If you want to install crown molding as a do-it-yourself project, it's moderatly difficult.
The molding gives a room a finished, elegant look. While molding used to be standard installation in homes, modern construction considers this detail an extra and often leaves it for homeowners to install later or do without. A home with crown molding, however, looks expensive and polished compared to typical new construction.
Tips for crown molding installation
If expense is an issue, look into medium density fiberboard (MDF) instead of wood. MDF can't be used in kitchens or bathrooms since humidity will warp it. Also, in the Atlanta area, if you tend to leave your heating and air conditioning off during humid months, you may want to avoid MDF due to the potential for warping because of the humidity.
Step 1: Measure & Cut
Instead of using a tape measure, measure and cut in place. Measurements can leave you open to mistakes, while holding the molding up to your wall or ceiling joint and cutting in place is more accurate.
Cut the corners at a 45-degree angle to allow the crown to meet properly.
The way you've cut the molding, it's upside down. Understand and visualize how the pieces fit together before making your next cut.
Use a power miter saw and set the piece so it is set at the same angle that it will lay on the wall.
Note: Most walls don't connect at a perfect 90 degree angle. To make accurately angled cuts on uneven walls, trace two overlapping 1 x 4 pieces at the corner and connect the lines with a diagonal line from opposite corners. Cut through both pieces along the diagonal line and set the saw at that angle.
Step 2: Connect the Joints
Next you'll cope the joint. When you cope a joint, that means that you're going to prepare the joints to properly connect. Take the angled end of one piece and stencil the angle onto the other piece. Darken the edge with a pencil and cut it with a coping saw. You want to leave the line, and remove everything behind the line. Basically, instead of cutting a flat cut on the wood, you're beveling the edge to cut away the edge of the wood so the two pieces connect and lay flat against each other. Beveling is the process of applying a sloping or slanted cut, much like a picture frame can have a beveled (sloping) edge.
Step 3 Attach the Molding
Check the fit and, if it's ready, attach the molding to the walls. Before nailing it to the wall, bore two pilot holes through the point of the miter joint. A pilot hole is a drilled hole meant to create a guide for your nail so you don't split the wood. Apply glue to the joint and fasten each piece of crown with nails at the top and bottom.
Use paintable caulk to cover up any slight imperfections. You'll want to choose painted molding if you're a less experienced molding installer. Stained molding is necessarily a much more precise job since you can't cover up slightly irregular angles with painted caulk.
If you have walls longer than 16 feet, you'll need to create a scarf joint by mitering the ends of both pieces to connect them in a straight line. You'll cut these much like the coped joint, but instead of an angle that meets in a point away from the wall, you'll create complementary angles that meet against the wall.
Can't get that angle right at the corners? Use corner blocks. It's a small corner piece that's cut and angled for you. And even joined together. It's a lot simpler and can look more professional. It also saves a lot of time by allowing you to skip mitering and coping.
Once you're at the end of the molding board, create a return (or edge piece) if the end doesn't butt up to a wall. Cut another 45 degree angled miter on the end of the crown run. Then create an opposite 45 degree miter on a small return piece (just enough to butt up against the wall).
Bore pilot holes through the return and apply a thin coat of glue to connect the return. Then set your nails and fill all your nail holes with putty.
Molding can be a little more difficult in soffit and cabinets. However, the above tips and steps can be used for most wall molding.
You'll also want to keep in mind, before starting your project, that the crown will need to be nailed into studs along the bottom edge and ceiling joints along the top. If you want to avoid this step and avoid stud-finder work, install plywood backer board or furring strips to the top plate so you can nail the molding in wherever you like.
If you've decided that the project is beyond your abilities, contact licensed remodeling professional to install the crown for you for a professionally trimmed room.