Patching and sanding Sheetrock (commonly referred to as drywall) before painting it ensures a smooth surface and a uniform sheen. If the drywall is older and has been dented or banged up, you'll probably need to do some drywall repair and then prime the entire surface. It's tempting just to slap on a couple of coats of paint, but paint won't hide many flaws. Proper surface preparation is an essential part of any painting project.
Dust off the Sheetrock and inspect it in good lighting. Shallow dents, scratches and small nail holes will be very apparent when the Sheetrock is painted. Use Spackle for small repairs and joint compound for larger ones, extending the patching compound several inches past the repair so you can sand it flush with the surface. Older unpainted Sheetrock may have loosened tape joints. Use a utility knife to remove loose or wrinkled tape and replace it with fresh tape, then cover it with two or three coats of drywall mud. Caulk any cracks and gaps between trim and the wall, or along corners, with paintable caulking. Don't assume paint will "fill in" even hairline cracks---it won't.
Use a drywall mesh sander instead of a block of sandpaper. It doesn't clog up with the powdery sanding dust as quickly, and the large pad allows you to sand the Sheetrock quickly and evenly. Before you start, lay towels over wall and floor vents, or tape plastic over them, to prevent dust from getting into your duct work. Sanding Sheetrock can be messy. Look for "no dust" joint compound at paint and hardware stores. Instead of floating through the air and coating your entire house, the dust is formulated to fall straight to the ground, where it can be easily swept or vacuumed up.
Unpainted Sheetrock should be completely primed. If it's already painted and in reasonably good condition, just prime the patched areas. Use a general-purpose water-based latex primer, or PVA drywall primer. If you are particular, check the Sheetrock for imperfections once the primer is dry. It's much easier to see scratches and dents you missed or didn't repair perfectly once the primer has been applied.
Older Sheetrock may have water damage and tannin staining, or dirt that will bleed through water-based primer and paint. If the Sheetrock is very dirty or has brown stains, use a stain-blocking shellac- or oil-based primer.
Keep in mind that the shinier the paint, the more it will accentuate surface irregularities. Some paint companies sell washable flat or "matte" paint that has an extremely low luster but can be washed without leaving smears or marks on the wall.
- Photo Credit drywall tools image by Sherri Camp from Fotolia.com
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