my Old Workshop

Cut perfectly fitting crown molding corners

We’ve talked before about how coping trim is the more traditional and craftsmanlike approach to corner joints. But with newer materials, such as MDF, which don’t shrink, you can still rely on the basic miter cut for inside and outside corners.

However, if you’ve ever attempted to install baseboards, or ceiling crown or cove molding in particular, you may have become frustrated. Even a perfectly cut 45-degree angle often doesn’t seem to fit properly. Here’s some help which will give you perfect corners every time.

There are two reasons for the hassles encountered when trying to miter for a 90 degree corner. First of all, most corners in houses aren’t 90 degrees. Usually they’re a little wider, or a few degrees more than 90. Sometimes, this occurs because the drywallers have laid a thicker coat of mud in the corner, and feathered it out to the plane of the wall within a foot or so.

Secondly, the ceiling itself is not always perfectly level, and if you run your trim along it, you may have two pieces meeting in the corner coming from different horizontal planes, making a perfect corner nigh on impossible.

Let’s start with the ceiling first. Using a laser level (ideally) find the lowest point of the ceiling, and draw a line at this level. Hopefully it’s not more than a fraction of an inch off at any point. If so, you can put your trim at this level, shimming as necessary, and caulk the gap for a clean look. And your molding will come into the corners “on the level”.

Now you need to measure the corner angle. A good tool for this is a large acrylic protractor which looks like two rulers. You spread it in the corner, lock it, and read your angle. To get the best reading, first hold up two 3′ pieces of straight wood on the wall so that they meet in the corner, and measure the angle off these.

With the actual angle in hand, you’re ready to cut. Sometimes, people cut crown molding by holding it on an angle against the saw table and fence — in effect upside down, with the fence acting as the wall and the table acting as the ceiling. If you’re doing that, you simply divide the angle in half and swivel the saw blade accordingly. But holding your trim this way can be awkward. Cutting it on the flat is better, and you can do it with a compound miter saw. Next time, we’ll show you how to figure out your angles, and give you some more crown molding tips.