The exterior wall should have insulation and a vapor barrier of some sort.

The interior walls can be insulated if you like, but they should have a vapor barrier too.

If you want to install a new continuous vapor barrier everywhere, 6-mil poly sheeting is a good and inexpensive choice. Just use a knife and slice and dice the existing vapor barrier.

Durock over the vapor barrier and screwed to the studs is fine, 1/2" thickness for the durock.

The problem is with your floor. Over the subfloor you:
1) lay down a slip sheet, it can be a sheet of the 6-mil poly.
2) Over that nail down expanded diamond mesh.
3) Over that you need a layer of deck mud, sloped to the drain. The slope needs to be UNDER your membrane, not over it. And yes, that's required by code.
4) Over the sloped deckmud goes the membrane. Up the walls 10" is fine. And yes, it gets draped over the curb and only attached to the curb on the outside face of the curb. No fasteners go through the membrane on the inside face or the top of the curb.
5) Over the membrane goes another layer of mud, this will be your tiling base.
6) The curb. A lot of people use stacked 2x4s, that's okay. I make them out of mud. If wood is used, then the membrane is draped over the wood, then a piece of diamond mesh is bent into a "U", turned upside-down, and set over the curb. Again, no fasteners are used on the inside face or the top of the curb. The diamond mesh is then packed with mud to encase the wood/membrane in a layer of mud.

One other thing regarding the curb, you need 2" of elevation between the top of the tiled curb and the top of the shower drain. That's code.

The floor slope has to be a minimum of 1/4" per foot and a max of 1/2" per foot. Also code.

I think Harry Dunbar's photo essay may still be available. Lemme do a google...

Wow, I could have saved myself a lot of typing...but check this out:

Harry Dunbar preslope

Thank you very much! Will show my tile guy this info! A couple more questions: If I am tiling my ceiling, should the vapor barrier be continued there? Also, is it generally the plumber or the tile guy who does the first steps leading up to the membrane being laid?

Mongo, I really do appreciate your help! I decided to gut my bathroom while my husband is away. Think I'm over my head a bit, so your advice has really helped me thru this process. My husband is currently deployed aboard the USS Eisenhower as the Air Wing Commander. I think I saw previous posts where you flew in the Air Force? My husband did a tour at Offutt when based at the Strategic Command. We met some nice Air Force folks while there!

Again, thank you so much! Pam

The ceiling only needs a vapor barrier if you were doing a steam shower.

Plumber versus tile guy on the preslope and membrane...here's where it might get a little sticky.

Local codes usually require the plumber to install the membrane and do the 24-hour water test. Everything else is up in the air.

I know plumbers that do preslopes and membranes. I know other plumbers that have the tiler do the preslope, then the plumber returns to do the membrane, then the tiler returns for the rest of the mud and tile work.

So yeah, that part can be a bit of a scheduling problem.

It depends on what is required by your local jurisdiction and what portion of the job the guys you hire are used to doing.

Some local codes allow the work to be done "under the supervision" of another licensed trade.

That means your tiler could install the membrane himself "under the supervision of the plumber". Supervision doesn't necessarily mean the plumber has to be there watching the tiler install the membrane.

The best bet is to ask your tiler and plumber what their habits are. I don't know where you live or what's allowed in your locale.

The big thing is to make sure that the membrane does indeed hold the same water level for 24 hours, and that when it drains, there are no low spots/dips in the membrane/slope that hold water. Residual wetness of the membrane is fine, but there should be no areas of standing or puddled water.

One minor thing. When using a membrane like you are going with, The membrane gets clamped to the drain. In the drain assembly just above the clamped membrane are small secondary "weep holes", they allow any water that is captured by the membrane and flows down the sloped membrane to travel through the weep holes and down the drain.

After the membrane is installed, the tiler should put a small amunt of something...peas stone, or even tile spacers...in front of the weep holes, then pack mud over the stone or spacers. The goal is to not pack mud into the weep holes, which could clog them. You can see the "stone" against the drain in the illustration below.

The Air Wing Commander on the Eisenhower? Wow, congrats to your family! Yup, I did a stint in the Air Force, flew single-seat for 8 years, got out in '91 after Desert Storm.

Ok. I think I have the general gist now. Thanks! Would you leave all the prep work to the plumber and the tiler? Could a good carpenter look at all of this info and do it? Or would you not recommend that? I think that the plumber I'm using to move my drain said he didn't want to do the membrane, etc. The carpenter will be finishing the framing of the shower this weekend so it'd be perfect just to have him do the first steps while I have him at the house.
Again, really, really appreciate all of your help! Pam

One step always follows another. If you can keep the same person responsible for each step of the project, it usually results in a better job each step of the way and less finger pointing afterwards should something go wrong.

If the carpenter does the deck mud and the plumber does the membrane and the tiler does the tiling, who's responsible for the wavy shower floor that doesn't drain right? The carpenter will point at the tiler who will point at the plumber who will point at the carpenter. It'll be the Three Stooges.

The carpenter can certainly frame the shower, but afterwards if you can keep one person responsible for the remainder of the project, that would be best. My choice would be the tile setter to do the preslope, the membrane and the tiling. The tile setter should be experienced in deck mud preslopes where you might be at the base of the learning curve for the carpenter.

Glad to be of assistance!

Mongo, one question: if we are on slab, how do we attach the diamond mesh over the sheet of poly?

Thanks!