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Unread 11-27-2004, 10:50 PM   #1
Dog paws
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CBU in the mortar bed

Dave has an article over on floorbiz concerning the top 5 tile failures. I wanted to ask him a question about it but I can't figure out how to uncombobulate my cookies to post. So I'll ask here.
In the artcle (section #5) he states that putting the CBU into the mortar bed can cause moisture problems. I can see were wicking would occur.
My question is how would the bottom three to four inches of the board be secured to the studs? Could it just be left to hang? Would a silicone caulk on the chloraloy hold up?


Last edited by Dog paws; 11-27-2004 at 11:21 PM.
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Unread 11-28-2004, 03:04 AM   #2
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Michael,i dont believe he is stating that the wicking in and of itself is a problem so much as the wicking without protection to the structural members combined with an improper sloping bed.
First,If you use a vapor barrier and this drops down over the pan liner and the CBU is held in at the bottom by the mud,And you have a proper preslope that will allow the mudbed to actually dry out at the wall area, you will get very little actual wicking because saturation of the mudbed at the walls will not happen.
Second the little bit of wicking you may get will not cause damage due to protection behind the board plus the fact that the board can only grab what moisture is present and if very little remains due to the slope,very little wicking can actually take place.Certainly some wicking is possible,particularly with a very heavily used shower(4-5 showers each and every morning.Or 1 teenage girls shower )limiting the amount of moisture present is the key and the preslope is the way to do that.
Its a shower, we cant eliminate the moisture.We can however control it with sound mechanical practices.Weep holes were designed as a way for moisture to escape the setting bed.Its up to us to get that moisture to the weep holes.Water doesnt run uphill and it certainly doesnt move on the flat other than to spread.I have yet to see a shower area that could be considered perfectly level at the subfloor.water is going to run to one end or corner etc without the preslope.
Daves article is for the benefit of the public, to raise awareness of the need for a preslope in a shower.The number of installers doing showers without a preslope is staggering and it will hurt our industry if damage control isnt done.The CTEF is all about training and improving the marketability of ceramic through education(both public and professional)
Dave and crew are doing a damn fine job, but everything takes time.
Eventually installers will all be doing the preslopes or they wont get the job.Public awareness will dictate it.People are educating themselves more and more with the internet at thier disposal.half trained installers will learn or they will lose thier business's.it's just a matter of time
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Unread 11-28-2004, 08:27 PM   #3
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I really can't differentiate between backer board wicking up water at the bottom and cement mortar (mud) walls wicking up water at the bottom, and the latter has gone on for decades if not centuries. As Todd suggest, the best damage preventative is protecting vulerable wall and framing members.

In my mind no one has come up with an adequate alternative to burying the backer in the floor mud. And further, the board will wick whether it's buried or not. If someone comes up with a cure for the problem we may be able to take steps to eliminate it. Until then we do the best we can with what we have to work with. We need answers, not reiterations of the problem.

Gotta say it, guys. The Schluter Kerdi shower system eliminates the problem entirely by keeping water out of the substrate to begin with.
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Unread 11-28-2004, 08:48 PM   #4
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I really like the Schluter system. We try to do all of our installation that way.

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Unread 11-28-2004, 10:04 PM   #5
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I agree with Todd-- so long as the pan is presloped, there's no way for the CBU to wick moisture-- not for long, anyway. Once the water drains down the pan as a result of the preslope into the weepholes, then what little wicking has occured will occur in reverse, taking the same route out, that got it in, in the first place.

"Whether you think you can, or you think you can't, you're probably right."

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