Terms of the Trade: What Is A Mortise?

wood pieces with mortise and tenon joint

A mortise is the second part of a mortise and tenon joint. The mortise lock is the square hole, or cavity, in which the plug, or tenon, is inserted. This type of joint has been a staple in construction for thousands of years. It has been a traditional joining technique used by masons and carpenters since prehistoric times.

Types of Mortise

An open mortise has only three sides like a birdie joint. It normally is a slot cut into a piece of wood to accept a tenon forming a 90-degree corner.

A stub mortise is very shallow hole that does not go all the way through a piece of lumber or wood.

A through mortise is a hole that is completely cut through a piece of lumber or wood

Mortise Cut

The mortise is cut in either the face, edge or end of the second piece that will make the connection. A popular spot is in the edge of the second piece. The mortise must receive the tenon snugly so there needs to exist enough friction to hold this joint together. But, it shouldn't take any pounding to fit the tenon in the mortise. The mortise should also be the same thickness as the tenon. It should also be the same width as the tenon, however, the length needs to be from 1/32 to 1/16 an inch longer. This will prevent the tenon from bottoming out of the mortise.

Mortise Locks

The word mortise can also refer to a popular, secure kind of lock, in which the bolting mechanism is contained mostly or entirely within a door.