Had some idle brain time, got to thinking about odd thoughts …
So when you build a proper tub/shower enclosure, there’s a waterproof membrane on the wall that laps over the lip of the tub. The purpose for the lap is in case any moisture gets behind the tile, it will drip down the WP membrane on to the tub flange and into the tub, then down the drain. So what happens when the moisture meets the caulk joint between the tile and the tub? Where does it go?
“When asked if you can do something, tell’em “Why certainly I can”, then get busy and find a way to do it.” T. Roosevelt
Replies
Same as what happens with 'sealed' attics and double vapor barriers in walls, the water fairy waves her magic wand and it 'goes away'.
Of course, if the water fairy fails to arrive in time, her schedule is busy so she is not really reliable, the interior surfaces stay wet and wood rots, plaster disintegrates and/or mould takes over.
Man has yet to produce a structure which will stay totally dry for long. IMHO a wise builder is one that builds as tight and dry as possible but plans that some time in the future water will make its way in. Understanding this they make plans for the water coming out.
It sits on the ledge of the tub or goes into the tub. That ledge couldn't hold more than a few drops per inch.
Regards,
Scooter
"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Good question, Ed.
Weep holes? Haven't seen them yet.
If it's that much water the bottom row of tiles will let you know.
I'm not worried.
What you're saying makes sense but I think what actually happens is that the CBU (or mortar) behind the tile might stay slightly damp. I don't imagine drops of water running down the poly/felt behind the CBU, unless someone did something ignorant and there's a leak in the installation. Grout is porous and moisture will travel thru it, but I think it would have to be a helluva lot of it to actually run down the moisture barrier and get trapped at the bottom, behind the caulk.
Besides, the caulk is only the bottom 1/8" or so, and moisture could migrate thru the grout just above that level.
I just did one last week and was thinking about this. I've torn a lot of them out and never seen evidence of that particular problem, although I've certainly seen damage from water leaks where a shower pan failed, or where greenboard was used. Maybe the CBU over poly method is new enough that we don't really know? I had some thoughts about using a waterproofing membrane over the CBU, but want to research this more before doing it. Seems like it might be a good idea, and would add maybe $75-100 to the average 5' tub/shower with 5' high walls.
Our last house had a tile shower where the mortar bed was applied over wood lath, and it lasted about 75 years. There was no evidence of wet lath when I took that one apart to remodel.
I got lucky: my builder didn't use a WP membrane in the first place. As such, the water goes all over the place, like downstairs into the first floor's ceiling.
How is that much water getting behind the tile??
Murphy's law. Actually, it has to do with the pressure differential. The water pressure on the shower side is high and on the backside, it's low. Water will naturally want to migrate through the wall. The best designs will assume their installation will fail and make accommodations for the failure. To caulk the bottom of the wall to the tub ensures any trapped moisture will have no opportunity to drain.
BTW-a significant area of leakage is around the shower handle and tub spout. Both of these are under a constant deluge of water. I feel the top 270 degrees of both of these penetrations should be caulked. I leave the bottom open with the hope that any water that does manage to penetrate can drain. The caulk can be applied to the backside of the device so it is not visible to the user. Also, please use a kitchen and bath sealant. These sealants have a mildewicide to keep them looking clean.
BTW-the best source of leaks in a shower? A built-in shelf. I have never seen a shelf not leak.
Certified boat fetish.
How do you figure the pressure inside a wall is lower than the pressure in the building??
Thats called an "Early Alert System".
Some guys get big bucks for that.
; )
J. D. Reynolds
Home Improvements
This is why some people do not like to use a wp membrane behind the tile substrate.
Personally, I do not. (this could launch a debate)
I use durock, good tiles, a good quality grout w/ admix, and then seal it when done.
After all it is a vertical surface. Not like water is sitting on it for a long time looking for a tiny hole to get through. Any miniscule amount of moisture that makes it through is free to dissipate into the air cavity.
I pretty much agree with you. I think that in most cases, simply flashing the studs would be adequate, and that a full moisture barrier behind the CBU is not necessary. In a house with one shower, no window, no fan, and four teenage girls, I'd go with the full treatment.
In a house with one shower, no window, no fan, and four teenage girls, I'd go with the full treatment.
LOL Agreed.....weep holes and all!