Expert: Jamie Yocono - 1/19/2006

Question
Is there a difference between a "tongue and groove" joint and a "mortise and tenon" joint?  Which expression is used more frequently in the trade?

Answer
Hi Phillip,

What an interesting question! I guess I've never really compared the semantics of a tongue and groove joint to a mortise and tenon joint.

To answer your question- yes, there is a difference between those two types of joints. A tongue and groove most often refers to a joint that is machined with the grain of wood, and is often open on each end.  Think of 2 long boards that could be used in paneling the front of a house. One board would have the tongue along it's length, and the other would have the groove along it's length. As they fit together, these two would intercept each other along that length. It's perfect joint for dealing with the seasonal humidity changes that often affect wood.

Wood will slightly swell with humid conditions, and slightly shrink with dry conditions. Think about that door that sticks during certain parts of the year, or that drawer that is sometimes hard to open. Seasonal movement if to blame. So when you're using solid wood for paneling, be it in a piece of furniture, or on the front of a house, the tongue and groove joint allows the wood to move slightly, and yet protects from gaps developing. It's quite an effective method.

A mortise and tenon, on the other hand, is similar, yet has quiet different applications. A mortise is nothing more than a hole (or a recess) in a piece of wood (it's often square) that is designed to receive another piece of wood into it. The piece of wood that it receives is called the tenon. Think of a square hole, with a square peg fitting into it. The fit is usually quite snug, creating a very strong joint.

Joints get a good deal of strength from the gluing surface that they contain. A mortise and tenon joint contains quite a lot of wood-on-wood surface, thereby making it very strong. It's one of the more common joints used in fine woodworking, such as furniture.

As far as comparing the two expressions, as to which expression is used more frequently in the trade ... that's a great question. I would have to qualify that a couple ways. If you asked the average person on the street if they knew what each one of those terms meant, I think tongue and groove would be the more widely known phrase. But if you asked a woodworker which phrase is more commonly used, he would probably say the mortise and tenon.

I'm sure that's a very subjective opinion. There are so many ways to do woodworking- a carpenter would use a Tongue and groove more often, a cabinet maker would refer to mortise and tenons more often.

Either way- good question. Quite thought provoking.

Good luck, I hope this helps. Feel free to write back with any other questions you might have after reading this.

Jamie Yocono
Wood It Is! Custom Cabinetry
www.wooditis.com
Las Vegas, NV