DIY Installing Crown Molding

On this page you'll find illustrated, step–by–step instructions for cutting and installing standard 52° crown molding. Included are angles and compound miter saw settings for cutting inside and outside miter joints.

Use a Compound Miter Saw

To form the angles required to install crown molding the wood must be cut in two directions at once; first it must be beveled and second it must be mitered.

These angles can be difficult for some do–it–yourselfer's to cut with a standard miter saw or coping techniques. Fortunately, a compound miter saw makes cutting these complicated angles as simple as setting two guides on the saw.

With a compound miter saw, trim boards can be cut while laying flat on the saw table because the saw blade tilts to the necessary position to make the cut instead of having to prop the board at the correct angle.

A typical compound miter saw will have a stop on the bevel and miter guides for setting the proper angles of cut for both 52° and 45° crown. A gauge on the back of the saw sets the bevel position of the blade and the table pivots left and right to set the miter position.

The following installation process is for standard crown with a 52° angle on the top, ceiling edge and a 38° angle on the bottom, wall edge like these crown profiles.

Setting the Saw

Set the saw by tilting the blade and setting the bevel angle at 33.86° using the guide on the back. Leave the bevel setting at this position throughout this installation procedure. Some compound miter saws have a double bevel feature. This means the saw blade can be tilted left and right instead of just to one side. When using a double bevel saw for the following procedure, use only the left bevel position.

Set the miter angle by moving the saw table left and right of center. The position will alternate depending on which corner piece will be cut. Set the saw table at 31.62°–right to cut the piece that will form the right inside and left outside corners, pieces C and D pictured here. Cut these pieces with the molding's ceiling edge against the saw fence.

To set the saw for the matching pieces, slide the saw table to the left and set it at 31.62°. With this setting the left inside and right outside corner pieces, A and B, can be cut. Turn the piece so the wall edge is against the fence to make these cuts. Notice that the inside corners, A and C, will always be on the left of the blade and the outside corners, B and D, will always be on the right.

Cutting Inside Corners

Starting at the right corner of one wall, measure to the next corner. Have a helper hold one end of a tape measure to get an accurate measurement. Use this measurement to choose a board to run the length of the wall. If one is not available, combine 2 shorter pieces using the technique described below.

With the profile facing up, cut the right end of a board to form piece C using the settings for a right inside–left outside corner. Place the ceiling edge against the saw fence and make the cut as close to the square end of the board as possible to avoid waste. Leave the piece flat on the saw after making the cut to measure and mark the opposite end for the next cut.

All measurements for inside corners should be made using the wall edge as the reference. Hook a tape measure over the end of the board and mark the other end with a thin pencil mark. Set the saw to cut piece A at the opposite end by sliding the table to the left and setting it at 31.62°. Leave the blade bevel set at 33.86°. Turn the piece around and place the wall edge against the saw fence. Site along the blade to line it up and cut outside the mark. Install the piece using the instructions below.

Coping Inside Corners

It is also possible to use a coped joint to make inside corners. Coping a wood joint requires cutting out along the profile of one of the pieces so it butts against the other piece to form a seamless 90° union. Before cutting the profile the piece must be cut with the same compound miter as above to make the union work.

Coping an inside corner on crown molding can be difficult but it can be done with some patience. This can be worth the trouble as, theoretically anyway, miter joints can develop cracks and coped joints won't. However, gluing a miter joint will greatly diminish the possibility of cracks developing and the same extremes in environmental conditions that make miters crack will make other wood joints crack as well.

Cutting Outside Corners

All measurements for outside corners should be made using the ceiling edge of the piece as the reference. To cut a left outside corner, piece D, slide the saw table to the right and set it at 31.62°, leave the blade bevel set at 33.86°. Place the ceiling edge of the board against the saw fence and site along the blade to line it up and cut just outside the mark on the ceiling edge.

To cut a right outside corner, piece B, slide the saw table to the lefts and set it at 31.62°. Measure and mark the ceiling edge of the molding. Set the wall edge against the saw fence and line up the blade. Cut just to the outside of the mark.

Finished Outside Corners

To terminate the molding at the end of a wall, measure the wall and subtract an eighth inch. Cut a board with the appropriate outside corner to this length and install it using the instructions below. Measure the distance from the wall to the face of the installed piece.

