Air Tight steam shower advise [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : Air Tight steam shower advise

02-26-2008, 08:55 AM
Hello All. I have been slowly buliding a steam shower enclosure for the past couple years. I am a first timer. To date, here is what I have accomplished, but need to confirm my next steps.

The walls:
1 - Shower is located in corner of home so we have two exterior walls.
2 - traditional framing - insulated, plastic vapor barrier then:
3 - green board which is then sealed over with waterproof membrane then:
4 - 1/2" cement board.

Mud pan is in with preslope. I tested prior to putting in the sand mix and all is water tight. Pan does weep water to the drain as its supposed to.

Questions I need to ask:

I have two IC recessed cans in the ceiling. I think I took bad advise from lighting contractor. I am not comfortable with the ability of these fixtures to be air tight. My gut tells me to remove them and put in flush mount, wet location type fixtures. YES/NO?????

Do I need to put a waterproofing membrane on the cement board prior to tiling???

What do I use to seal and make the shower heads, thermo comtrol, and shut offs airtight behind the tile??? Silicone???

Any advise is greatly appreciated

Regards, Joe

Sponsored Links

02-26-2008, 09:07 AM
Your first issue is the use of greenboard. Regardless of the fact there is a roll on membrane on the surface, forced vapor emissions will transmit through that membrane. You need to have a cement backer board such as Durock, Permabase or wonderboard as your substrate. The greenboard needs to be removed. Is most states it is now approved for use in wet areas and certainly is not for use in an area exposed to constant moisture such as a steam shower. The use of an additional membrane over the walls is one that is seen here as taboo by most due to the creation of a possible "moisture sandwich". That is debatable. =)

02-26-2008, 09:10 AM
Welcome, Joe. :)

I sure wouldn't be worrying about those ceiling lights when I had sheetrock sandwiched in my walls. :(

I hate to be a wet blanket, but that's just not gonna work out well.Do I need to put a waterproofing membrane on the cement board prior to tiling???You would normally want a vaporproof membrane over that CBU, including the ceiling.

There are some vaporproof trims that can be had for some recessed lighting fixtures.

Silicone or Urethane caulking can be used around your plumbing penetrations.

But ain't none of that gonna save your sheetrock. What was the thinking behind that part of the installation?

My opinion; worth price charged.

02-26-2008, 09:42 AM
Thank for the input. Just to clarify. The "membrane" over the green board is not a roll-on vapor barrier but a rubberized peal and stick exterior roofing membrane. Totally waterproof. It is about 20 mil. The logic was to use the green board and the roofing membrane to protect to exterior wall insulation. A traditional piece of 6 mil plastic stapled to the studs did not seem to be enough to protect vapor form penetrating to the insulation. I do understand the taboo of not using an additional membrane on the cement board to avoid creating a sandwich. But, isn't a sandwich created with traditional 6 mil plastic-cement board-then roll on membrane?? When I installed the Choroloy, I overlapped the roofing membrane to cover the top edge of the Choroloy sticking it to the greenboard. The entire shower enclosure is covered with the roofing membrane. Filled the pan with water above that line to test it and had no wicking or seeping of water into the green board. Overkill or do I have a do over?????

Thanks Again.


02-26-2008, 10:33 AM
Don't know if your roofing membrane material is a vapor barrier or not, Joe. At 20 mils thickness it certainly could be.

But then you've penetrated it with the fasteners for the installation of your CBU, have you not? And then behind the sheetrock you've installed another vapor barrier material (6mil poly), but it's also penetrated by all the fasteners for the sheetrock and the CBU.

So you've got a pretty effective moisture sandwich with sheetrock inna middle. Vapor from the steam shower will have a great deal of incentive to enter that sandwich area, and not much incentive at all to exit. By and by (think a few years of use) there will be moisture in there with the sheetrock that has no effective way to escape. This is never a good thing.

How long until you see a problem? Can't say. But I'm willing to bet large that you'll have wet sheetrock in the lower portions of that wall in a year or so of regular use.

My opinion; worth price charged.

02-26-2008, 11:04 AM
The rubberized roofing membrane self seals when a fastner is driven/screwed through it. I am not concerned about vapor getting through the screw holes of the roofing membrane . But what you are saying is that I have would a double decker moisture sandwich with the plastic - greenboard - roofing membrane - CBU - then roll on vapor barrier such as Lactite. The entire objective of this sequence was to prevent moisture from getting into the exterior wall cavity.

02-26-2008, 11:08 AM
You may have accomplished that. Still think you have a problem, though.

Did you do the ceiling the same way?

02-26-2008, 11:18 AM
Yes. Ceiling is same, which is the second floor. Blown in insulation above. Per your other post, what prevents moisture from getting into the wall cavity when a plastic vapor barrier is the only thing that used behind the CBU. Aren't the screw/nail holes always created regardless of what is used when the CBU is attached?? What is the recoomended Vapor barrier to use behind the CBU on exterior walls???Should I have used styrofoam insulation instead of batts??? Thanks for all of the input. If I remove the Steam Component, do you feel I will still have a problem, but just prolonged longer??? You've really have me thinking....

Thanks Again, Joe

02-26-2008, 11:30 AM
The vapor barrier comes into play only for steam showers, Joe. For regular showers the poly behind the CBU is a moisture barrier.

The intent is still to keep moisture out of the wall cavity, but the vapor pressure in a regular shower is not as high as in a steam shower and the poly or roofing felt is generally considered sufficient.

If yours were not a steam shower, your wall cavity would be well protected from moisture from the shower. Long term I think you'll still suffer from the poly and roofing membrane sandwiching the sheetrock. How long term? I dunno.

