Tips for Cutting and Installing Crown Molding

Determine how far out from the wall the edge of the molding will fall. Place a piece of the crown inside a framing square to find this measurement. Mark this distance on the ceiling near the corners and at several points along the length of the wall.

Starting with the wall opposite the door, cut the molding to length with square cuts on both ends. Hold it in place and nail it first to the wall studs with 8d nails, then to the ceiling joists.

If the wall runs parallel to the ceiling joists, there may be no framing members in position to nail the molding to the ceiling. In this situation, cut some triangular nailing blocks to attach to the wall studs. Size the blocks to allow a 1/4-inch gap between the block and the back of the crown.

The second piece of crown is cut square on one end and coped on the other. To cut the cope, start with an inside miter cut. Hold the crown in your miter box upside down (as if the base of the box were the ceiling and the fence were the wall) and backwards (if the cope is on the right end of the piece, the cut will be on the left as the piece rests in the miter box).

Create the cope by sawing along the intersection of the miter cut and the face of the profile. Angle the saw slightly so the joint is undercut. Test the fit against a piece of scrap molding and fine-tune the piece with a utility knife. Nail the piece in place as before. Proceed around the room, making square cuts on one end and coped cuts on the other end of each piece. Make coped cuts on both ends of the last piece.

For outside miters, the pieces also are held in the saw upside down and backwards, but the cut is angled in the opposite direction. To get a tighter fit in both outside and inside corners, flex and twist the pieces slightly before driving in the nails closest to the joint.

In the heyday of the plasterer's craft, elaborate crown moldings in fine homes often were cast in place from plaster rather than made of wood. Today, thanks to a new molding material, you can create the same effect with less skill than it takes to install wood molding. This new material has a lightweight core of expanded polystyrene -- the same material used to make a plastic foam cup. The polystyrene comes coated with gypsum plaster, so you really are getting a plaster surface.

The good news for do-it-yourselfers is that the molding is attached to the wall with any lightweight sandable joint compound. No nails are needed and joints with gaps up to 1/8 inch are easy to fill with the same joint compound used to install the molding. Also, inside miter joints are used instead of coped joints. Cut the molding with a miter box or miter saw and finish it with the same paint you use on the other trim in the room.

Cut the molding as you would wood molding, except make miter cuts instead of copes for inside corners. Use a putty knife to apply a 3/8-inch-wide swath of sandable joint compound to the top and bottom edges of the crown.

Press the molding into place, causing the joint compound to ooze out along the length. Where the molding meets the ceiling and wall, smooth the excess with your finger.

To join two pieces in a straight run, use a butt joint. Wherever one piece of molding joins another, coat the adjoining face of the second piece with joint compound before you press it into place. Use a damp sponge to wipe off any excess that squeezes out.

After the adhesive dries, smooth joints with a fine-grit sanding sponge, which will conform to the shape of the molding. Dab in joint compound to fill any gaps. Sand again as needed.

You may need to end a run of crown molding without turning a corner or stopping at a wall. If so, stop the molding with a triangular return piece. To cut this piece, place a scrap of crown upside down in the chop saw or miter box and make an inside miter cut. Then set the saw to 90 degrees, align the blade to the point where the miter ends at the back of the molding, and cut off the triangle. Attach the return piece with yellow carpenter's glue. Use masking tape to hold the piece in place until the glue sets.