No matter what you do, the entire existing shower will have to be torn down and started from scratch. The reason is that you must have a complete watertight (and vapor tight) envelope before the tile goes on. Far as I'm concerned, the best bet for this is Kerdi. I won't do another steam shower without it.

John,

There are quite a few steam generators that don't have to be pitched down from the generator to the outlet. Most can be installed in a basement below the bathroom.

You do bring up a good point that a few people occasionally overlook, which is to size the generator to both the size of the steam shower as well as the thermal characteristics of the shower.

Personal preference, but I recommend porcelain/ceramic tile instead of stone simply due to vapor drive.

Another personal preference, but I'll take Kerdi over a trowel/roll-on membrane.

If ventilation is provided within a steam shower, it's best to have a dampered vent otherwise steam can travel into the ducting while the steam function is being used, where it will cool and condense. Most won't go to the trouble of adding a dampered vent, in that case it's best to not have any ventilation at all within the shower and instead place it just outside the shower door.

John, to be in compliance with the forum rules on advertising, you need to remove any reference to your business name or logo from your posts.

A liquid applied waterproofing product from Laticrete is much easier to install and more bullet proof for a first time user or even us pros.

Laticrete's system IS a good system. In fact, the PDF file that John referenced in his link actually has pictures from a project I completed back a few years ago at Travelers Insurance Corp. HQ Health Club in Hartford, Ct. just before that booklet was put together. Here's the original picture for the photo on Page 7:

The problem I have with Laticrete's system with reference to steam room and shower applications is that it requires TWO separate membranes-- one a vapor barrier, and the other, the actual waterproof membrane. With Kerdi's system, which to me is as basic as it gets, it's all one surface applied sheet membrane. In most cases, I'll swear by anything Laticrete puts out, including their waterproofing systems. But for something like this, where steam (water vapor) is a concern, Laticrete's waterproofings are NOT vapor proof, and for that reason, I'd rather use the Kerdi.

Personal preference, but I recommend porcelain/ceramic tile instead of stone simply due to vapor drive.

I agree.

An arch designed into the ceiling is nicer looking than trying to achieve the 2" drop per foot required by code in many areas.

It's not just required by code, It's also required by spec-- Both TCNA and ANSI. AS for the arch, it's not a bad idea, except near the peak of the arch where the radius of the arch "flattens" out. That could be a problem.

Wow.. Thank you John, Bill and MongoCT.
Now i wonder if the entire thing becomes a gut job, including the shower pan?
Had hoped to leave the existing ceramic tile in place thinking that the greenboard (is that what that drywall equiv is called???) that is behind the two walls of tile would be a sufficient vapor barrier. And the other two walls with a well constructed glass surround would suffice.
Venting is a good suggestion and do-able.
This is a small bathroom with a window and a standard (not spacious) shower, so the generators i thus far saw seemed ok for the size, and yes claimed that they could be installed below the shower.
Thank you

bicoastal,

Unless it's detailed with a full vapor barrier from the start, it's very difficult to turn a "regular" shower into a steam shower with just a little remodeling.

Traditional showers are normally built with a drainage plain behind the tile/cement board...it might be tar paper, it might be polyethylene sheet plastic...but it's usually "lapped for drainage" instead of being fully sealed at the seams, and it's usually a partial wall installation instead of being floor-to-ceiling and ceiling.

Or there might not be any barrier at all. Just tile over backer board over framing.

A steam shower can drive moisture through natural stone, through grout, and into the wall. If there's not a fully inclusive vapor barrier on all six sides of the steam room cube, then moisture vapor can be driven through the wall and into the wall cavities. When warm moisture vapor cools, it'll condense...wetting and saturating the insulation and/or the wood framing. Not good.

That's why with steam showers it's best to have a fully integral vapor barrier on all sides of the cube. A small yet important point, is that "waterproofing" does not necessarily mean a "vapor" barrier. You can use a waterproofing membrane, and it'll shed liquid water. That's good enough in a traditional shower. But vapor can pass through some waterproofing membranes. Again, that's not good in a steam shower.

Moisture vapor would destroy your green board over time, green board is moisture resistant. Not waterproof. Not vaporproof.

It's been recognized for at least the past 20 years by good tile mechanics that green board is an inferior tile backer in wet areas. Building codes finally caught up to common trade knowledge and banned green board as a tile backer in wet areas in 2006. That said, in a typical shower green board can perform fine or 30 years or fail in 3 years. In a steam shower it'd be a short-lived installation due to repeated vapor drive.

The nice thing about having a topical vapor barrier applied to the face of the tile backer board (between the backer board and the tile) is that the only thing that can get "wet" in a situation like that is the tile and the thinset. The membrane stops the moisture from penetrating into the backer board. With no deep wetting, the steam shower can dry more quickly than otherwise might be possible.

While there are several materials out there that perform fine, you'll see Bill and I mention Kerdi. It's not the only material that can do the job, but it's a warm-fuzzy for me.

It's been my membrane of choice since way back in the 20th century. Wow, that's over a thousand years!

Hi This is very good clarification and yes, I fully understood from earlier exchanges that whatever exists will be not only subpar but unhealthy etc due to mold.
So, we r going to accept gut rebuild of the shower stall, or put in a prefab, or swallow hard and abandon.
Going to cost it out.... Back of the envelope figures indicate that the rebuild so far seems a lot more pricey than the prefab (the shower stall steam doors, the generator etc, of course with far far lovelier results..)
We have a super duper person who helps maintain this cottage and is masterful at many things, so demo and prep work i am confident about and then we and he would likely prefer to use a well experienced person for the essentials of water and vapor barriers, as well as tile. We wont be using Stone, tho the flooring is Blue toned Soapstone large tiles, as ceramic or perhaps glass+ceramic will blend better.
Indeed both in our city establishment and the cottage, all bathrooms pre date 2006 and green board was used. We're pretty careful about water...so thus far, its held well (15 years) but your info quite helpful going forward with renovations.

Hubbest wants to know if you can install vapor barrier over existing tile work, then put new tile over vapor barrier.

If you're talking about putting together a steam shower, you're asking for huge huge trouble, attempting something like that.

One thing you folks need to remember-- a steam shower can literally be deadly to wood frame construction, especially if not done properly. About 6 years ago, I was called into replace one that someone had put together, and by the third shower, these people had their downstairs ceiling crash onto a brand new cherry dining room suite. Destroyed the furniture, and all the antique china in the hutch. It doesn't take much!! If you want to convert an existing shower to a steam shower, THERE IS NO SHORT CUT!! You MUST take everything back to the studs and start from scratch.

So long as it can be a fully enclosed vaporproof and waterproof unit, then it can be done.