Traditional methods meet modern ingenuity at Eisenhardt Mills

May 23, 2018
Amanda Zimmerman
Traditional methods meet modern ingenuity at Eisenhardt Mills

The evolution of carpentry and millwork has given rise to various joining methods: dominos, dowels, biscuits to name a few. But for stile and rail construction, Eisenhardt Mills, Inc. prefers a method that stood the test of time: mortise and tenon joinery.

Favored by Egyptian kings, found in furniture within the tombs meant to last through the afterlife, mortise and tenon joints have been used for thousands of years, and can be found in the post and beam skeletal framework of many of the world’s extant historical structures.

The Power of Simplicity

Most commonly employed to connect two pieces of wood at right angles (90°), mortise and tenon joints are versatile enough to be used in angled joinery as well, such as in wall paneling at stairs. The tenon, a tongue cut into the end of a rail, muntin bar or similar piece, fits securely into the mortise’s square-shouldered or rounded hole.

Traditional methods meet modern ingenuity at Eisenhardt MillsThe simplicity of a mortise and tenon joint’s peg and hole construction has stood the test of time.

Traditional methods meet modern ingenuity at Eisenhardt MillsWith such a large surface area, the glued joints form a powerful and long-lasting hold.

Outlasting and Outperforming the Competition

While history gives us ample evidence of the staying power of mortise and tenon joints, their durability has also been repeatedly established in the controlled and measurable parameters of industry labs.

Recent testing by Dowelmax showed the mortise and tenon joint to be twice as strong as most modern joining methods, able to withstand over 1,000 pounds per square inch (psi) before giving way. The only joint that even came close in performance was a doweled joint using no less than five 4” dowels; others failed much earlier.  A pocket screw joint with five screws was only able to sustain 420 psi; a biscuit joint with a #20 biscuit failed at 485psi, while 600 psi was the breaking point for a festool domino.

Traditional methods meet modern ingenuity at Eisenhardt MillsThe strength of mortise and tenon joinery has been proved by time and industry testing.

A Benefit to Buildings & Builders

Because mortise and tenon joints create such a strong and lasting bond, they provide significant benefits to buildings—and builders—who use them.

The seasonal movement of wood is a challenge that needs to be taken into account by contractors, designers, architects and millworkers. Mortise and tenon joints are powerful enough to mitigate this movement, keeping frames and their attached parts flush and true for long periods of time, as an Eisenhardt Mills craftsman repairing a pair of historic church doors recently found.

Constructed in 1819, the doors were assembled without any glue, joined solely by a draw-bored mortise and tenon. This method involves drilling slightly off-center holes for a perpendicular peg, so that when the peg is inserted the joint draws together tightly. For almost 200 years, the doors had withstood the elements, from sun to snowstorms and everything in between, and were just as strong now as they were in 1819.

The ability to remain flush and true over lengthy periods of time also helps prevent the telegraphing of the stile and rail intersection through the paint and finish, resulting in fewer trips back to the site for the general contractor touching up painted finishes.

Traditional methods meet modern ingenuity at Eisenhardt MillsMortise and tenon joints are strong and tight enough to lessen the telegraphing of the intersection of joined pieces such as this true divided light muntin bar.

The mortise and tenon joint has remained a preferred method for millennia. While more labor intensive—and therefore more costly—than many other types of joints, it has no equal in durability. Modern methods of fastening all have their place, but more often than not, Eisenhardt Mills’ commitment to crafting the highest quality custom millwork leads to the same choice made by the Pharaohs: the mortise and tenon joint.

Photo Gallery

Traditional methods meet modern ingenuity at Eisenhardt MillsA coped walnut three step mortise and tenon joint shows the joint’s ability to create a strong and tight connection.

Traditional methods meet modern ingenuity at Eisenhardt MillsOnce assembled, the mortise and tenon joint can endure the rigors of time and pressure.

Traditional methods meet modern ingenuity at Eisenhardt MillsMortise and tenon joints are also used for muntin bars.

Traditional methods meet modern ingenuity at Eisenhardt MillsAssembled, the muntin bars will stay flush and true over prolonged periods of time, lessening the telegraphing of the intersection through painted finishes.