Skimmed walls are made by applying one or more coats of drywall compound to an interior wall's surface with hand trowels. Skimming is an option for renewing the look of block, brick and other masonry walls. Painting a skimmed wall isn't difficult, but you'll need to add an additional sealing step before applying the finish paint.
Put protective paint tape on wood trim, on baseboard and over outlets and switch covers to protect these items from paint.
Apply a coat of interior sealing primer on skimmed walls. Since skimming often covers old masonry, rusty stains and moisture can travel through the skim coat and appear on a finished wall if not sealed. Roll the sealing primer on with a medium-nap roller in an even coat. Roll two coats of primer if the stains are very noticeable.
Roll a coat of paint on the wall after the sealing primer is completely dry. Roll as close as possible to the ceiling without bumping it. Paint by hand along the ceiling and around woodwork and baseboards with a high-quality paintbrush.
Repeat with at least one more coat of paint after the first coat dries. Depending upon the brand of paint you choose, a third coat may be necessary for an even finish.
Cut the protective tape with a razor knife between the painted wall and the tape. If you just pull the tape off, some of the dried wall paint may come off with it.
Drying time for primer or paint on a skimmed wall may be substantially less than it would be on a drywall surface, because the porous compound used to skim the wall absorbs moisture. Repair gouges, holes and cracks on the skimmed wall before painting. Fill nail holes with latex caulk and sand the wall surface before rolling on the sealing primer. Use drywall compound for larger cracks, spreading it into the cracks with a wide putty knife and sanding before painting. If you find it difficult to paint a straight line by hand, look for an edge-painting pad at your hardware store. These pads do not offer the same quality as a brush, but they are an option if painting by hand is difficult.
Open a window to provide ventilation and fresh air when applying primer and paint. Wear old clothing when painting. Don't tape off a painted or textured ceiling. The tape can pull off paint or plaster.