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Q.Can you skim-coat plaster over regular drywall? If not, is there a way to prep standard drywall so that a veneer plaster finish can be applied over it?

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.