi will not work in my shower layout so it will have to be a mud job with Laticrete products for waterproofing (Hydroban). I don't know anything about Ditra so that will be something I need to learn about now.

Pharaoh, Thank you for taking the time.

Actually, EITHER system (Kerdi OR Hydroban) can be used over a mud pan, and in fact, as much as I've used both systems, I've yet to EVER use the pan tray. That said, though, ALL my showers now are Hydroban, if for no other reason than the fact that they're completely seamless. No build up from layers of membrane in the corners is a another plus. The ONLY time I'd consider using Kerdi now is for a steam shower, being that with Hydroban, you need a separate vapor barrier, and with Kerdi, you don't.

As for using Ditra in areas other thanwet areas, I know several installers that use Ditra for ALL their flooring underlayment needs, completely replacing all floor backerboard with it. I DO believe it's got its place, but I'm not ready to pass on the extra expense of Ditra over backerboard just because. I'll use it where it's warranted, and that's it. It IS okay to do it, though, mechanically speaking.

I'm sorry for the delayed response. Thank you all for responding to my questions and concerns.

I changed the foam insulation to rockwool. None of the tile guys that came to give me estimates like Durock but I decided to stick with it in the tiled (wet) areas.

Bill, I checked out your FAQs page. Its wonderful and helped out in better understanding the various components of tile laying. I kept a hard copy in my car for future reference since I will definitely get confused between the different types of thinsets.

On 5/13/12 Pharaoh wrote:

Drywall all walls.
3/4" plywood the floors
Kerdi all wet areas, then tile.
Ditra the dry floors, then tile.

Keep it simple, solid and leak proof.

Is this still the short answer? I want to be able to ask the contractors I'm considering the right questions, and hopefully already know the right answers.

Kerdi and Hardiboard do not play well together ! ! !

This post was edited by xedos on Thu, May 29, 14 at 12:43