A.Robin Raymer of
Plasterzone.com, an author, educator, and veteran
plastering contractor, responds: Plaster-base
gypsum board — or blue board — is
designed for veneer-coat plaster. It has an
absorbent paper face that draws moisture out of the
plaster as it sets. The paper chemically reacts to
the plaster applied over it, strengthening the bond
between the plaster and the blue board.
Regular gypsum board — drywall
— has the same core, but the paper face is
slicker and less absorbent so that moisture in the
joint compound dries to the air rather than being
absorbed by the board. Regular gypsum board is
sometimes hung with the back facing out in the
mistaken belief that this gives the board more
suction and gripping power for the plaster.
Like many other plastering contractors, I'm
often called in to do one- or two-coat veneer
plastering where drywall has been hung instead of
blue board. In such cases, some contractors will
first apply a latex bonding agent to the drywall
(regardless of whether it's been reversed), but
I've had good success just plastering right over
the drywall. I've compared notes with other
contractors about literally hundreds of thousands
of board feet of plaster applied over both blue
board and drywall, and have discovered that in
practice there's very little difference in how blue
board and drywall react to the plaster.
However, since drywall tends to absorb less
moisture, I've found that the texture stays wet
longer when I base-coat and do sand-finish
texturing the same day. So I add an accelerator to
the texture to help it stiffen, which allows me to
finish it out faster.
Otherwise, your primary concern should be that
the boards are properly hung. Broken boards and
gaps always present a challenge, whether the finish
is joint compound or plaster.