When you're installing new baseboard trim, you're faced with the decision of how to do the inside corner joints: Should you miter them or cope them? Mitering is generally the easier and faster technique for beginners, while many carpenters prefer coping for inside corners. If you have a lot of baseboard to run, it might be worth the time to learn the coping method, even if you're a newbie to trimwork. Coping takes longer for each cut, but it's more foolproof.
A mitered joint is made with both ends of the molding cut at a 45-degree angle and fitted together to form a 90-degree inside corner. This is the type of joinery used in most picture frames and many other woodworking projects where perfect 90-degree angles are required. Making a mitered joint requires a miter saw of some kind, either a power miter saw or a hand miter box.
A coped joint starts with one molding piece that is cut square and simply butted into the wall corner. The mating molding piece is then cut to conform to the profile of the first piece, and it butts into the face of the first piece. The profile is cut with a coping saw or sometimes a jigsaw.
Pros and Cons of Coped Corners
Trim carpenters and other professionals often prefer coped joints because they tend to open up less than miters when the wood shrinks during dry weather. Coped joints also accommodate out-of-square wall corners better than miters, which require a 90-degree corner for a perfect fit. Finally, coping is the traditional method of baseboard joinery and is considered a mark of craftsmanship. For this reason, it is often preferred for work with historic or period moldings.
Places where coped joints are the best choice include:
- With wood moldings in climates with radical seasonal shifts in humidity levels. Large seasonal swings make it more likely that corner joints will visibly open up, and coped joints are less likely to show these gaps.
- Where walls are out of square. Many finish carpenters argue that coped joints are better able to accommodate walls that are out of square—where the planes do not meet at exactly 90 degrees. However, you can customize miters to fit out-of-square walls by adjusting the miter cuts a degree or two off of 45 degrees.
- Where the look of fine craftsmanship is desired. Period homes seeking to duplicate the look of original craftsmanship will benefit from using historically accurate joinery methods—using coped joints rather than mitered joints.
- For chair rails and crown moldings. Molding that is higher on the wall is much more visible than baseboards, and the perfectly shaped joints made by coping will be evident and appreciated by viewers.
On the downside, coped joints take more practice and skill than mitered joints. With miters, the saw does all of the cutting, and the trickiest part is taking accurate measurements and cutting the molding to the proper length. Coping requires a special technique and precise cuts made with a handsaw. Once you've mastered coping it can be just as fast as mitering, if not faster, but that kind of speed takes practice.
Pros and Cons of Mitered Corners
There is a reason why DIYers and production carpenters building stock houses use mitered corners on moldings: They are easy and quick to make. Modern power miter saws fitted with fine-tooth blades make quick work of cutting moldings to perfect angles for mitered joints. Even an inexpensive miter box and hand miter saw can make accurate miter cuts, but most of these can cut only 45 and 90 degrees; they can't make custom angles.
Places where mitered joints make the most sense include:
- With non-wood trim. Shrinkage is a moot point with polyurethane and MDF moldings, so this is not a reason to cope the joints. Poly doesn't expand or contract, and neither does MDF under normal conditions (though it may swell with direct water contact).
- Where skill is an issue. If you have a power miter saw, nothing can be easier than locking it to the 45-degree angle, pressing the baseboard against the fence, and sawing down to reveal a nice open angle. By contrast, copes are tricky and take practice.
- Where speed is important. Most homeowners making mitered joints will be finished with an entire room at the same time it takes to learn the basic technique of coping. Mitered joints are the quickest method for installing baseboards and other moldings requiring inside corners.
The biggest drawback of mitered joints is often realized when you nail the molding to the wall. If either of the two pieces doesn't remain vertical after it's nailed, the miter joint will open up. For example, if there's some thick drywall mud at the bottom of the wall and this forces the molding to lie back, even a little bit, the mitered joint will be open at the top. By contrast, coped joints tend to be less affected by imperfect walls.