water permeability of CBU's [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile

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klarck
06-05-2004, 05:42 PM
It only takes a couple days of lurking this forum to have it on good authority that Durock/Wonderboard boards are water resistant, but are water permeable. Hence the advice to always use a moisture barrier. Okay - so I'm using 15 lb roofing felt or 4 mil poly behind my Durock, lapped so it sheds water down into the lip of the bathtub.

I'm interested in the dynamics of the system so often prescribed here. Given tile+grout+thinset+Durock+roofing felt in a shower surround, how much water is really going to reach the roofing felt? How many showers over what period of time do I have to take to get water past the durock? Does the barrier condense vapor, or is it redirecting seaping water? Are corners any more vulnerable than flat surfaces? Do vertical surfaces behave much differently that horizontal ceilings or shelves? Does the Durock eventually become somewhat permanently saturated? Does it wick water somewhat uniformly like a sponge? Does it eventually dry out - if so how long does that take?

Yep, I ask a lot of questions. What I'm really trying to get at is: How much water works its way through tiled walls, how does it move, and how fast?

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Jason_Butler
06-05-2004, 05:55 PM
I don't think the issues are really with the "walls". Water from the mudbed will wick up the CBU a bit. I've done some experiments with CBU immersed in a bucket of water. Never seen it climb more than 5-6". Others have identified water at much higher elevations but that was likely due to cracked grout or very porous tiles.

Alot of installs these days are using porcelain tiles which are very water resistant. Not much ( if any ) water will get through those tiles. The grout is a different story. Sealing grout will help alot but water will travel freely through unsealed grout. How much? hard to say.

Flat surfaces, like benches, will take on alot of direct water. These are the most risky areas in my opinion and should be waterproofed prior to tiling.

I guess the short answer is , it depends on the install. But, we are focused on the "what if's". We like to plan for the worst and hope for the best.

I just tore out a 10 year old shower with the standard 4" wall tile. Durock was use behind the tile as was the vapor barrier. It was unfortunate that the plastic shower receptor failed. The tile part of the shower was done right and showed no signs of water at all - even though the tile was not porcelain.

I'm sure John has more stories, but I haven't seen much water permeate the walls.

Jason

Davy
06-05-2004, 09:06 PM
I don't think much moisture gets thru the CBU around a tubsplash but the bottom 18 inches of a shower stall is different. Like Jason said, the vulnerable areas are the seat and curb.;)

Davestone
06-05-2004, 09:08 PM
I too have seen no saturated cbu tearouts on walls,only in bad pans.

Gil Smith
06-06-2004, 02:21 AM
Are corners any more vulnerable than flat surfaces? I can't tell you if they're "more vulnerable", but logic dictates to me that vertical corners are especially vulnerable to moisture penetration. There will always be a seam between adjoining cbu panels coincidental with a grout line in every corner, providing a path of little resistance. I believe special attention is warranted to assure the integrity of a continuous, unbroken moisture barrier around these corners to insure that no water reaches framing. I went to the extent of laying a strip of Moistop brick flashing from ceiling to just below the top of the pan liner in all my vertical corners.

Horizontal seams can't be ignored but IMO there's not as much of an issue with integrity of the moisture barrier in that regard.

The only horizontal cbu surfaces in my shower are in the bottoms of niches, and I waterproofed those (and sloped them to drain as well), as there was no other practical way to prevent water penetration and ultimate contact with framing.

Like many others I've performed the cbu-in-a-bucket-of-water test, and have seen the water wick only a few inches up the cbu. This is not however, representative of the cbu sandwiched in a shower wall between a moisture barrier and tile, and I'm not at all sure that the wicking in free air is not limited by evaporation.

Therefore, I waterproofed my cbu on the bottom edge and on the inside wall for the first few inches from the floor. I was careful not to waterproof the back side because I wanted an outlet for any water that permeated the cbu. I'm not sure it was necessary, but I took an extra step of caulking the space between the cbu and the pan liner, and made weep holes in the caulk every few inches to allow water to pass from the back side of the cbu to the drain.

I believe this should virtually eliminate the possibility of wicking due to contact between the cbu and the water-laden tile bed.

I'm hoping this shower doesn't get torn out in my lifetime, so I'll probably never know for sure. ;)

John Bridge
06-06-2004, 02:47 PM
Hi Klarck, Welcome aboard.