Cut the end cap with a matching outside corner using a short piece of leftover trim. Be sure the piece is long enough to cut safely with the saw and make the cut on one end. Mark the length using the measurement taken above and cut the other end at 90° to fit flat against the wall.

Check the fit and then caulk the ceiling edge of the end cap. Brush the joint face of both pieces with a thin coat of wood glue and press the end cap in place. Wipe off any excess glue and oozing caulk with a clean, damp rag.

When working with stain grade trim, avoid using too much glue on the edges to prevent oozing. If bare wood absorbs the water–based glue or caulk it won't absorb enough stain and create white blotches in the finish.

Don't nail these small in place, tape the joint together with painter's masking tape at the corner, ceiling and wall until the glue is dry.

Combining Two Pieces of Molding:

If two pieces of trim will be needed to run the full length of a wall, they should be joined with a mitered or scarf joint, rather than a straight, butt joint. A scarf joint will blend the two pieces together so that the union is undetectable.

To join the two pieces set the saw for a right inside–left outside corner. Place the ceiling edge against the fence and slide the right end of the board under the blade. Make the cut to form piece C. Cut the second piece to be joined setting the ceiling edge against the fence and slide it so the left end is under the blade to cut piece D. Temporarily join the two pieces on a flat surface to measure and mark them for installation. Glue the edges just before installing the trim and nail the two pieces together with small brad nails.

Preparing to Install the Molding:

Locate and mark wall studs and ceiling joists using a pencil. To find the framing, use a stud finder or tap across the wall or ceiling and listen for a difference in the sound produced. In general, a hollow sound indicates a space behind the wall and a sharp sound indicates framing. The difference between the sounds gives one a rough idea of the location of a stud or joist. Use a drill and an eighth inch bit to bore into the wall where you expect to find the framing. If the drill passes straight through, keep drilling at one inch intervals until you hit wood. Mark the location of each stud and joist with a pencil mark that can be seen when the trim is in place.

Before installing paint–grade crown, caulk along the two edges that make contact with the wall and ceiling. This will ensure that the boards stays in place and will also serve to fill gaps caused by rough or irregular surfaces. Use these caulking techniques to smooth out excess caulk that squeezes onto the walls and ceiling.

Install the molding holding it up and shifting the placement until the edges lay flat against both the wall and the ceiling surfaces. Drive a nail through the board and into the wall and ceiling about 2 feet out from each corner. Leave the ends loose to allow for adjustments when joining the matching corner pieces. Drive nails at about 16 inch intervals into the wall and the ceiling to secure the middle of the board. Some nails can be driven into the plaster or drywall but these should be kept to a minimum. To ensure that the trim stays in place, be sure nails are driven into wood framing at regular intervals across the wall and ceiling.

At the corners, shift the boards to expose the ends enough to brush the both edges with a thin coat of wood glue. Join the corners adjusting the two piece together until they form a smooth union that lays flat against the walls and ceiling. Nail both pieces to the walls and ceiling at the corner. Smooth out any caulk that squeezes out before it has time to set.

Driving Nails:

Nailing crown in place will be much easier with the use of a pneumatic nail gun. These tools will drive and sink the nails, all in one easy motion. A nail gun with a mid–range capacity to fit 1½ to 2½ inch finishing nails, is a good choice for this and most other decorative trim projects. If no nail gun is available, drill pilot holes and drive 2½ inch finishing nails with a hammer. Counter sink the nail heads and fill them with painter's putty before painting.

Correcting Cutting Mistakes:

If the piece you've cut is just a little too long, put it back on the saw and line up the blade to take just a tiny bit off and try the fit again. You can usually sneak–up on the right length in this way. If the piece is much too long, measure the wall the piece again to determine where to make a better cut.

If the molding is too short, caulk can sometimes work to fill small gaps but if there is a large gap in the joint, cut a new piece to correct the error. Salvage any short pieces by joining them with a scarf joint to make longer pieces or use it for short runs.

A Word About Measurements:

When measuring walls at inside corners it can be hard to know exactly what point to use as the reference mark. Most plaster and drywall corners are rounded, not square making it difficult to get an accurate measurement. To avoid cutting a piece too short, always used the most extreme point as the reference point. The piece can always be trimmed slightly if it turns out to be a bit long when installing.