When you shop at your home center or a lumberyard for baseboard molding you’ll notice that they come in extremely long lengths, sometimes up to 16 feet. The reason is that baseboard molding looks best if it is run as a single, unbroken piece along an entire wall. But in many cases, this is not possible. When the wall is longer than the available baseboard molding, you will need to splice two shorter baseboards together to stretch from end to end. The best way to do this is with a scarf joint, a method of joinery in which the boards meet at ends cut at opposing angles rather than with square-cut ends.
Scarf Joints vs. Butt Joints
Beginners may be tempted to use a simple butt joint in which two square-cut pieces are simply butted together, but this is the worst kind of joint for baseboards. For one thing, because the pieces aren't overlapping, it is difficult or impossible to push them together to create a tight joint. And if the wood shrinks even the slightest bit along its length—a common seasonal phenomenon—the joint will open up and leave a dark, noticeable line.
By contrast, a scarf joint is cut so that there are overlapping surfaces where the boards meet. If the wood shrinks, you still see a wood surface rather than a gap. A scarf joint also can be glued for added strength; the angled cut helps the glue bond better than trying to glue the end grain, which doesn't adhere very well. Finally, the thin edge of the front piece on a scarf joint is easy to sand flush if the boards aren't perfectly aligned.
Tools for Making Scarf Joints
The best tool for cutting the angles for a scarf joint is a power miter saw. But if you don't have access to this tool, you can use a simple miter box and hand saw. A good scarf joint requires precise 45-degree cuts, and these are very difficult to make without a miter saw or miter box.
For nailing the baseboards, an air compressor-driven or electric nail gun is far preferable to hand-nailing with a hammer and finish nails. The reason is that hand-nailing lightweight wood such as trim causes it to rattle and move out of position. The fast, decisive strike of a power nail gun fixes the baseboard in place before it can shift out of position.
That said, there's no reason why you can't create a perfectly good joint with a hammer and nails. If you choose this route, it's best to hold the pieces firmly in place where you want them and drill pilot holes for the finish nails. This helps the nails go in smoothly. After the nails are driven, recess them slightly below the wood surface with a nail set to hide the nail heads.
Equipment / Tools
- Tape measure
- Power miter saw, or miter box and handsaw
- Nail gun, or hammer and nail set
- Wood glue
- Baseboard trim
Plan the Joint Location
Measure for the first board so that the end joint will fall over a wall stud, if possible. Locating the joint over a wall stud allows you to nail into the stud (not just the wall plate along the floor) to help secure the entire joint. If this is not possible, you can still make the joint, but make sure you are anchoring the pieces into the bottom wall plate.
It is often easiest to prime and paint baseboards before you install them. Although some touch-up will be needed at the joint locations, it is easier to do the bulk of the painting before the baseboard pieces are installed.
Cut and Install the First Board
Cut the end of the first baseboard at a 45-degree angle with the bevel facing the room; the side with the point goes against the wall. Position the board against the wall and fasten it to the wall plate and studs (as applicable) with a nail gun or hand-driven finish nails. Don't nail within 6 feet or so of the beveled end so you can adjust the board for a good fit at the scarf joint.
Note: With the end of the baseboard that fits into the corner, you have two choices for attaching it to the baseboard on the perpendicular wall. You can square-cut the end so that the perpendicular baseboard will fit with a coped joint. Or, you can miter-cut both pieces at the inside corner.
Cut and Test-Fit the Second Board
Measure and cut the second piece of baseboard, also at a 45-degree angle, but with the bevel facing the wall, so that it will overlap the exposed miter on the first piece. Set the second board in place, testing the fit of the scarf joint. If the second board is too long, shave off a bit with the miter saw and re-fit the joint.
Glue and Nail the Boards
Apply a thin layer of wood glue to the bevel of the second board. Fit the boards together so the joint looks pleasing, then drill pilot holes and drive two nails at the joint, driving them through both baseboard pieces and into the wall stud, if possible. (If you are using finish nails and hammer, make sure to drill pilot holes for the nails.)
Nail Rest of Second Board
Nail off the rest of the second board, then go back and nail the remainder of the first board to within a foot or so of the joint.
Scarf joints can be used to join other types of molding. For example, this is a good method to use for ceiling crown moldings or chair rail moldings.