City of Palo Alto rejects any drywall in wet areas - suggestions for backing?

Discussion in 'Shower & Bathtub Forum & Blog' started by rap, Mar 21, 2012.

  1. rap

    rap New Member

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    The Building Dept of Palo Alto rejects the use of green or any other drywall in wet areas. To achieve a S&C floated surface for tile, what other backing suggestions would you recommend? Perhaps a Two-Coat float over mesh and 15 lb felt?
  2. cacher_chick

    cacher_chick Test, Don't Guess!

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    Everyone in the country is using cement board, or some variation of it.
    It's been this way for a quite a few years now.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    They seem to be oblivious that if a waterPROOF surface membrane is applied properly, the drywall is NOT in a wet area. But, trying to talk sense into some people is useless. The only thing I'd consider is to show them the TCNA method approval that allows it. But, as said, it's based on a proper install. You do what you have to, so cbu, while harder and more expensive, is usable underneath any of the surface membrane materials, either painted on or those in sheets. Note, not all sheet membranes support drywall - the TCNA procedure references the manufacturer's recommendations. Kerdi, for one, prefers this, but is equally viable over other backing materials to meet local ammendments to the TCNA procedure. I guess the thousands of installs that are in great shape has no credence...fighting city hall is possible, but sometimes not worth the effort when a viable alternative is available.
  4. dlarrivee

    dlarrivee New Member

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    Jim we both know that people expect to hang board and tile right over it, I'm sure that is why the county is not allowing it.

    What about fibreglass faced gypsum board?
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Seams where it's been cut are still problematic unless it's properly waterproofed. guess you just have to ask them what they'll allow.
  6. dlarrivee

    dlarrivee New Member

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    Problematic how?

    You could use fibreglass faced drywall everywhere in a bathroom, waterproof the wet areas, and skim coat the rest.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    While fiberglass may not be mold food, if you get gypsum wet, it can turn to mush, so any seam has the potential of being a problem...depends on how well you put things together, but it's not cbu which doesn't really care if it gets wet.
  8. jimbo

    jimbo Plumber

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    If by wet area you mean the shower, it has not been approved for 20 years to use any kind of drywall under tile. It MOIST areas, like the walls and ceilings in a bathroom, they came out with the "greenboard" but it really was not the answer. They do now have blueboard, which does not support mold growth, but it is not water resistant. Use cement board, or actual lath and mortar, under tile in showers and on the floor.
  9. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    Post(s) deleted by John Whipple
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  10. dlarrivee

    dlarrivee New Member

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    Be careful, if I didn't know any better I would say that John makes more money promoting products on the internet than he does remodeling bathrooms.
  11. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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  12. dlarrivee

    dlarrivee New Member

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    Are you related to Billy Mays?
  13. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    Post(s) deleted by John Whipple
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  14. rap

    rap New Member

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    Thanks for your replies, but i'm not much further ahead. I'm looking for a sound method of floating given the above conditions. Backer board is obviously not the answer.

    AAMOI, San Jose bldg dept were passing shower walls with drywall behind a floated coat up to 2001, as far as i recall.
  15. ballvalve

    ballvalve General Engineering Contractor

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  16. cacher_chick

    cacher_chick Test, Don't Guess!

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    Why would you NOT want to do a wet area with CBU, which IS the industry standard for tile installation, both wet and dry?

    I suspect that you should research what is common practice in tile today.
  17. rap

    rap New Member

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    Location:
    california
    ballvalve, thank you for your post.

    cacher, the Gold Standard in tile backing was and is a floated coat. It's the quickest and easiest way to plumb and square out of line studwork - provided that
    one has the relatively simple plastering skill required. The method is commonly used in the West and the Southwest: see michael byrne and johnbridge.com
    I have demo'd floated shower walls from the 1920's where the tile ( read grout ) had failed long before, and yet no moisture had penetrated the backing to damage studs or structure, and this after 80 years of wear and Ca. earth tremors.
    Going a little further afield, one might view sound, tile installations over floated backings in Rome and Istanbul that were fixed over a 1000 years ago.
  18. cacher_chick

    cacher_chick Test, Don't Guess!

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    I see a lot of lathe and horsehair plaster around here, which was the standard in it's day.

    Much like cast iron drains fitted with lead & oakum, galvanized supply pipe, drum traps, wiped lead joints, etc., etc., etc.

    I respect the old methods, but have moved on to to materials which are more user friendly.


    Going back to your original question- I don't understand why you would do a float coat over drywall, but cannot do the same thing over a CBU product?
    Last edited: Mar 24, 2012
  19. LLigetfa

    LLigetfa DIYer, not in the trades

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    Squaring out-of-line studwork with CBU can be done before hanging the CBU by shimming/planing or after by skim coating. As for "the relatively simple plastering skill required" that must be a rare commodity given all the humps and built-up corners I've had to work around.
  20. Hackney plumbing

    Hackney plumbing Homeowner

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    Alot of people dont know this but cast iron is more forgiving that plastic at the fitting connections. You can deflect cast iron lead and oakum joints I believe up to 6 degrees. In other words you can make a 45 into a 51 degree or a 39 degree bend and still have a sound joint. You cant do that with PVC.

    Sorry I knwo thats kinda off subject. LOL
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