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Thread: Backerboard questions for cultured marble shower

  1. #16
    DIY Member TWEAK's Avatar
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    Quote Originally Posted by chefwong View Post
    I agree with Tweak with one exception. CBU in any wet application. If you want to take it to another level, CBU with Kerdin.
    I would not do regular sheetrock with Kerdi . If a PRO did it, I would consider it.

    Sheetrock with Kerdi - the variable I see for a DIY is making sure you are sealing the areas where the valve stems, stubs, etc don't penetrate and make the wallboard underneath soft..
    I originally thought CBU with Kerdi as well but Schluter talked me out of it. They are adamant that sheetrock is the way to go. They say if done carefully, no water will get behing the Kerdi. I took their advice, they should know how best to use their stuff. I was very, very careful to get it sealed up, overlapped the Kerdi more than they recommend, etc.

    As far as the penetrations go - I completely agree with you, this is a big concern. What I did was lap the kerdi around and penetration in the sheetrock with liberal use of the kerdifix sealer. My escutcheon/trim for the valve was pretty well sealed to the valve -- but it did have the typical cheesy foam gasket, held on to the back side of the escutcheon with double stick tape - for sealing up against the wall. I removed the gasket, cleaned off the double-stick crap (rolls off easily), coated the gasket with liberal amount of silicone and re-installed. I have an access panel for the plumbing behind the wet wall (it's in the garage for this bathroom - easy!) so I could confirm "no leaks".

    I've since learned that Schluter does make some kerdi "fittings" with rubber seals for the penetrations. I would like to take a look at these to see if they would help, but didn't know about them at the time. The Schluter tech I spoke with didn't mention them, he just advised sealing it all carefully with the kerdifix.

    Water behind the shower is bad news. I've had a slow leak that was totally unnoticed and ended up causing me to put an entire bathroom into a dumpster, build temp walls to allow me to rebuild destroyed load bearing walls, jack up sag in the roof due to the rotten load bearing wall, tear out entire subfloor and floor joists, etc..... so IMO there's no such thing as overkill when it comes to a shower.

  2. #17
    DIY Senior Member chefwong's Avatar
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    One more note after re-reading the OP.

    If you decide to use a vapor barrier, use CBU and then go to town.
    If you decide to use CBU straight, then do CBU with Kerdi (my 1st choice)

    Don't do both - Vapor Barrier, CBU, Kerdi.

    You don't want to create a ~sandiwich~

    I have never spoken to Schulter myself. I have spent as much time as needed digesting info from tile pros and tile pros generally prefer CBU over other bases. They will even go far to say the latter stuff like the hardie board, etc they strongly recommend to not use in Wet Applications and go with CBU if you can.

    And yes, I do think a SUCCESSFUL Sheetrock/Kerdi can be done, I just think the variable where there penetrations, CBU would probably work much better in mitigating the water permeation issue...
    Last edited by chefwong; 04-23-2010 at 02:09 PM.

  3. #18
    DIY Member TWEAK's Avatar
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    Quote Originally Posted by chefwong View Post
    One more note after re-reading the OP.

    If you decide to use a vapor barrier, use CBU and then go to town.
    If you decide to use CBU straight, then do CBU with Kerdi (my 1st choice)

    Don't do both - Vapor Barrier, CBU, Kerdi.

    You don't want to create a ~sandiwich~

    I have never spoken to Schulter myself. I have spent as much time as needed digesting info from tile pros and tile pros generally prefer CBU over other bases. They will even go far to say the latter stuff like the hardie board, etc they strongly recommend to not use in Wet Applications and go with CBU if you can.

    And yes, I do think a SUCCESSFUL Sheetrock/Kerdi can be done, I just think the variable where there penetrations, CBU would probably work much better in mitigating the water permeation issue...
    Good call on the "sandwich". That would not be good. I imagine some people would make that mistake, assuming that if one vapor barrier is good, two would be twice as good!

    As I see it, the bottom line is, when it comes to wet areas we should all do what we believe is the best installation possible. And the one that lets us sleep best. Kerdi is so easy, there is really no reason not to use it or something like it. If you are more comfortable with CBU, use it - it will be fine. No way though, that I would go with just greenboard in *my* home... seen that up close, wasn't pretty.

  4. #19
    DIY Junior Member Pitt's Avatar
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    Thumbs up Cultured Marbel Shower Pan

    - I agree with everything TWEAK said. I have the same type of cultured marble pan originally mention above. My pan does not have a lip or flange. It is a solid base all in one pan. No-caulk drain mounts directly to it. I experienced the deteriorated sealant issue mentioned and subsequent leak.

    - I am currently repairing and I will say from what I observed, you should never use any kind of drywall and Sheetrock behind a cultured marble panel (appearance is it is used for ease of installation not durability). Once it becomes wet it is useless and will start to mildew and has the potential for mold growth if not caught in time. The moisture barrier in this case will be useless as the panel gets wet from the front.

    - One of the newer cement boards with a water tight sealant seams to be the best way to go for durability. I am no expert. I put a liner under my pan to make up for the no lip issue which creates a 6" lip all amount the pan. I will seal between the liner lip and the base with silicone. Then cement board will go up resting inside the lip and sealed to base with silicone followed by cultured marble panel sealed with silicone. Based on what I saw when I removed everything plus what I've read in forums, I'm convinced this is the best route to go for my shower.

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