When joining sections of baseboard molding at inside wall corners, you have a choice between creating a mitered joint, or a coped joint. When cut properly, the two methods produce joints that look largely the same. Which method you choose will depend largely on your skill level and on the tools you own.
What Mitered and Coped Joints Are
Both types of joints can be used to join segments of the molding at interior corners that are set at roughly 90 degrees. The differences between mitered joints and coped joints are fairly simple to understand: The mitered joint requires both sides to be cut at around 45 degrees and the coped joint requires only one side to be cut to conform to the other side.
With inner mitered baseboard joints, each baseboard piece is cut at a 45-degree angle. When joined, the two pieces form a 90-degree angle that fits perfectly against the inside corner where two walls meet.
Mitered joints work well when the walls meet at exactly 90 degrees. But where walls are not perfectly square, achieving a perfect mitered joint may require some adjustment to the cutting angle on the baseboard pieces.
For example, if a wall meets at an 86-degree angle, the baseboard pieces need to be cut at 43 degrees in order for them to make a perfect joint.
Mitering is also the only method of the two that can also be used on outside corners—where molding pieces meet on the outside corners, such as in L-shaped rooms or where baseboards follow the profile of partial walls on archways.
With inner coped baseboard joints, one baseboard is cut to a 90-degree angle, while the adjoining baseboard is manually cut so that it molds to the shape of the first baseboard.
Each baseboard is first cut square, at a 90-degree angle. Then, one piece of the baseboard is positioned so the square end rests in the wall corner against one wall. Finally, the adjoining piece is manually cut with a coping saw so the end conforms to the profile (contour) of the first piece.
Coping can be a good choice when walls are not perfectly square. Coped joints are also less susceptible to gapping when changes in humidity cause wood moldings to expand or contract.
Should You Miter or Cope Your Baseboards?
Many professionals swear by coped joints since this method is well suited for all types of wall conditions. Above all, professional carpenters want to avoid call-backs to solve problems, so they generally opt for the method that gives the best results.
For do-it-yourselfers, coped joints can be tricky to cut perfectly. If you attempt coping, make sure to practice your technique on scrap wood. If you get good results, coping is the way to go. If you find coping difficult, you will be best served by using mitered joints for your baseboards and coped joints only when absolutely necessary.
Mitered-Cut Baseboard Details
Easy to cut
No manual cutting
Fits well with a majority of walls
Difficult to fit walls other than 45 degrees
Less stable with expansion and contraction
If looking at a mitered baseboard joint from above, the L-shape is perfectly 90 degrees and there is no gap between the two boards.
Much of this depends on the room's corner and whether it is a perfect 90 degrees, to begin with. Viewed from the front, there is little visual difference between this mitered joint and a coped joint.
How to Make a Mitered Joint
With either a manual miter saw and miter box, or with a power miter saw, cut each baseboard pieces at a 45-degree angle. Fit the two pieces together to form a seamless 90-degree-angle corner. Some slight adjustment of the cutting angles may be necessary if the planes of the wall are not at a perfect 90-degree angle.
Miter joints are very easy to make, provided that the walls meet at a perfect 90-degree angle and your miter saw is calibrated correctly so that it cuts at angles that exactly match the miter scale.
However, if the walls do not meet at 90 degrees, or if the saw does not cut at precise angles, you may be left with a gap in the corner.
Seasonal expansion and contraction of wood moldings can also cause visible gaps to open up. With painted baseboards, you can disguise such gaps with a small bead of caulk.
Coped Baseboard Joint Details
Stable when wood expands or contracts
Difficult to learn
One piece of the baseboard will be square-cut to fit flush into the corner, while the adjoining piece is contoured to fit the profile of the molding.
When cut correctly, a coped joint looks very similar to a mitered joint, though a trained eye may be able to distinguish the craftsmanship involved.
How to Make a Coped Joint
Cut one baseboard piece at 90 degrees so that it will butt into the wall corner. Use this baseboard piece (or a short scrap piece of identical molding) as a template to draw a profile of the molding shape on the face of the second piece of baseboard.
Next, use a manual coping saw to cut the second piece along the marked line. Make sure to keep the saw blade angled slightly inward (back-beveled) from the front face of the molding, ensuring a sharp edge that will fit tightly around the adjoining molding.
Fit the second piece of baseboard molding into the corner, so that the shaped end fits around the contours of the first piece. If cut correctly, the coped joint should fit tightly, with no visible gaps.
Some carpenters make coped cuts by first cutting the molding piece at a 45-degree miter, then using the coping saw to cut precisely along the line where the saw blade has sliced into the molding. The edge of this miter cut will conform exactly to the molding contour once you cut along it with the coping saw. When using this technique, a carpenter normally cuts the baseboard piece an inch or two longer than the required length. Once the piece is first mitered then coped along the edge of the miter cut, the other end is square-cut to fit the precise length needed.
Cutting a good coped joint is admittedly a bit tricky if you don't have experience. The flexible blade of a coping saw can be difficult to control. For best results, you need to back-bevel the cut to ensure a sharp edge that fits tightly around the adjoining piece of baseboard molding.
It is best to practice on scrap pieces of baseboard before coping the long piece of molding you intend to install.
If done perfectly, coped joints are preferable to mitered joints, since they are less likely to reveal gaps due to imperfect wall angles or seasonal expansion and contraction of wood.