How to Join Baseboards With a Scarf Joint

Contractor cutting baseboard

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When you shop at your home center or lumberyard for baseboards, 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 baseboard, 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 overlapping surfaces where the boards meet. If the wood shrinks, you still see wood 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 flush.

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 expensive power 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.

Tools and Supplies You Will Need

  • Baseboard trim
  • Tape measure
  • Pencil
  • Miter saw, or miter box and handsaw
  • Nail gun, or hammer and nail set
  • Wood glue

Instructions

  1. 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.

  2. 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.

  3. Cut and Test-Fit the Second Board

    Measure and cut the second baseboard, also at a 45-degree angle, but with the bevel facing the wall. 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.

  4. 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 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.)

  5. 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.

Tip

It is often easiest to prime and paint baseboards before you install them. Although some touchup will be needed at the joint locations, it is easier to do the bulk of the painting before the baseboard pieces are installed.