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By Amy Hanlon on 07 Jun 2023

What Are Mortise and Tenon Doors?


If you’re a savvy shed buyer, you may have noticed this term popping up as you look at sheds. Mortise and tenon is a type of carpentry joint that joins two pieces of wood together at right angles. M&T doors and windows use these joints.

Mortise and tenon doors and windows may be included in the specification of a shed, but sometimes they are additional extras.

Are they worth the additional cost?

What do they add to your shed?

At Gillies & Mackay mortise and tenon doors are available on sheds as an optional upgrade.

Why Use Mortise and Tenon Doors On A Shed?

These doors are absolutely solid, which is great news for the security of your shed

Mortise and tenon joints are among the most sturdy, long-lasting carpentry joints, which is why joiners have been using them for centuries to create everything from cabinets to bedframes to shed doors!

The five-lever mortise locks we use on our shed doors are insurance-approved. In other words, if you use one of these locks your insurance company will be satisfied that you’ve done your best to secure your shed and will pay out if anyone breaks in. 

The additional cost of these doors reflects the time, skill and experience needed to build them, but we’d recommend this upgrade. It’ll keep your shed safe for decades to come!

Now I’m no joiner, but fortunately Gordon, our workshop gaffer, has been making mortise and tenon doors since I was just a wee thing, and he was good enough to let me see exactly how they’re made.

Let’s start with the basics. 

Here you can see a mortise and tenon joint ready to be assembled. 

The tenon is the wooden slot that fits into the mortice, which is a hollowed-out rectangle in the second piece of timber. When the tenon slots into the mortice, a right-angled joint is made.

This particular joint also features a “horn”, where timber slightly longer than the door frame is used, This gives the door more integrity as the joint isn’t exposed to air or the elements. The horn also prevents splitting when the mortise is cut. The pencil line on this diagram shows where the doorframe will end, half a centimetre or so from the joint itself. The extra timber is the horn.

As you can see from this picture, each part of the joint has to be made correctly in order for everything to fit together. This is highly skilled work. 

How are Mortise and Tenon joints made?

You can cut these joints by hand, but given the sheer volume of doors and windows that G&M need, we use machinery. 

When we built summerhouses, our workshop shut down for six weeks over the winter to create all the doors and windows we needed for a whole season’s worth of summerhouses. A typical stock build involved 440 summerhouse doors, with one mortise and tenon joint each. 

As for the windows? Just don’t ask. Each one of those 220 summerhouses had at least four windows, with some models sporting as many as six. Each window had a mortise and tenon joint in its middle bar. That’s more mortise and tenon joints than anyone in the universe wants to look at for six straight weeks. 

So let’s see how it’s done. 

Mortice and Tenon: making the frame of the door.

Here are the five pieces of timber that make up the frame of the door. You can see the six mortises have been cut out of the long posts, and you can see the tenons on the horizontal struts. 

Each mortise is glued, then the tenons are slotted in, and the second upright is placed on top. The door is clamped to make sure that the joints fit tightly together. 

Next, the door must be squared.  If the mortise and tenon joints aren’t precisely 90°, the door won’t hang properly, and as the timber moves the door may stick or fail to close. 

Gordon does this by measuring the diagonals of the door and making sure that they are exactly the same length. This means some adjustments to the frame.

Once the door is square and all the measurements are accurate, the mortise and tenon joints are reinforced with nails.

Then, a router is used on the inside frame of the door to round off the edges.

Next, it’s time for the hinges. First, the door is placed on its side, and then a router is used to cut out the inserts for the hinges

Then, wood filler is used to cover the nail dents, and to fill any knots in the wood.

Once this has been done, it’s time to remove the horns from the doorframe.

Adding the weatherboard.

With a completed frame, it’s time to add weatherboard to make this a seriously solid shed door.

To make sure that the weatherboard is weatherproof, Gordon applies a layer of silicon to the rebate in the frame that will hold the weatherboard.

The 19mm tongue-and-groove weatherboard fits into this rebated channel in the frame. Each board slots into the previous one, creating a water-resistant wall of wood.

Gordon covers the frame with weatherboard until he reaches the second-to-last piece.

This gap isn’t wide enough for a full board, so Gordon measures and trims a board to fit.

Perfect! To make sure that the weatherboard fits snugly, Gordon adjusts this panel until the weatherboard is completely square. He measures the panel to make sure that every board is exactly correct.

Once this job is done, the weatherboard is nailed to the frame.

Inserting the lock.

Next up, the lock! The frame has already been machined to hold the lock correctly, as you can see here:

Gordon checks the lock and adjusts it for the opening direction of the door.

He then inserts the lock into its pre-machined slot

Adding the braces.

For the final step, bracing timbers will be attached diagonally to the finished door to keep it square and prevent warping.

Once this has been done, the hinges will be added, and the door will receive its base coat of paint, all set to secure a brand-new shed. 

You can see our M&T doors in action at our Show Area here in Errol. Pop over for a visit and take a good look!

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