By Winston Montgomery

Some folks think there's not much to interior painting. "Just buy a brush and paint everything white," they say. Or, "Choose warm colors and get creative." But hold on, Picasso! The real artistry—and effort—in a professional-quality paint job is in the prep work. Here are some tips and trade secrets the pros use to ensure a great job. You can use these same techniques yourself.

A note about lead-based paint: If your home was built before 1978, the paint used on it may contain lead. You may want to have a sample tested by a laboratory. If the lead levels are high, don't scrape or sand it yourself. You may release contaminated chips and dust into the air. You're better off hiring experienced professionals—who have the necessary safety equipment and know what precautions to take.

Step by Step

1. Prep for the prep. Take down drapes, curtains, blinds, pictures and shelves. Remove whatever furniture you can and push the rest to the middle of the room, leaving at least 3 feet of clear working space on all sides. Cover your central pile of furniture and furnishings with inexpensive plastic drop cloths. Remove switch and outlet plates, picture hooks and other hardware. (You can leave mounting brackets for shelves and curtain rods shelves in place, but protect them with masking tape.) Cover the floor with cloth drop cloths. They may seem expensive, but they aren't slippery underfoot like plastic, they absorb minor spills—and you can reuse them. Finally, make sure that you'll have plenty of strong light to paint by.

2. Wash it down. High-traffic areas like kitchens and baths should be washed with a solution of TSP and water to remove grease, soap and other filmy deposits. If you find mildew, add bleach to the cleaning solution. Rinse every surface after you wash it, and be sure everything's thoroughly dry before you go any further.

Safety: Wear rubber gloves and goggles when you're using bleach, especially when you wash overhead surfaces.

3. Scrape off loose paint. Carefully go over painted wood trim, doors and windows. If you find loose, blistered or peeling paint, use a scraper to get it off. Don't gouge into the wood, though; the goal is not to remove all the paint—just the stuff that's clearly not attached well.

The best pull-type scrapers have replaceable carbide blades (which stay sharp far longer than steel) and large comfortable handles. Use one about 3 inches across for plain surfaces, and a molding scraper for curved or fancy trim. Windows usually need the most preparation.

4. Sand off the gloss and feather the edges. Walls and ceilings painted with flat paint generally don't need to be sanded. But trim, especially around windows and doors, is usually painted with at least semigloss paint because it's easier to clean and harder to mar. The same goes for walls and ceilings in kitchens and bathrooms. You'll need to sand any glossy surface to give it a good "tooth" for new paint to adhere to. A light sanding with 120-grit sandpaper should do— unless you plan to put latex over oil-based paint. Wearing gloves and a dust mask is a good idea.

If you're putting latex over an oil-based paint, sand thoroughly. Use medium (80-grit) sandpaper, and be sure to feather the edges of chipped paint down to the adjacent wood. You'll know you're sanding latex paint if it's hard to feather and it gums up the sandpaper. Do the best you can: change paper often or try a coarser grit.

Use a half-sheet hand sander or a pole sander for more reach and leverage. For tight spaces, try folding up a piece of sandpaper and using just the edges to sand in grooves and corners.

Concentrate on removing flaws like drips, sags and built-up paint on edges and corners. With latex paint it's often easier to slice away most of a drip with a razor knife or utility knife and then sand. But use a light hand—you don't want to take a slice out of the molding.

Power sanders can make your work easier, but be sure to wear a dust mask when you use them. A random-orbit sander works best for wide, flat surfaces, and a finish sander is good for contoured molding and trim.

If too many coats of old paint obscure the shape of the trim, consider completely removing the paint with a heat gun or a chemical stripper. Follow the directions that come with these products carefully. You'll need putty knives and scrapers for this job; you may want to set aside a few just for stripping.

5. Prime as necessary. Priming is important, on inside as well as outside surfaces. Primer isn't like regular paint; it's formulated to seal the surface it's applied to and bond to the topcoat. If the paint you're going over is in very good condition or is the same type as the new paint—oil or latex—you don't have to prime. But it ensures a more uniform topcoat, especially if you're going from a flat finish to gloss or semigloss. You can brush it on or use a roller.

If you'll be putting latex paint over gloss or semigloss oil-based paint, use an oil-based primer. Always prime any porous surface, especially the following: new patches in drywall and plaster; newly installed wood and newly exposed wood; dark colors, if you intend to cover them with light ones; and stained areas (use a stain-blocking primer).

You can paint over wallpaper, but seal it first with an oil-based primer. If the wallpaper is torn or peeling, though, you should probably remove it before you prime. Liquid wallpaper remover and scrapers are your tools, but scrape gently or you'll have a lot of patching to do after you prime.

6. Patch and caulk. Check walls and ceilings for "nail pops" and dents in drywall; there may also be holes from picture hooks that need to be filled. Fill nail holes and shallow craters on trim, doors and windows with patching compound or spackling paste. Use a putty knife or, for small holes, your fingers. Vinyl and resin-based compounds are the easiest to work with, though they shrink as they dry. Overfill the holes and then sand them smooth and even with the surface.

A fast-curing compound or plaster can help fill big, deep holes on walls and ceilings, but it's hard to sand. This material makes a fine "base coat" in a deep hole, but you'll want to finish the surface with a patching compound. You can use this combination to patch smaller holes (under 1/2 inch) in walls and ceilings, too.

Tip From the Pros

Never use pure silicone caulk when you prep. It won't bond with paint.

Look carefully for cracks, seams, open joints in trim, and gaps between moldings and wall surfaces. Use an acrylic latex caulk and a caulking gun to fill these.

Some caulk shrinks as it dries, and you may need two applications in wider spots. Shoot plenty of caulk into the gap, then push it in and smooth it with your moistened finger. If the gap is bigger than 3/8 inch, stuff in foam backer rod before you caulk, so you can use less. (Backer rod isn't a rod but rather a ropelike length of foam used to fill long cracks.)

Once everything's sealed up tight, break out the brushes. You're ready to paint your masterpiece.

Winston Montgomery has been a painting and drywall contractor in the San Francisco Bay Area for over 25 years.