Should I even bother putting this drywall up?

Discussion in 'Remodel Forum & Blog' started by amateurplumber1, Aug 20, 2014.

  1. amateurplumber1

    amateurplumber1 Member

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    I originally had this piece of drywall as two pieces, and quickly learned that I couldnt do the whole section at once. But apparently not before a corner got snagged against something and broke. Can I fix this corner, or should I not even bother putting it up? It will go behind kerdi membrane and drywall. This may seem like a stupid question but I've never done drywall before.

    Thanks!
    Last edited: Aug 20, 2014
  2. johnfrwhipple

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

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    North Vancouver, BC
    Well if you are planning on using Kerdi over the drywall then you best make sure you do not make the slightest of mistakes. Drywall is a horrible choice as a tile backer board - even if covered with Kerdi.

    If you must use drywall at least switch out your waterproofing to something like Ardex 8+9. I stopped using Schluter's products - they make the Kerdi you are planning on using. The products are cheap and thin. Great if your packing containers for shipping. Not the best in my opinion if your building a waterproof shower.

    The corner you nicked is a nothing repair. Remember if you use Kerdi make sure to use cheap un modified thin-set. Both below and above the membrane. Schluter does not want any modified setting materials on their jobs. Modified thin-sets seem to work better. Have more flexibility. Offer up better holding power. Things like that.

    But non-modified thin-set when mixed perfectly and installed flawlessly are fine too - or so Jim likes to tell us.

    The best backer board behind any waterproofing right now sold in North America is WonderBoard Lite. You should leave some concrete board and drywall outside for a few weeks. Which one do you think will mold and decompose first.....


    think

    think

    the one with paper on the back side. Paper on the front side. The one that can not be taken to the regular land fill. The one with the largest contributor to our land fills. What do they call it..... hmmmm

    DRYWALL
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    You might want to view this test report from the Gypsum Association about the shear strength of gypsum board http://www.grabberman.eu/Media/TechnicalData/450.pdf . You will get a very significant difference in shear strength based on your screw spacing. But, consider that the specs for all bonded membranes to whatever substrate you choose is that it must be over 50psi (and Kerdi generally tests out upwards of 75psi). So, the thing you should take away from this is that the bond strength of the fleece on a bonded membrane, I don't care whose you choose, will be less than the strength of the substrate, drywall included, by a factor of at least 2, and under ideal conditions, over 8 if you choose the smaller spacing used in the testing.

    A double margin of safety is plenty. An eight-fold one is way overkill, but easy to attain, if that floats your boat. The fact that two significant companies in the industry allow their membranes to be installed over drywall, and one that has been doing it for over 25-years with success in a shower (Schluter's Kerdi and Laticrete's Hydroban membrane - Kerdi is by far the older one) would seem to make John's argument kind of misguided. If you install the membrane properly, it passes all of the A118.10 tests and has been certified by independent testing to provide a totally waterproof shower. What more do you want?

    Thin has it's advantages - all corners done with a bonded membrane will end up with 3-layers on part of it. John's preferred one is 3.5x thicker than Kerdi. That Noble membrane will end up being 90-mils + two layers of sealant thick or about 1/8" bump in the corner. The Kerdi corner will end up about 24-mils plus two layers of thinset, about 1/4 of the overall thickness. Given the TCNA guideline of no more than 1/8" in one foot out of plane for a smaller tile, and 1/16" for a big one, guess what...the simple, required act of making a waterproof corner puts the surface out of tolerance with the Noble membrane. Should you need greater perm rating for a steam shower, Noble will give it to you, but so will the thicker version of Kerdi (KerdiDS), and it will still be a lot thinner.

    Just goes to show how far John will go to trash a company. If you really want to, both Schluter and Laticrete have tested their membranes for use over lots of other surfaces, including a cbu, so you can use of the others (including cbu) if that makes you feel better.
  4. amateurplumber1

    amateurplumber1 Member

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    Do I have to fill in that corner or anything to solidify it?
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    Put a little dab of thinset between the flap of the pieces on that crack, push it back together, and carry on. You want it flat, but unless you're using a small mosaic, it won't hurt anything once you've got the membrane over it and tile. You could cut out the corner, install some cleats behind it, and inset a patch, but it's not a big deal since it's so small.
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