I’ve been reading on JLC and Johnbridge, and I’m now confused as to what is best practice with respect to tile backing for a shower. We don’t install tile, but we do hang the backing for tile on our jobs, so this is pretty relevant.
Our installer hangs Durock without any kind of barrier behind it, and apparently this isn’t good. But I don’t see how 15# felt would help much: it’d be penetrated by each screw through the Durock, so wouldn’t each screw wick moisture right into a stud? Or are the penetrations insignificant, just like polyethylene VB for exterior walls?
The drywallers on JLC seem to advocate using Densarmor, but I don’t understand how it differs from Durock as a tile backer.
The folks over at John Bridge are in love with the Schluter Kerdi system, which is an entirely different ball of wax and something we’ll never get into.
Thanks in advance.
Replies
Water can pass through grout. Even if it's sealed. No, it's not like a sieve, but over time it can happen, and it does.
Water can pass through natural stone and through and cracks/pinholes in the grout. Again, not a substantial amount, but over time...it can. Even if it's sealed.
Remember, most stone and grout sealers are not impermeable layers, they allow vapor transmission through the sealer.
So, all that theoretical crap aside...
Water can get behind the grout and tile. When it does, where will it go? Into the tile substrate.
Greenboard used to be an approved substrate for tile in wet areas. Years and years of failed installations finally convinced the code makers that be that greenboard, while moisture resistant, is not waterproof. And why did the greenboard fail? Due to repeated and long-term exposure to water that got behind the tile and grout.
(note the recurring theme)
Cement boards like Durock and Wonderboard, and fibercement, like Hardie? They will get wet, but they don't rot and disintegrate when wet like gypsum boards do.
Those three, however, will allow water to pass through them, and then with no barrier it'll get into the framing bays. Rotted framing, mold, mildew, etc.
Add a barrier like 6-mil poly or lapped tar paper? That's the right thing to do. It's not neccessarily a vapor barrier per se, but more like a drainage plane.
Water vapor that gets past the tile and grout and through the cement board will then hit the poly or felt. It's prevented from getting into the framing. Any moisture that hits the felt may eventually dry back out through the grout lines and into the shower...or it may condense out and flow down to the flange. Or in a shower, it flow to the secondary weep hole sin the 2-part clamping drain.
In tub surrounds, some people (no one I know) leave weep holes, most caulk the tile to the tub flange. I've been told that any moisture that does flow down will eventually dry through the grout back into the bath.
With nothing organic between the poly and the tile, there is nothing to feed mold or mildew, and with any water only hitting cement board or thinset, etc, there is nothing to rot away.
Screws or staple holes won't wick water, as there's nothing substantial to wick.
You mentioned "DensArmor." Never should Densarmor be used a a tile substrate in a wet environment. Never. DA is not approved as a tile backer in wet areas, it's a paperless drywall designed for applications in more humid areas like baths and basements. But not as a tile backer in wet areas. It'll disintegrate.
DenShield? It may be what you're thinking of. DS has a modified gypsum core. Instead of a paper facing like regular drywall or paperless like densarmor, though, it has an acrylic facing. So the facing on DenShield is impervious to water penetration. Screw holes and cut edges, however, is another story. Water that gets to the gypsum core through any penetrations in the facing or cut edges can wet and disintegrate the board from within.
Lastly (and it's about time I got to "lastly"...there is also a "DensArmor Plus."
DA Plus is like Densarmor, but it has an acrylic facing on one side of the sheet, and that acrylic facing is designed to face the stud cavity, not the living space.
So, while DS and DAPlus have glass facings that will face the interior of the wall, only DS has a second plastic facing that faces the living space. DS is intended as a tile backer in wet areas. DA Plus is not.
Make sense? Heck, I wrote it and I'm confused...<g>
Most drywallers I know dislike Densarmor due to the itchy nature of the glass fibers withing the paperless sheets.
Most tilers I know prefer cement board because they consider DenShield to be crap as a tile backer in wet areas.
The most conscientious tilers? They use Kerdi.
Kerdi? Once you go Kerdi, you'll never go back. Great stuff.
Mongo
Edited 8/19/2007 3:04 pm ET by Mongo
HUH?
(G)
With nothing organic between the poly and the tile, there is nothing to feed mold or mildew, and with any water only hitting cement board or thinset, etc, there is nothing to rot away.
Does mastic (Tec Double Duty and similar) used for wall tiles support mold growth?
Thinset only for wet locations. Bagged dry mix too, not the crappy pre-mix in a pail.[email protected]
"Does mastic (Tec Double Duty and similar) used for wall tiles support mold growth?"
In a shower it's a moot point, as Type I and II mastics are at best rated for "intermittant" water contact.
Not suitable for wet areas like showers and tub surrounds.
If they get wet, they soften and creep. They'll support mold and mildew, but not the tile.
Mongo
Yeah, what Mongo said. Unless the tile is failing (as when placed on drywall) and large cracks have opened in the grout, the moisture that gets though generally isn't liquid drops of water but rather "wicking" moisture.
