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mike
 
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In article
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mike wrote:

So... why will green drywall sag more than regular?


After posting, I found a reference to the fact that the "green" drywall
core is indeed treated to be water resistant (as opposed to my previous
reading which stated that just the paper was resistant).

I now have this explanation:

"For ceiling applications, green board requires extra support.
According to Gypsum Association guidelines, green board in a ceiling
application needs 12" o.c. support.
If supports are 16" o.c., 5/8" green board should be used. Why is this
additional support needed? Moisture repellents, such as the asphalt and
wax emulsions in the green board core formulation, act as lubricants.
These lubricants cause the gypsum crystals to slip easily, resulting in
board sag
For bathroom ceiling applications, we recommend regular or Type X
board. Simply apply a good quality sealer and two coats of latex based
paint after installation."

So to redirect the thread: would anyone with experience care to give
their opinion on the suitability or necessity of green board on a
ceiling?

Thanks,
*moc