A mortice latch is a lock case let into the edge of a door that is operated only by the handle: it contains a sprung latch bolt and no deadbolt, so the door cannot be locked. Push the handle down, the sloping latch retracts and the door opens — that is the whole mechanism. In Dutch this type of lock is called a loopslot.
Where is it used?
- Internal doors in houses: living room, hallway, kitchen, utility room
- Cupboard doors and meter cupboard doors
- Doors in offices and commercial buildings where locking is deliberately not wanted
- Doors on an escape route, where accidental locking would be a hazard
For a bathroom or WC you would use a bathroom lock with a thumbturn and emergency release instead, for a bedroom a sashlock with a deadbolt, and for an external door always a tested security lock.
Recognising it and getting the sizes right
The forend tells you immediately: a mortice latch has one opening for the sloping latch and one spindle hole, but no keyhole, no cylinder hole and no second rectangular opening for a bolt.
Key dimensions when replacing one:
- Backset — the distance from the face of the forend to the centre of the spindle hole; common UK sizes are 44 mm and 57 mm (sold as 2.5 and 3 inch cases)
- Case size — the overall length of the lock body, which must fit the existing mortice
- Forend — width and shape (square or radiused) must match the existing rebate
- Spindle — usually 8 mm square
Replacing one step by step
- Undo the handles and slide out the spindle
- Remove the two screws in the forend
- Ease the lock case out of the mortice with a screwdriver
- Measure the backset, handle height and forend size on the old lock
- Slide the new lock in, screw it back, refit the spindle and handles
- Check that the latch drops cleanly into the striking plate; if the door has dropped, move the striking plate rather than filing the latch
> Note: fit the latch so that the sloping face points towards the frame the door closes against. On almost every latch you can pull the bolt out and refit it turned through 180 degrees.
Related terms
- Internal door
- Ironmongery
- Backset
- Window frame
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