What is a Scarf Joint?

M.R. Anglin

A scarf joint, or scarph joint, is used to join two pieces of wood or metal end to end. It is a simple form of a lap joint, and when the two pieces are joined together, produces a virtually invisible seam. Joiners can use this joint when the material they want to join is not long enough for the task at hand. It is also useful if material has been cut too short. In such circumstances, a the joint can be used to extend the materials to the desired length.

A half-lap joint is a common type of scarf joint.
A half-lap joint is a common type of scarf joint.

Joiners will create a scarf joint by first tapering the ends of the materials to be joined. The ends are then joined together and fastened. When this joint is used to join wood, the area can be glued together. A half-lap joint is a variation of the scarf joint. Other versions of the joint include the dovetailed scarf, the plated scarf, the tenoned scarf, and the double tenoned scarf.

The baseboards in many houses use a plain scarf.
The baseboards in many houses use a plain scarf.

There are two different categories of scarf joints: a plain scarf and an interlocking scarf. A plain scarf joint is made when two flat pieces of wood are joined at an angle. In order to stay together, this joint needs to be fastened with a substance like glue, screws, or bolts. An interlocking scarf joint also depends on its fasteners to keep the joint together. There are several types of interlocking scarf joints, including hooked, keyed, and nibble joints.

Plain scarf joints are not very strong and, as such, are often used for decoration. Some examples of its use can be found in trims or molding. In fact, the baseboards of many houses use a plain scarf. In this application, the two sides of the baseboard are cut at a 45° angle, one with the bevel facing the room, the other facing the wall. Then they are fitted together and nailed into the wall.

An interlocking scarf, on the other hand, has several uses. Three such interlocking scarf joints, the key scarf, the hooked scarf, and the keyed hook scarf, are used in ship building and boat building. The key hooked scarf joint is a combination of a key scarf and a hooked scarf. Both the key and the hook scarf are often used to create the backbones of many boats. Since the timbers being used in these applications are so long, these joints are usually closed by bolts.

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