If you place cement board directly against framing, moisture will wick through the cement board and into the framing, keeping it perpetually damp. Provide any sort of non-porous layer between cement board and framing (could be builder's felt, plastic, rubber, metal, etc) and water won't wick through, keeping the framing reasonably dry.
There's less need for an actual "barrier" to water, since we're primarily dealing with wicking water, so liquid water is unlikely to form on the back side of the cement board. (The major exceptions, in a properly constructed shower, are the floor -- obviously -- and spots where a strong stream of water may impinge on the tile -- eg, the wall opposite the shower head in a very small shower.)
Thanks guys. That clears it up. I'll make sure that our guy uses tar paper behind the CBU.We do very few tile showers (2 in the last year), but I'm glad to be better educated.
Edited 8/19/2007 4:37 pm ET by Biff_Loman
are you saying that you install the board after the plumber has set the vinyl pan liner and drain ?
carpenter in transition
Wow, all this discussion makes you want to be a brain surgeon where it isn't so technical. Can someone simplify all this to some simple practices? I am doing a shower (actually a steam room also) and I do need to take care of the moisture issue. How does this sound to you:
1. Install rubber mat on top of floor plywood. Tie mat to drain screw cap so that any water that gets to the mat can wick to the drain.
2. Wrap the rubber mat up the shower walls at minimum 6" overlap. Place (staple?) rubber mat on the 2x6" studs on all walls and ceiling (can I substitute rubber mats on walls with 60 minute roofing papers?)
3. Place cement boards on the walls over the rubber mats. Pour mortar base on shower floor about 3" thick with proper slope to drain.
4. "Seal" seams between cement boards with thinset.
5. Tile over the cement boards.
This is a safe application? Where can I improve?
Thanks.
U can start with step one ...
and do a preslope before U lay the mat.
lotsa more than that ... steam showers are more complicated than a basic shower.
Buy the Byrnes book ... and the Bridges book.
read both ...
Jeff Buck Construction
Artistry In Carpentry
Pittsburgh Pa
What product is "rubber mat" ?
As Jeff said, you have to build your pan in layers.
The slope is built into the first layer, then the membrane, then more base.
Pour mortar base on shower floor
There is no pouring base, it's dry dry dry mix that you pack to the slope.
Your flat floor will accumulate water that will not flow to the drain, and eventually stink.
Wow, all this discussion makes you want to be a brain surgeon where it isn't so technical.
It's not brain surgery, but if you screw it up from the get-go like you have it planned now, you're gonna need wallet surgery to fix your screw up.
No offense, but your post makes it obvious you do not know how to do this. It's a big expensive project that has to be done right at every stage, there is no going back to fix anything.
It's a complete tearout & start from scratch to fix if done as you have outlined.
Joe H
One thing to understand is that there are about a half-dozen different (and reasonably valid) basic schemes for doing a shower. And of course about ten thousand ways to do it wrong. Most folks here who work with the stuff have their favorite schemes, and that's where they're coming from with their descriptions. Plus, in any informal description here there are always steps that are omitted because they're "obvious". If you try to pick bits and pieces from different people you end up with a hodge-podge that may or may not work.You're better off getting a good book on the topic, studying it fairly closely, and then following the book's process pretty much to the letter.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Howdy,I've actually worked on the surgical team for some brain surgeries. Setting tile, even for a steam shower, is a cake-walk in comparison. :-)And the consequences for setting tile incorrectly are far less severe...Glen
Check out the Michael Byrne and John Bridge books here:
http://tinyurl.com/2jclgg
And this thread on Kerdi walls and floor here: http://forums.taunton.com/tp-breaktime/messages?msg=86714.1
You should check out the "Small Addition" thread in the photo gallery as well for another fine Kerdi job. http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=79773.1&maxT=12
As Dan mentioned above, there are a bunch of ways to do it wrong and make an unholy mess. I've got a house with a 3 year old standing shower built on greenboard, and a leaky pan. Do yourself or your client a favor and do the best job possible.
Jeff gave you good info that the floor membrane has to go on TOP of the preslope, not under it.For a steam shower you need a continuously sealed barrier behind the tile (ceiling, walls and floor) to prevent water vapor from getting into the framing bays.The BEST way to do that is with Schluter's Kerdi system. It's actually the easist, too.If you go with a CPVC or CPE floor membrane, review your numbers for carrying the membrane up the walls. Your numbers don't meet code.Mongo
We only do this when there we sell a pre-fab cultured marble or acrylic shower base. If the client wants a tile floor for their shower, we point them in the direction of a tile-setter and wish them well.Virtually all our jobs have cultured marble panels for the walls. It's our preference.
Edited 8/20/2007 5:42 pm ET by Biff_Loman
I've done a couple kerdi jobs and love it. Its a little more work than cement board, but a more bullet proof system. You could probably set yourself apart from the competition by offering this.
Kevin
Kerdi
sully