Pro Tips For Installing Crown Molding
Crown molding is not easy to install, but the right trim can transform a room. Here are illustrated step-by-step guidelines that prove that a skillful layout and smart shortcuts can change any apprentice carpenter into a ceiling molding master.
 The first time I installed crown molding, I probably wasn't really installing it at all—I was just handing my dad tools off the truck. Crown can go in any space, from the kitchen to the den, and of all the interior trim found in a home, none attracts more attention. A room with crown perched high at the wall and ceiling junction has an eye-catching focal point that a savvy Realtor will point out along with granite counters and marble baths.
This job's 4½-inch crown came from a local lumberyard—still the best place for a wide-profile selection. I splurged on clear pine at $2.70 a linear foot. If I intended to paint the crown, I could have gotten preprimed finger-jointed pine for $1.60—and I'd be able to caulk over stray gaps before painting.
Installing crown is a bit trickier than other trim because it requires cutting compound angles. Plus, out-of-square corners and bulging, wavy walls can be a nightmare for a novice. But over the course of a dozen jobs, I've come up with a few shortcuts—I don't really remember where I learned a lot of these tricks, I just know them.
Site Prep
Crown molding is usually nailed to the wall studs along the bottom edge and into the ceiling joists above—a lot of stud-finder work. I skip all that by installing a plywood backer board to the top plate (the horizontal framing member above the wall studs). That method allowed me to nail this project's 4½-inch crown to any point along every wall.
To determine the width of the backer board, I held a piece of crown molding against the inside corner of a framing square and drew a line along the crown's back (1) The diagonal line, minus 1/8-inch for clearance, is the width of the backer board. I used a table saw with the blade set to 45 degrees to rip the backer boards from 3/4-inch plywood, then fastened each board to the top plate with 3-inch drywall screws spaced 16 to 24 inches apart.
Saw Shortcut
The power miter saw and stand provide a safe, quick and accurate way to execute precise cuts. Choose a 10- or 12-inch saw with a dust-collection bag or exhaust port for attaching a wet/dry vacuum. Select a stand with an integral power strip and extendable arms to support lengths of molding. The Craftsman rig that I used included a 12-inch dual-bevel compound miter saw ($350) and a pro-duty saw stand ($250).
There are two ways to cut crown: Either lay it flat beneath the blade, or set it against the saw at the angle, the way it will be installed between the wall and ceiling. I prefer the latter. The flat method requires adjusting the saw blade to make both a bevel and miter cut; my way, the saw table acts as the ceiling, the fence is the wall, and an upside-down piece of crown can be cut at a compound angle with a simple 45-degree vertical chop.
To hold the crown in place, it helps to clamp a cleat to the saw table. To set this up, I first clamped a length of molding with its edges flush against the saw's vertical fence and horizontal table. I pressed a 30-inch, straight-edged board tight against the crown and clamped it to the table (2). This piece, the cleat, stayed in place between cuts, so I could easily drop each piece of crown into position. I cut away the center of the cleat by making a left-hand and a right-hand 45-degree miter cut, opening a channel for the blade to pass through (3).
Straight Runs
Most crown comes in 16-foot lengths, so unless you're trimming out a gymnasium, a single piece can usually span each wall. When it can't, two lengths join end to end in a scarf joint (4). This combines opposing compound-angle miters in a clean, nearly undetectable seam. Molding can shrink or shift out of position slightly—with a scarf joint, as opposed to a square-edged butt joint, a gap won't appear at the seam. To form a scarf joint, I made a compound-angle miter cut on the end of one length of crown. I nailed the crown to the backer board and then made an opposing compound-angle miter cut onto the end of the mating length of crown. After applying a little wood glue to the joint, I slid the second piece of crown into position and nailed it to the backer board.
Inside Corners
A coped joint connects two pieces of crown molding at an inside room corner. I prefer this type of joint over a miter joint because wall corners are rarely perfectly 90 degrees. A coped joint, in which a piece of crown is tailored to fit an adjacent profile's curves, makes a tight-fitting seam even if the inside corner is out of square—as many are.
I cut the first length of crown with a square end, pushed it tight into the corner and nailed it in place. Then, I cut a compound-angle miter into the end of the mating length of crown (1). Next, I used a coping saw to back-cut the molding along its contoured profile (2). The idea is to saw away enough wood to allow the coped cut to fit tight against the profile of the first piece of crown.
After cutting, the coped piece needed a little fine-tuning before it fit snugly. I smoothed the coped joint with rat-tail, half-round and flat files, as well as a wood dowel wrapped in 80-grit sandpaper (3).
Outside Corners
Outside wall corners are seldom perfectly square, so simply cutting both crown pieces to 45 degrees usually won't cause them to meet snugly at the corner. A technique that I've used for years measures perfect outside miter joints, regardless of the wall angle. I hold two overlapping 20-inch-long 1 x 4s against the ceiling at the corner. I trace both edges of the bottom board onto the top board (4), then draw a diagonal line to connect the two marks. Then I stack the 1 x 4s on the miter-saw table, adjust the saw blade angle to match the diagonal line and cut the 1 x 4s (5). I test-fit the 1 x 4s by holding them against the outside corner and checking the seam. If their edges don't make tight, even contact, I adjust the saw for a second cut. When the 1 x 4s fit on the wall, I lock the saw-blade angle and make a cut into one of the lengths of crown. Then I adjust the saw to make an opposing miter cut—at the same angle—into the end of the mating piece of crown. With the first piece of the crown's end sitting flush with the wall corner, I drill a pilot hole and hand-nail it to the backer board with 1½-inch 4d finish nails (fired nails can deflect and break through the face of the molding).
I add wood glue to the joint, slide the mating piece of crown into place (6) and nail it to the backer board.
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