You gotta be some sort of engineer, right? :)

I go along with what's been said. I don't have any date whatever. Tub substrates do get wet, though, but in the case of cement backer board, I think they dry out just as fast. Sheetrock behind tile gets wet and stays wet because it doesn't give up water to evaporation. Anyway, I don't think you have much to worry about.

AND, if you dry the shower after each use, water will never even have a chance to penetrate the tile and grout. ;)

klarck
06-06-2004, 05:11 PM
Thanks for the good information. I've always admired field guys who conduct experiments and keep a good forensic eye out. That feedback is gold.

And, why yes, I am an engineer. In designing the nominal system, I like to know where the ragged edges of performance lie. Really though, it's not like I'm trying to make a shower surround that could stand up to a fire hose......well - not yet, anyway.

John Bridge
06-06-2004, 05:53 PM
Yes you are! :D

Mike In Va
12-28-2004, 09:01 PM
I thoroughly read the 1/2 " Durock installation instructions before installing it in my Tub/Shower surround and there was no mention of a vapor barrier being needed?? I taped and thinset the joints, skim coated the entire installation and now Im ready to tile. Do I need to tear it all out??

Jason_Butler
12-28-2004, 09:09 PM
Assuming you have a "tub surround" and not a full blown shower, you will likely not have any issue. To be on the very safe side, you can apply Redgard over the CBU. It is a "paint on" waterproofer. This will guarantee a bulletproof install.

Now to the instructions on Durock and most other CBUs...

The vapor barrier has no impact on the performance of the CBU itself - hence the choice by the manufacturer to omit this. Admittedly, there is some debate within the tile community as to the need for a vapor barrier. Makes sense to me...keeps water from getting into the walls.

If it was my install @ this stage...I'd coat it with Redgard and sleep really well at night - cheap insurance

Jason

e3
12-28-2004, 09:13 PM
there are many reports of people removing caulk or sealant from around perimeters and water , drain's out that was trapped in the wall .
There is also talk of need for weeps to avoid this .

DreamQueen
12-29-2004, 02:38 PM
The only horizontal cbu surfaces in my shower are in the bottoms of niches, and I waterproofed those (and sloped them to drain as well), as there was no other practical way to prevent water penetration and ultimate contact with framing. If you built the niches from CBU, did you pack and tape all the seams?

Dream :)

DreamQueen
12-29-2004, 02:41 PM
there are many reports of people removing caulk or sealant from around perimeters and water , drain's out that was trapped in the wall .
There is also talk of need for weeps to avoid this .

Which perimeters would they be? tub showers also?

Dream :)

Scot Thompson
01-01-2005, 11:28 PM
Water is unlikely to rise any higher in the CBU's for a very good reason - surface tension (capillary action). Surface tension is the same force that causes smallish objects like paper clips or bugs to float on the top of water. It's the same reason if you look at water inside a small tube (for example, a manometer or liquid level) it has a curved surface.

For an air-water interface, the surface tension of (pure) water would be about 0.073 N/m (or about 0.005 lb/ft for those of us who don't know what a Newton is). It's less for impure water and several common showering chemicals (Soap!) reduce it even more. For the worst possible case, let's assume it's pure.

The key is that the height of the rise in the material is related to it's pore size. Larger pores will not support much rise, while smaller pores allow the water to rise higher.

I'm ignoring the angle of friction - it's a better case anyway.

So, the formula looks like this (of course, all your units have to match):

h = ( 4 * σ ) / ( φ * d )

where h is the height of water rise
σ is the surface tension force
φ is the specific weight of water
and d is the pore diameter

What does all that crap mean? Well, I assumed the pore size was 1 mil, or about 0.25 mm. Water should rise about 119 mm or about 4.7 inches. Which tends to correspond to observations others have made in this thread.

Since the surface tension is what is causing water to rise in the CBU's, that also means it would not be affected by being packaged up inside the vapor barrier, thinset, tile, grout, etc. Therefore, as long as there are no other sources of water into the CBU other than the bottom, the water shouldn't ever go higher than about 5 inches up. If there ARE other sources, it would be 5 inches higher than those sources.

Well, that's enough for one night :)

Mike2
01-01-2005, 11:38 PM
What's a good first name for us to use klarck.

Seems to me there's another aspect of this vapor barrier question that has not been touched upon, i.e., condensation. Warm moist air from the shower environment meets cooler air in the stud bay. Drip, drip...adds up in time. :)

jadnashua
01-01-2005, 11:39 PM
A reply after my own heart!

