Question:
Drywall manufacturers recommend wetting
gypsum wallboard in order to bend it for radius
walls and other curves. With all the worries
about mold, particularly with gypsum board,
this seems to be counterintuitive and, at the least, risky. I know
that it’s supposed to be fully dried before finishing, but this still
seems unorthodox. Do you know if this is still the recommended
method from manufacturers? —F.E.
Answer:
Lately it seems that every aspect of construction,
even years after the fact, has a built-in
mold time bomb attached, just waiting for
some eager lawyer to light the fuse. To tell the truth, I have heard
that because gypsum wallboard’s paper surface is both composed
of cellulose fibers and has lots of pores to offer mold
spores a nice nesting place, it can indeed support mold growth
under the right circumstances. It has also become part of the
anti-mold mantra that one must eliminate all possible avenues
or sources of moisture to ensure that the inescapable fog of mold
spores that surrounds us does not get properly watered to the
point that it can spread. Obviously adding water to such a surface
at first glance seems as smart as smoking near an oxygen
generator; on the other hand, I had not heard that the practice
had changed either.
The Gypsum Association publication GA-226-96, Application
of Gypsum Board to Form Curved Surfaces, offers both a dry
and a wet method of applying the board to curved surfaces. This
document explains that a dry board can be bent just so far, but
if wetted front and back using either a roller or sprayer, then left
flat for at least an hour, the board can be bent to an even shorter
radius.
A quick call to the Gypsum Association confirmed that this
document is still current. I was also reminded that the contractor
should provide proper drying conditions, which include
the use of dehumidifiers and fans, to ensure that the board dries
sufficiently for the job to proceed in at timely and moldfree
fashion.
Occasionally we receive a particularly interesting question on
AWCI’s NetForum, at www.awci.org/neforum/awci/a, where the
posted question is answered by several industry experts and warrants
sharing here in Wachuwannano. Here is such an exchange:
Question:
What are the considerations of applying stuc-co
over a 26 gauge thick sheet metal skin on a
steel building! That seems too light. Are there
other considerations? Should this even be attempted? —J.M.
Answer:
From Robert E. Wilson of Rinker Materials:
Twenty-six gauge is pretty much standard for
metal buildings. It should have ribs every 12
inches. I would recommend that you use 3.4 self-furring paper backed
lath with self-tapping wafer head screws and attach on
every rib (at 12-inch centers). I have used this method many
times with favorable results. Don’t forget to use control joints
every 144 square feet.
And from Kevin Day of Morrison Hershfield: Twenty-six gauge
metal is only one consideration; design deflection is another.
Anything with a wind design for less than L/360 could still
cause problems—even with adequate control joints. My main
concern stems from the fact that pre-engineered steel buildings
often have design wind load deflection much greater than
L/360 (such as L/60 or L/120: that’s 1 inch deflection over 60,
and 1 in 120 respectively—too much movement for stucco).
About the Author
Lee G. Jones is AWCI’s director of technical services. Send your
questions to him in care of AWCI’s Construction Dimensions,
or send your e-mail question to [email protected].
