Of all the different types of interior trim found in a home, none attracts more attention than crown molding. Perched high overhead at the junction between the wall and ceiling, crown molding adds elegance and architectural interest to any room. And unlike most trim, crown molding can actually increase the value of your home.
Installing crown is a bit trickier than other trim because it requires cutting compound angles, but don’t let that frighten you. Here’s a straightforward step-by-step approach—accompanied by a few tricks of the trade—to help even novice DIYers put up crown molding like a pro. However, before describing how to cut crown, let’s talk briefly about prep work and the tools you’ll need.
Crown molding is typically nailed to the wall studs and to the ceiling joists. The problem is that joists only run in one direction above the ceiling, leaving no joists to nail into along two of the walls.
Now if the crown is small enough, say about 1½ to 3 inches wide, you can usually get a tight fit against the ceiling by only nailing into the wall studs. However, for larger crown I recommend installing a plywood backer board, which provides a solid nailing surface at any point along every wall.
To determine the width of the backer board, lay a framing square onto a sheet of paper. Hold a short piece of crown molding against the inside corner of the square. Draw a line along the back of the crown. Measure the length of the diagonal line, then subtract 1/8 in. for clearance. That dimension is the width of the backer board.
Tilt a table saw blade to 45°, adjust the rip fence to the proper width of cut, then bevel-rip the backer board from ¾-inch plywood. Rotate the backer board end-for-end and bevel-rip the opposite edge. Now fasten the backer board at an angle between the wall and ceiling using 3-in. drywall screws. Again, the advantage of the backer board is that you can now nail the crown at any point along its length.
And while we’re discussing nailing up crown molding, it’s worth mentioning that a pneumatic finishing nailer provides the quickest, easiest way to install crown. If you decide to hand-nail the crown, that’s fine, just be sure to bore pilot holes when nailing near the end of the molding. Otherwise, the molding will crack.
Save yourself tons of time and trouble by applying a finish to the crown molding before you install it. Applying primer and paint, or stain and varnish are much easier and neater when the molding is laying across sawhorses (check out the JawStand XP), than when it’s already nailed in place at the top of the wall.
And note that many styles of paint-grade crown moldings come factory-primed and ready for paint.
There are two basic ways to cut crown, and both require a power miter saw. Some people find it easier to cut crown molding using a compound miter saw because you can hold the molding flat against the saw table.
However, that requires adjusting the saw blade to make both a bevel cut and miter cut at very exact angles, and those precise angles differ depending on the size of the crown.
Most DIYers find it easier to set the molding against the saw at the same angle that it’ll be installed against the wall and ceiling. That way, regardless of the size of the crown, all cuts are made with the saw adjusted for a simple 45° miter cut. Just remember that when using this method, you must set the crown molding upside down with its upper edge against the saw’s table, and its bottom edge resting against the vertical saw fence.
Most crown molding comes in 16-foot lengths, so unless you’re trimming out a gymnasium, you can usually span each wall with a single piece of crown. However, it’s still important to know how to join together two lengths of crown end to end with a scarf joint.
A scarf joint is simply two opposing compound-angle miter joints that meet to create a clean, nearly undetectable seam. The reason scarf joints are preferred over simple butt joints is that if the molding should shrink or shift out of position slightly, a gap won’t appear at the seam.
To form a scarf joint, first execute a compound-angle miter cut on the end of one length of crown. Nail the crown to the backer board and then make an opposing compound-angle miter cut onto the end of the mating length of crown. Apply some wood glue to the joint, then slide the second piece of crown into position and nailed it to the backer board.
Inside-Corner Coped Joints
A coped joint is used to join together two pieces of crown molding at an inside room corner. This type of joint is preferred over a miter joint because wall corners are rarely perfectly square (90°) and a coped joint creates a tight-fitting seam regardless of the corner angle.
It’s much harder to explain how to cut a coped joint than it is to actually cut one, but here goes:
Square-cut the first length of crown molding, push it tight into the corner and nail it in place. Cut a compound-angle miter onto the end of the mating length of crown. Then use a coping saw to back-cut the molding along its contoured profile. The idea is to saw away enough wood to allow the coped cut to fit snugly against the profile of the square-end piece of crown.
However, the coped piece will need a little fine-tuning before it fits snugly. Smooth the coped joint with a wood dowel wrapped in 80-grit sandpaper and with various files, including rat-tail, half-round and flat files. It’ll take a little patience and practice, but before long you’ll be able to create tight-fitting coped joints in a matter of minutes.
Outside-Corner Miter Joints
Not every room has outside wall corners, but if yours does, you’ll need to execute a compound-angle miter joint to join together two lengths of crown molding.
However, since outside wall corners are seldom perfectly square, you can’t simply cut both crown pieces to 45° and expect them to meet snugly at the corner. Here’s a technique that I’ve used for years to cut perfect outside miter joints, regardless of the wall angle:
Start by holding two 20-inch-long 1x4s against the ceiling at an outside corner, allowing them to overlap by a few inches. Trace a line along both edges of the lower board to mark the upper board.
Next, draw a diagonal line connecting the two straight lines. Then stack the 1x4s on the miter saw table, adjust the saw-blade angle to match the diagonal line, and cut both 1x4s.
Test-fit the 1x4s by holding them against the outside corner and checking the miter joint. If it isn’t tight, adjust the blade angle and make a second cut. Once satisfied with the fit of the 1x4s, lock the blade angle in place and make a compound-angle cut into one of the lengths of crown. Adjust the saw to make an opposing miter cut—at the same exact angle—into the end of the mating piece of crown.
Nail the piece first of crown to the backer board with its end flush with the wall corner. Next, smear wood glue onto the joint, slide the mating piece of crown into place and nail it to the backer board.
If the corner joint isn’t tight, don’t nail it using a pneumatic nailer. It’s too risky; the nails could easily deflect and break through the face of the molding. Instead, hand-nail the miter joint with 1½-inch (4d) finishing nails. Be sure to drill pilot-holes first to prevent splitting. Wait for the glue to dry, then lightly sand the miter joint with 100-grit sandpaper.