Tips for Installing Crown Molding
Compiled and illustrated by Loren Hutchinson

Proper installation of crown molding can be a mystery to the first timer. The following question was asked by Jason Falejczyk, and the responses he received tell a lot about how the process is done.

Jason Falejczyk asked:

I'm attempting to cut some crown molding with my mitre saw, not flat on the table, but angled between the fence and the table. The problem is the two angles don't add to 90 degrees. If I lay the bottom of the molding flat to the fence, the top doesn't lay flat to the table, and vice vera. So my question, should I position the molding flat to the fence, or the table.

I just called my hardwood dealer explaining how the addition of two angles are more than 90 degrees. They said it's supposed to be back beveled a little in order to make for a tight fit. I understand back beveling for that purpose, but I'm a little concerned about when it wraps around an outside corner: will it show a gap. Oh well, only one way to find out.


Steve, Furniture Crafters, Dallas, TX

Jason, you should be able to place the crown molding between the fence and the table just like between the wall and ceiling except upside down. Pretend the table is the ceiling and the fence is the wall.Now when you make a 45 cut it will be oriented properly.

Stephen Thomas

Actually, most wall/ceiling junctures run somewhere around 92* to 95* on the really bad ones today. Stick a framing square up and and check the corner at a number of places around the perimeter of the room. What happens is that even if the framing of the house is square, (pretty likely) the drywall finishers tape the corner, then bury the tape, then feather this out into the rest of the surface. So in the corner, the mud may be 3/16" (or even 1/2") thick, feathered both ways to nothing in 8" to 12", leaving greater than a true right angle. Yes, I"ve worked in lots of expensive places with true lathe and plaster work, and the work is usually more "craftsman" like, but not always any squarer.
[Figure 1]

Knowing this, A custom shop making millwork often makes the back angle more than 90* (95* is not untypical-see Figure 1) - you want the top and bottom edges to touch before the inside edges bottoms out, leaving a gap. You also need to carry a block plane and scribe or cope each edge of the trim to its mating surface if the work is stain grade or to be finished natural.

Generally, the ceiling is the reference for the mitre angle, so you would want that surface flat to the table. Practically speaking, it may be necessary to split the difference. Position it by hand, or stick a splinter or paper match somewhere to keep it from rocking. Also, except in rare circumstances, you will need to shoot the miter with your razor sharp block plane to make small corrections. After you have coped the molding to the wall, twisted it slightly to compensate for other imperfections, and made the angle slightly more (or less) acute than 45* because the outside corner is also not square, you cannot expect to find the correct position on a miter saw as quickly or optimally as you can hand shoot the joint. There a lot of little adjustments you can make if a joint is almost, but not quite, there. For instance: outside corner to outside corner a piece is a smidgeon too short (we're talking 1/32's). Plane the inside bottom of the molding (wall juncture) of the three pieces slightly and the joints will close up because the corners are brought in closer to the wall. You can't fix a botched job this way, but you can improve dramatically an "adequate" installation. If the job is botched, recut the pieces while they are still useful for somewhere else, and start over

If your walls and ceiling are dead square, then just choose one back surface of the molding and adjust the angle with a jack plane. 32 ft might take you 15 minutes, including time to think of a stable approach.

It is poor form (shoddy workmanship) to miter inside corners, they should always be coped. It's easier, it allows for slight wood movement, and it allows you to perfectly match the outside corners by allowing some slight leeway in the length of the piece that will be covered by the cope.
[Figure 2] Just turn the molding upside down (ceiling surface flat to the table - see figure 2) and make an inside miter cut. Now don't move a thing except the waste piece. Sit there and visualize how this piece will cover its mate (the cope cut - see figure 3). You will see that if you take a coping saw and keep the blade parallel to the mitersaw table, and perpendicular to the molding, you can cut along the molding edge intersection with the miter cut, and make a perfect cope. To help visualize, take a pencil and blacken all of the mitered surface. Cut all of this away by cutting along the molding profile.
[Figure 3]
[Figure 4] In practice, make your miter cut a little long, then adjust to fit with whatever it takes, usually a sharp chisel, sometimes (judiciously)a gouge or rolled coarse sandpaper. It is also usual to slightly undercut the profile so just the visible edge contacts (see figure 4).
[Figure 5] Then if the cope is carefully cut, and slightly jammed to its mate, it will essentially self form the last little increment to fit (see figure 5).

I usually cut any cope cut first, and the other end last, That way if the cope goes really wrong, it can be recut before the stick is too short. It is seldom necessary to make a cope cut on both ends of a molding if you have planned the room right. When it does happen, it is usually the last piece, and there will have been ample time to figure how the ceiling rolls, so to speak, so you can guess pretty well where to compensate. This brings to mind, of course, Always do your longest runs first; hopefully your closing pieces will be short ones and you will have three or even four pieces of short end to get it right without actually wasting anything.

Bob Tingle

When coping molding corners, I plan it so that, when entering the room (or from the most frequent viewing point) the viewer looks along the coped molding, and into the solid member behind it. In other words, If you look along the first piece put up, you are looking into the crevice and will notice any irregularities. But if you are sighting along the second member installed, you hardly notice the joint. So I plan the cutting of the coped joints to be most pleasing to the eye from the most frequent view point (usually the point of entry into the room).