Crown molding provides a dramatic finishing touch to interior spaces, but the installation process can be intimidating to anyone who has not attempted it. The large, often complex, molding profiles available in crown molding (there are many), and compound-angle miters where pieces join, are difficult to accurately measure, cut and install. However, there are ways to make the process easier and accomplishable with a little practice.
Find the right size molding for your style home. Decorative and ornate molding will generally look better in older, period homes. Simpler, clean-lined molding works best in newer or mid-century homes. The size of molding will depend on the height of your ceiling — the taller the ceiling, the wider the crown molding. Molding comes in hardwoods like pine or oak. If you're going to paint the molding, you can save money by using a lower grade wood or medium-density fiberboard (MDF). If you are going to paint the molding, buy pre-primed materials to save time.
To determine how much molding you will need, measure the room to get the total linear footage. Add 15 to 20 percent for waste and mistakes.
First and foremost, it helps to use a compound miter saw to cut crown molding. This saw can be adjusted to make clean, perfect cuts of multiple angles at once. Because the molding is installed at an angle to both walls and ceilings — a task complicated by the fact that individual pieces also meet at other intersecting angles in both inside and outside corners — you need a tool that can handle these multiple-axis or compound cuts.
Many carpenters use a simple trick to form compound angles — they cut the molding upside-down and backwards. By placing the molding’s bottom (or wall-facing) edge against the saw’s vertical fence and the molding’s top (or ceiling) edge flat on the saw table, you can make a standard 45-degree cut (Image 1) that will fit most intersections when the molding is placed right-side-up. Place a piece of painter's tape on one side of the molding to make it easy to remember which is top and bottom. If you need, make a few practice cuts using scrap pieces of molding.
Inside corners are best handled with “coped” cuts. This method creates a profile on one piece of molding that closely matches and overlays on top of another molding length.
To make a coped inside corner, start by cutting a square 90-degree angle (Image 2) on the end of the first molding piece, then install this end tight against the corner. On the second piece of molding, make a 45-degree-angle cut so that the exposed cut faces outward. Then use a thin-blade coping saw to back-cut at an angle along this face, following the molding’s profile (Image 3). Use a wood rasp or sandpaper to trim the cut, if necessary. The resulting profile should fit tightly over the intersecting molding when installed.
Another method for fitting together inside corners is to cut both pieces at opposing 45-degree angles with the molding placed upside down on the saw. If the intersection isn't tight, you will have to caulk the gap and paint over it.
Most outside corners can be joined with mating 45-degree-angle miter cuts. If the wall angle is slightly off, adjust the cuts on both molding faces equally by one degree at a time until you have a close-fitting joint (Image 4). This is easily done on a power miter saw, which can be adjusted to cut across a range of fractional angles.
Remember, on outside corners, the point of the molding will be towards the ceiling. On inside corners, the long point is going to be towards the floor.
Before installing crown molding, test fit a piece of molding in place (Image 1), and mark the height of the molding where it meets the wall below the ceiling. Use a level, or laser level, to extend this mark along the walls from corner to corner (Image 2). Use an electronic stud finder to mark all wall studs and ceiling joists (Image 3) along this line. These marks will be your nailing points when the moldings are installed. Some carpenters prefer to install wood blocking against the wall and ceiling joint to serve as a secure nail base for the molding (Image 4). Use wood blocking if your molding is wider than 4-3/4 inches.
Where horizontal or “running” lengths of molding meet, join them together with overlapping (lap joints) 45-degree-angle cuts (Image 5). This will prevent visible gaps from opening at the joint as the molding dries and shrinks. Apply construction to the inside of the 45-degree cuts to get a tight seal then secure the pieces together with finish nails. For corner seams, apply caulk to the coped end (Image 6) then secure with nails. Wipe away any excess caulk that may ooze out of the seam.
Wall corners are rarely perfectly square. To avoid problems and wasted material, first cut and join short random-length molding pieces and pre-construct sections to fit all outside and inside corners. It is easier to work with short pieces and make trial-and-error cuts if necessary to get a tight fit in each corner than to attempt to make longer lengths meet precisely. After cutting the corner pieces, glue and nail them together, then cut 45-degree overlapping angles on the outer ends where they will be joined to intersecting running lengths. If you opt to build all of the corners at one time and install them afterward, mark each corner according to its location.
If you use a hammer and finishing nails to install hardwood molding, use a drill to pre-bore nail holes to prevent the wood from splitting. A pneumatic finishing nailer is the preferred tool for installing moldings. It makes working overhead much easier, prevents hammer marks, and eliminates pre-boring because power-driven nails will not split the wood.
Use wood putty or paintable caulk to fill slight gaps where moldings intersect. Use spackle to fill in the nail holes if you are painting your molding. If you have any nails protruding from the molding, use a hammer and nail set to the recess them. Caulk along the top and bottom edges to seal the moldings against the wall and ceiling.