Building Custom Crown Molding
Also see:This page contains instructions for installing custom–built crown molding. The diagram below offers one idea for creating an elaborate crown molding profile using these commonly available trim molding pieces, finished lumber and one of these one–piece crown molding profiles.
Combination Crown Molding Diagram
The components that makeup the custom–built crown molding in this diagram include: A–a one–piece crown molding profile, B and C–small accent moldings like base cap and back band, D–square moldings like brick mold to add some dimension and E–the backer boards that serve as a foundation for most custom crown molding. These can be one–piece baseboard and case moldings or may be built using finish lumber and small accent moldings to finish the edge. The backer boards will significantly widen the molding and may not be appropriate along the top edge of a custom crown molding on lower ceilings (less than 8 feet).
Mark Walls and Ceiling
Before beginning locate the studs and joists so that the molding can be nailed to the framing.
Measure down from the ceiling and mark the wall over the studs where the top of piece E should fall. For the diagram above that would be 2-5/8 inches.
Next measure out from the walls and mark the ceiling for any backer board there. For this project the measurement is 1-3/4 inches.
Install the Backer Boards
Join the square backer boards in this project using an overlapping butt joint on inside corners and 45° miters on outside corners. If you're using a shaped baseboard or other one–piece molding as a backer board, cut and joint it using miter joints at all ceiling corners and outside wall corners. Inside wall corners can be coped or joined with a 45° miter.
Use 2½ inches or 8d finishing nails to attach the backer boards to the wall and ceiling framing. Drive the nails at the studs and joists and sink the heads to just below the surface of the wood trim. Using a pneumatic nail gun will set the nails automatically and will make installing this and other trim moldings much easier.
Install the Dimension Molding
Measure from the inner edge on the backer board and mark the position of the square piece of dimension molding. For this project that would be 1 inch.
Cut the molding square and over lap the ends as with the backer board installation. Caulk the edge where it contacts the backer and nail the molding in place using 2 or 2½ inch nails. Clean off any excess caulk that oozes out with a clean wet rag.
Install the Crown Molding
Cut the crown molding using either the coping or compound miter methods. If you feel comfortable coping a molding joint, that can be the easier way to get a seamless fit.
Apply a bead of caulk along each edge of the molding and nail it in place at the top and bottom with finishing nails about 1½inches long. Space the nails every 18 to 24 inches and sink the heads just below the surface of the moldings. Wipe off any oozing caulk with a clean, wet rag before it can set.
Install the Accent Moldings
Cut the accent moldings to fit along the outer edge and at the joints between the dimension moldings and backer boards.
45° miters can be used to joint the corners of these small moldings. Or the moldings on the wall may also be joined using a coped joint at the inside corners.