Chris the Rep
01-02-2005, 03:32 AM
What's a good first name for us to use klarck.

Seems to me there's another aspect of this vapor barrier question that has not been touched upon, i.e., condensation. Warm moist air from the shower environment meets cooler air in the stud bay. Drip, drip...adds up in time. :)

I can cite first hand experience on a similar situation in the showers in a golf club. There is no blame here, and no reason to rehash the mastic in showers discussion...

Showers were built and framing was covered with CBU which was then waterproofed with a trowel applied membrane, since no vapor barrier was specified. Tile contractor then installs 4 1/4" matte glaze to the shower walls with Type 1 mastic. Turns out that a vapor barrier had been installed on the exterior of the framing between the sheathing and the insulation. Within 3 months tiles started to pop off along the 2 lower courses, and I get a call about the defective mastic.

I went in and looked at it and took off a few more tiles. The mastic was soft, but the membrane was absolute mush. I probed it a bit with the awl on my knife and pushed a small hole through the CBU. Water gushed forth like a spring. What happened is that water vapor passed throught the membrane, condensed on the poly and became liquid water again. The membrane also worked from the reverse, and would not allow this liquid water to pass back through, so the stud cavities filled up with water.

I remember this, and I think that sometimes there is not enough dinstinction drawn between a waterproof membrane and a vapor barrier. Although they are similar, they are not necessarily interchangeable, thus the need to be cautious about terminology.

Chris

DreamQueen
01-02-2005, 10:11 AM
I'm confused. Why would water pass through the waterproof membrane which was applied over the CBU?

Anne :)

e3
01-02-2005, 10:16 AM
not all membranes are vapor- proff
check with the mfg. of the membrane they should test to a standard like ASTM E96 e

DreamQueen
01-02-2005, 10:17 AM
there are many reports of people removing caulk or sealant from around perimeters and water , drain's out that was trapped in the wall .
There is also talk of need for weeps to avoid this .can you clarify on this? thanks.

Anne :)

e3
01-02-2005, 10:21 AM
when the joint around the base is caulked any water or vapor that gets though the board can build up between the wall and the membrane.It cannt drain out.By simply living a weep can solve the problem.

DreamQueen
01-02-2005, 10:22 AM
Seems to me there's another aspect of this vapor barrier question that has not been touched upon, i.e., condensation. Warm moist air from the shower environment meets cooler air in the stud bay. Drip, drip...adds up in time. :)And so, what is supposed to happen to the condensation? That would be with poly, not felt?

Anne :)

DreamQueen
01-02-2005, 10:26 AM
when the joint around the base is caulked any water or vapor that gets though the board can build up between the wall and the membrane.It cannt drain out.By simply living a weep can solve the problem.Hi Eric, So where would one leave a weep hole on a tub/shower -- I've got no vapor barrier. Wouldn't water get in thru the weep hole and drain somewhere? Sorry, I'm learning.

Thanks,

Anne :)

DreamQueen
01-02-2005, 10:27 AM
not all membranes are vapor- proff
check with the mfg. of the membrane they should test to a standard like ASTM E96 eOK, so water can't pass thru but vapor can. Things can get very technical.

Thanks,

Anne :)

e3
01-02-2005, 10:30 AM
you should have a membrane behind the wall board. Where the membrane flashes over the lip of the tubs flange leave a small opening so any water that gets though the wall ,trapped by the membrane can drain out.If you dont have a membrane its mute but you have a problem brewing.

DreamQueen
01-02-2005, 10:44 AM
Where the membrane flashes over the lip of the tubs flange leave a small opening so any water that gets though the wall ,trapped by the membrane can drain out.Ah so, sure, excellent :bang:
If you dont have a membrane its mute but you have a problem brewing.That's moot ;). Yes, it's too late. Not my choice and I didn't learn of them until investigating a problem in the tile job. My installation is a professional example of everything not to do :cry:.

Thanks,

Anne :)

e3
01-02-2005, 10:56 AM
are you done with it? tile in ?

DreamQueen
01-02-2005, 11:02 AM
Yes, unfortunately, essentially all the tile is up, ungrouted, and it was expensive. Just sitting there waiting for a repairman if I'm lucky enough to find one (a few things have to be changed).

Anne :)

e3
01-02-2005, 11:25 AM
this is a MAYBE !! epoxy grout??? anyone ??