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Thread: green board in ceiling???

  1. #1
    DIY Senior Member coach606's Avatar
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    Default green board in ceiling???

    My drywall company installed green board in my new bathroom ceiling. I've got a showerhead in the ceiling and it won't be tiled.

    My contractor insists that greenboard should not be installed in a ceiling because it will sag.

    Has anyone heard of that before? Is it really a problem?

    Thanks.

  2. #2
    In the Trades Gary Swart's Avatar
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    Default

    I don't know why greenboard would sag when regular drywall won't. Perhaps this is the one thing in the world I don't know, so better check with a drywall pro just to make sure.

  3. #3

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    The only difference between greenboard and regular sheetrock is the paper covering. The greenboard might be a bit tougher to prime and paint, but sag???

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Yes, greenboard is spec'ed for 12" supports when used on a ceiling...normal drywall 16". It is NOT as strong as normal drywall, and under some circumstances can and will sag if not supported as the spec calls for. Also, normal drywall has a grain to it...it is much stronger along its length than across the panel. Not sure about greenboard. Drywall should be installed like plywood for a subfloor - across the supports, not aligned with it for maximum strength.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5

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    Two years ago I remodled my 7 x 10 bathroom in my circa 1933 house with Greenboard. As JD rightly pointed out, I installed it across the joists. All of my former wire lath/plaster ceiling joists were spaced somewhat less than 16"; average 14." I used Greenboard before I knew that the gypsum is mixed with (if I remember correctly) a petroleum additive to limit moisture issues. After I installed the Greenboard, but before I mudded and taped, I learned about the 12" OC recommendations. I went back and added some more screws just for kicks. I thought about sistering the joists from the attic, but I said "nah." Anyhow, after two years I don't see a bit of sag in the ceiling. Maybe I was lucky; maybe the sags won't show up (like people) until a few more years; maybe the standard is too strict. I don't know, but Greenboard worked for me.

  6. #6
    Homeowner geniescience's Avatar
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    Default Only so-so, not great.

    coach

    First, about the plaster component. FAIK, and I heard this from someone who worked a long time inside the factory, there is an additive in the gypsum mix in Greenboard, and that is the only difference in the plaster part of the product. It helps keep it rigid longer when damp, wet or waterlogged, before it ultimately falls aprat liek regular plasterboard sheetrock. They all lose rigidity and start disintegrating (falling apart) underneath the paper coating at some level of moisture and aging. The missing factor in your case here is how much the average permanent humidity is or will be in your shower. Not the peak 15 minute spike during and after a shower, but the real amount of long-term moisture in your environment. Not to worry. I don't predict any problem.

    Second, about the paper facing. The product still has a problem, and the manufacturer knows all about it, and they have already started making another ("better") water-resistant board, that claims to be able to resist mold colony growth better. Moisture enables mold to start eating (ie. rotting) the paper, inside walls and ceilings, on the back side where you'll never see it.

    The fact that Greenboard is more rigid when damp is not a plus when its bigger problem isn't solved, i.e. letting mold grow. All it is, is a big sponge that remains rigid longer than the low-grade product.

    Whether it is screwed at 12" or 14" o.c. is not a big issue in the first few years. When it will sag depends more on the average permanent humidity in your environment (home), and 14" apart support is just 15% less mechanical support than the recommended amount.

    David

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