Replacing a mortice lock is not always as simple as buying another lock that looks similar. Two locks can have the same finish and key type but different case sizes, backsets or faceplates. Those small differences matter when the new lock must fit an existing timber door without unnecessary cutting.
This guide explains the measurements worth checking before ordering a replacement mortice lock for a home or business in Dundee.
First, identify the type of mortice lock
A mortice deadlock operates a bolt with a key but does not have a spring latch operated by a handle. A mortice sashlock normally combines a key-operated deadbolt with a latch and door-handle spindle. They are not direct substitutes for one another.
Look at the door edge and note whether the lock has a latch, a deadbolt, or both. Record any maker’s name, model number or standard marking visible on the forend (the metal plate on the edge of the door).
Case depth and backset are different measurements
Case depth is the distance from the front of the lock’s forend to the back of its metal case. It helps determine whether the lock body will fit the pocket already cut into the door.
Backset is the distance from the front of the forend to the centre of the keyhole or, for a sashlock, the handle spindle. Do not assume two locks with the same case depth have the same backset.
For an accurate match, measure the existing lock rather than relying on a generic product photograph. If the lock cannot be removed safely, a locksmith can inspect it.
Check the forend and the position of the fittings
The forend is the visible metal faceplate on the door edge. Note its height, width, screw positions and finish. A replacement with a different plate may leave gaps or require work to the door edge.
For sashlocks, check the spacing between the handle spindle and keyhole. The new lock also needs to line up with the existing handles and escutcheons. On the door frame, the keep or strike plate must match the position and travel of the latch and bolt.
What about five-lever and British Standard locks?
Lever count alone does not tell you whether a lock meets a particular security standard. If you need a British Standard mortice lock, check the exact product’s markings and specification, such as BS 3621 where applicable. Your insurer may have specific requirements for external doors, so check your policy before choosing a replacement.
Do not assume that a higher-security lock will fit the same cut-out as an older model. A change in case size, bolt position or forend dimensions can affect the fitting work.
What photographs help with a replacement quote?
- A clear photograph of the full door edge showing the lock’s forend.
- A close-up of any brand, model or standard markings.
- Photographs of the lock and handle positions from both sides of the door.
- Measurements of the forend, case depth and backset, if these can be obtained safely.
- A short description of the fault: key sticking, bolt not throwing, handle not returning, or a straightforward replacement.
If a lock has failed while the door is shut, avoid forcing the key or handle. That can make the damage worse. On fire doors or doors serving as an escape route, lock selection and fitting should preserve the door’s safety function.
Mortice lock replacement in Dundee
Locksmith Dundee Ltd can assess mortice lock repairs and replacements, including cases where an older lock is difficult to match. See our door lock replacement service, or read our related guide to replacing a nightlatch and mortice lock.
For advice or to arrange a visit in Dundee and surrounding service areas, call 01382 671054. Our business address is 64 Albert Street, Dundee. We can confirm suitable replacement options after checking the existing lock and door.