Q&A: Can I cover up oil paint with a water-based latex?

A: You can apply water-based latex paints over interior or exterior oil-based paints and even stains, says Rico De Paz, who oversees paint and stain testing at Consumer Reports. But for best results, use a top-ranking paint from Consumer Reports' tests. And unless you're using a Behr primerless paint, also use the specific primer suggested by the paint manufacturer.

"If you need to scrape or sand the old oil paint, be sure it wasn't applied before 1978," De Paz noted. "If that's the case, there's a good chance the paint contains lead, and you must by law use an EPA-certified contractor. You can save by having the contractor do the sanding, prep work, and priming, then do the finish coats yourself. But you don't want to be stirring up any hazardous lead dust."

Some more ways to get the best possible results using water-based latex paints:

• Clean the surface well; use a pressure washer on outdoor surfaces.
• Use a synthetic-bristle brush for latex paint with a feathered or tapered tip. That makes it easier to apply paint to the brush.
• Avoid cheap brushes; a quality brush will give you a much better finish.
• Soak the brush in water for an hour before using it. That helps the bristles pick up the paint better.
• Don't spread paint too thin; try to cover a 1-foot section of 8-inch-high siding with each dip of the paintbrush.
• If you miss a spot, don't go back and touch it up. The bare or thin spot will be drier than the surrounding paint, and trying to even it out is likely to mar the wet paint around the spot. Instead, wait four hours (the usual drying time for a coat of water-based latex paint) and then touch it up.

More on paints and stains: See our free buying guides to paints and wood stains. Full Ratings are available to subscribers.

—Gian Trotta