Q. I’m installing a lot of crown molding in a finished home, and wondering whether it’s better to prepaint the crown and just touch up the nail holes, or paint it once it’s in place?

A.Robert Sanders, a restoration contractor in Pasadena, Calif., responds: Prepainting might seem like a good idea at first, but you’ll get a better job in the same or less time if you paint the crown in place. The fact is, the walls and ceiling always have some irregularities and the crown may be warped or cupped. Inevitably there will be gaps where the crown meets the walls and ceiling, and for a professional-looking job, these gaps must be caulked. The caulking, plus any spackling at nail holes and joints, must be painted. You might try cutting in just the caulk lines and touching up the spackling, but since neither latex nor alkyd enamel patches well, the areas you painted in place would likely show up.

I would prime and sand the crown, then install it. Spackle, then sand smooth all nail holes, corners, and joints. Spot-prime all spackling. Fill any gaps behind or above the crown that are larger than 1/16 inch. Caulk the entire length of the crown, at both ceiling and walls. Top coat with two coats of enamel, then cut into the crown with the appropriate ceiling or wall paint. Make sure your customer understands that all newly applied paints will not exactly match the color of the existing paints, and may visibly affect the texture of the existing walls.

By the way, whenever I install crown molding, I rip a backer out of dimensional lumber and run it around the perimeter of the room, mitering the inside corners. I then nail the crown to the backer (see illustration). Both MDF and finger-jointed pine are assured a long-lasting, trouble-free installation using this technique, and I consider it a must for any material in earthquake country. I used this method on a now 14-year-old installation that has survived two earthquakes with no more than hairline cracks at the joints.