Choosing a lock for a glass door
Why a standard mortice lock cannot go into a glass leaf, what a patch fitting changes, and the measurements to take before anybody quotes.
Choosing a lock5 min read
A glass door is the one case where the usual advice stops applying. Most access hardware assumes a timber or metal leaf with a pocket cut into its edge, and a glass leaf has no edge to cut into.
Why the standard answer does not fit
A mortice lock needs a mortise — a rectangular pocket machined into the door's edge, deep enough to take the lock body. Toughened glass cannot be machined after it is made. Every hole and cut-out in a glass leaf is done before toughening, at the factory, and a toughened panel that is drilled afterwards does not get a neat hole; it fails.
If a supplier offers to drill your existing toughened door on site, that is the moment to stop. The panel is not repairable and it is not modifiable.
What a patch fitting does instead
A glass door lock clamps. The hardware grips the leaf above and below with a patch, and the locking mechanism lives inside that patch rather than inside the glass. The bolt then throws into the floor, into the frame, or into the matching patch on a second leaf, depending on the opening.
That changes what you need to know before anybody can quote. On a timber door the questions are about the door. On a glass door they are about the opening.
What to measure first
- The glass thickness, usually 10mm or 12mm — it decides the patch.
- Whether the leaf already has cut-outs, and where. Existing cut-outs constrain the hardware to what fits them.
- Whether the door is single or double, and which leaf is the active one.
- What the bolt can throw into: a floor socket, the frame, or the other leaf.
- Whether there is a floor spring, and its make. It shares the bottom patch's space.
A photograph of the full opening, taken square on from a few steps back, answers most of these faster than a tape measure does. Include the floor and the head of the frame in the shot.
The case for replacing the leaf
Sometimes the honest answer is that the existing panel cannot take the hardware you want, and a new leaf with the right factory cut-outs is cheaper than working around the old one. That is not an upsell; it is the consequence of toughened glass being finished before it arrives.
Ask for both options priced. If only one comes back, ask why the other was ruled out.
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