How to Join Baseboards With a Scarf Joint

Scarf Joint

Lee Wallender

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 looks best if it is run as a single, unbroken piece along an entire wall. Unfortunately, in most cases, this is not possible. When the wall is longer than the baseboard, you need to splice two shorter baseboards together to stretch from end to end. The best way to do this is with a scarf joint, made with the two boards cut at opposing angles.

Scarf Joint vs. a Butt Joint

Beginners may be tempted to use a simple butt joint—where 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. Also, if the wood shrinks even the slightest bit along its length, the joint will open up and leave a dark, noticeable line.

By contrast, a scarf joint is made with overlapping surfaces so that if the wood shrinks, you still see wood rather than a gap. A scarf joint also can be glued for added strength, and the angle cut helps the glue bond better than if the wood were glued and butted (end grain doesn't glue well). Finally, the thin edge of the front piece on a scarf joint is easy to sand flush if the boards aren't aligned perfectly.

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 to make your joint, 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 shake out of position.

That said, there's no reason why you can't fasten a perfectly good joint with a hammer and nail. If you choose this route, it might help to hold the pieces right where you want them and drill pilot holes for the finish nails. This helps the nails go in smoothly, with much less banging around of the trim. After the nails are driven, set 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

Plan the Joint Location

Measure for the first board so that the joint will fall over a wall stud. This is optional but preferable. 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.

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.

Cut and Dry-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 to test 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 good, then drive two nails at the joint, going into the wall stud, as applicable. Nail off the rest of the second board, then go back and nail the remainder of the first board.