Some folks treat residential steam showers the same as regular showers because "they don't get used much." I don't like that approach. If there is a steam shower available, somebody could use it daily. Still not the same as the room at the local spa, but still enough to create the known problems.

My opinion; worth price charged.

02-26-2008, 11:53 AM
OK. To start over. I need to take down the CBU and then the green board covered with the roofing membrane. Wifey is going to love this one. I am now at 6 mil plastic covering insulation/studs. To rebuild, what is your recommended sequence. I may have to remove the shower pan in order to get the greenboard out that is behind it. May as well start form compete scratch. Thanks for all of your assistance.


02-26-2008, 12:41 PM
Studs. 6 mil plastic. CBU. Steam Room approved membrane which is vapor proofed.

02-26-2008, 12:53 PM
Not me saying it's gotta be torn out, Joe. I'm just trying to give you the theory as I see it. You wanna go with what you've got and see how it works, that's fine. Come back in a few years and educate the rest of us maybe.

I don't agree with Scooter's method, either. I think you should use a real vapor barrier membrane on the inside of the shower and nothing else.

My opinion; worth price charged.

02-26-2008, 01:32 PM
So, full circle. If I leave what I have with steam potential, would you waterproof the CBU before tiling. If I leave as is and remove the steam component/generator so the enclosure is regular shower would you waterproof the CBU before tiling. If I tear out and rebuild from scratch after the divorce... its all moot anyway. Thanks for all of the input. I guess it boils down to the preformance of the roofing membrane and if it can keep any moisture/wetness from penetrating into the green board.


02-26-2008, 02:51 PM
If you have a lot of confidence in that membrane you used, I wouldn't do anything else to the inside of the shower. You'd just start getting into double-decker moisture sandwiches, eh? :)

If you wanna keep what you have, I'd just finish it up. If you wanna kill them two birds, tear it out and hope there's enough dinero left after the divorce to build it again.

But, hell, won't be your house then, anyway, eh? :D

My opinion; worth price charged.

02-26-2008, 03:02 PM
But, hell, won't be your house then, anyway, eh? :lol1:


02-26-2008, 03:51 PM
Peal-n-Seal. 45 mil to be exact. From what I read before I installed it, should offer more than enough protectin to the greenboard. I guess I am confused on one issue will this thread. How is a moisture sandwich not created on an exterior wall. Also, if the membrane that applies to the CBU on the tile side is to prevent moisture penetration fails, without the 6mil traditonal vapor barrier on the studs, the insulation will get damp. SO, with the membrane and the plastic...we have a sandwich. Unless the membrane on CBU is so effective that moisture will not get to the CBU. If that is the case, what does it matter as to what is behind the CBU when the membrane is used. Now I am just plan curious in regards to the steam shower construction as it applies to home building techniques when the shower is located on an exterior wall. Also. I do have plumbing (shower heads) on an exterior wall so it was recommended to separate the plumbing from the exterior studs with some type of partition.

02-26-2008, 04:41 PM
Also, if the membrane that applies to the CBU on the tile side is to prevent moisture penetration fails, without the 6mil traditonal vapor barrier on the studs, the insulation will get damp.The industry and manufacturers' recommendations are not predicated upon product failure, Joe. All I can tell you there.Unless the membrane on CBU is so effective that moisture will not get to the CBU. If that is the case, what does it matter as to what is behind the CBU when the membrane is used.Waterproofing membranes as qualified by ANSI A118,10 are not necessarily vapor barriers. And even those that are can have a perm rating as high as 1.0 in this industry. That means you can still have a bit of moisture entering the wall cavity even if everything is working properly. We're talking a very small amount, but if the exterior of the wall is improperly designed, it can build up in there, 'specially in freezing climates.

Still pays to do the best we can when introducing something like a steam shower on one side of that wall.

My opinion; worth price charged.

And would you please go to the UserCP above, find Edit Signature and enter your first name there so's it'll appear in each post and we don't gotta search for it? :)

04-04-2008, 06:54 PM
I too am somewhat mystified about how to prevent the infamous "moisture sandwich" if your steam shower has one outside wall. Here in the northern latitudes, a vapor barrier is sacrosanct and we would not think of breaching it. Yet, it would seem like most opinions lean toward no poly underneath the cbu, and to only use a vapor membrane on the inside of the shower. I of course did it wrong, but now have to decide if it's worth the risk to leave the poly membrane on the studs as Scooter recommends, or if I will have to backtrack and remove it all. Yikes!

04-05-2008, 04:48 AM
Poor CX has to constantly re-explain himself on a subject which seems to never die :cry:
The only complete system out there that offers the advantage of waterproofing and doubles as a vapour barrier when correctly installed is made by schluter. ie kerdi.
only install ONE vapour barrier! If you want it to also waterproof your shower the you'll have to be creative in tying it in to the rest of the vapour barrier in the house. There should be none behind Kerdi. By the way, if your vapour barrier isn't continuous throughout the house or improperly installed (highly likely) you might as well skip it as it'll do nothin anyways. Vapour retarders behind showers need only be applied if water permeability into the tiled substrate would be an issue. This comes down to choice of materials brother.

P.S. I believe cx deserves credit for his long suffering patience and control in the seemingly never ending quest by some to ask this question over and over and over and over and......................

04-05-2008, 02:24 PM
You are most definitely right Art...I've been lurking on this forum for over a year and can't believe how many patient answers to this question he has provided. My hat is off to the man!
However, I'm a case in point I suppose. Even though I've read hundreds of posts and thought I had a good plan, once you get to a certain point in a steam shower project you end up crossing into new territory and things you thought you had figured out turn out to be slightly more complicated than you initially understood. I wish I knew when I started my project the things I know now! Nothing like 20:20 hindsight I guess...