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Q.The last time I was asked to remove wallpaper and repaint the wall, much of the paper facing on the sheetrock underneath came off, too, resulting in a lot of extra wall prep. What caused this, and what's the best way to prepare drywall for a wallcovering?

A.Tish Iorio, a member of the National Guild of Professional Paperhangers and owner of Creative Endeavors in Annapolis, Md., responds: Drywall has a paper face, so wallcovering pastes adhere to it just as well as they do to wallpaper. Unless drywall has been properly primed, wallpaper paste doesn't have the ability to release from it when it is rewetted, resulting in the damage you describe.

Designed to be nonrewettable, wallcovering primers contain acrylic polymers that provide a barrier between the paste and the paper face while at the same time promoting adhesion of the wallcovering to the wall. They are more expensive than regular paint primers, which are designed mainly to provide a uniform wall color (usually white) that won't influence the color of the top coats. All of the major paint companies offer wallcovering primers, but I use Wallpaper Prep-Coat (Swing Paints, 323/816-3041, www.swingpaints.com). I like it because it's slightly green and turns gray when it comes into contact with drywall compound that hasn't been painted, making it easy to see where I need to apply a second coat. It also has diatomaceous earth in it, which leaves a "tooth" on the wall that aids adhesion.

A wallcovering primer should always be used before applying any type of wallcovering. It can go over bare drywall, primer, or existing painted surfaces.

By the way, sizing (a diluted paste) is not a good substitute for a wallcovering primer.

Consolidating products such as Gardz (Zinsser Co., 732/469-8100, www.zinsser.com) have been developed to help repair damaged drywall. Because they bind both paper and paint layers together into an impermeable surface, I use one of them whenever a damaged wall surface has been skimmed with compound or when a paint finish seems unstable. But because they are very hard, they don't give paste anything to grip, so I always use a wallcovering primer over them before I hang.