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

  1. #16
    Test, Don't Guess! cacher_chick's Avatar
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    Quote Originally Posted by tom12 View Post
    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.

    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.

  2. #17
    DIY Member tom12's Avatar
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    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.

  3. #18
    Test, Don't Guess! cacher_chick's Avatar
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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 by cacher_chick; 03-24-2012 at 07:56 AM.

  4. #19
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by tom12 View Post
    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.
    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.

  5. #20
    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

  6. #21
    Retired Defense Industry Engineer jadnashua's Avatar
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    A floated wall is the cadilac of walls, just like a mudbed is for flattening a floor prior to tiling. Now, the way it is actually put together can produce something to be proud of, or a piece of junk, depending on how well it is executed for both the car and the wall!
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #22
    DIY Member tom12's Avatar
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    LLgetfa, thank you for your reply,
    Obviously, squaring up of CBU can be done by shimming etc, but thats not the point in contention. FWIW: the guys who taught me would one-coat a three wall tub surround - using sticks/screeds - in approx 40 mins. Flat, plumb, square to a perfectly controlled depth.
    I dont understand your difficulties with "humps" etc? Assuming that you have basic plastering skills, then floating sand and cement and lime is the most basic form of skill required. It will pull-out all uneven background. Inside corners are rubbed and cut-in to square with a plastic or wood float.

    cacher, thank you for your post,
    Point is, that floating has not had it's day, it's still widely used, for example, a large, SF Bay Area tile co. that i know of, floated all it's walls and screeded all it's floors and counter tops, no CBU. $10k to $80k jobs.
    A long term, secure, mechanical fixing for the wire or mesh is necessary for floating.
    What method would you propose for fixing metal to CBU?

  8. #23
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by tom12 View Post
    I dont understand your difficulties with "humps" etc?
    The difficulty is not with my ability to not make humps, it is that the humps are already there when I go to tile, hang cabinets, lay countertops, etc..

  9. #24
    Test, Don't Guess! cacher_chick's Avatar
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    I have no experience with floating walls, but I know that it has become pretty common to install masonry veneer over CBU. When doing this, the lath or wire is installed with corrosion-resistant screws through the CBU to the studs.

    Whatever you end up doing, post some pictures along the way- we would all enjoy seeing the process.

  10. #25
    DIY Member tom12's Avatar
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    LLitgetfa, Things are getting a little confused.
    1. I'm not suggesting that you are creating difficulties for yourself.
    2. A floated bed, vertical or flat, will quickly iron out all the above,existing difficulties.
    3. Perhaps as suggested by "cacher" pics would help if one is not familiar with the process. Unfortunately, among my many faults is computer illiteracy - i'm working on it. There are, however, many pics and diagrams of the process on the web - see above.

    cacher, difficulties occur in your post:
    1. Using CBU and a floating coat is time consuming and more expensive. Definitely a non-starter, especially on tracts, where production speed is the essence.
    2. Exterior fabric backing and interior wet areas are two different animals.
    3 Suppose that i used your suggestion, how many penetrations of the CBU and vapor barrier would take place in a shower or steam room? And at 16"c/c, whereas wire to drywall is stapled on at 4"c/c.
    4. I'm not asking for advice for a particular project, i'm looking for suggestions to my original post.
    5. However, thank you for your contributions.

  11. #26
    DIY Member tom12's Avatar
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    Hackney, thank you for that information ref. CI joints. It had certainly never occurred to me before, and i've been a helper around quite a few of poured joints.

  12. #27
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by tom12 View Post
    Assuming that you have basic plastering skills, then floating sand and cement and lime is the most basic form of skill required.
    You grossly underestimate the potential for poor workmanship. I contend that "the most basic form of skill" is in short supply as is "common sense" which really is not all that common.

    Yes, I could grind down a hump or even grind down the backside of a stone to clear the hump. I could also refloat the whole area if not constrained by overal thickness. I could vary the thickness of the setting mortar to even out the variation if the overall thickness allowed for it. If the designer did not make allowance for corrections, it makes more work for the setter.

    I'm not sure where this is heading. My point was that the installer of CBU should not compound the problem with tolerance stacking. If the wall is true and the corners square before install, skill level (or lack of) should not be a factor except for allowing for the corners. Of course, if the framer left bows and out-of-square corners, the CBU will simply telegraph them without additional stacking.

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