Mortise sash locks fit into a large rectangular pocket cut into the edge of a door, and are most commonly seen on front and back doors. They have a dual function as a deadbolt and a knob or handle to open the door.
How does it work?
The latch on the mortise sash locks means the door stays shut without having to lock it, but the deadbolt feature is available when needed by locking the door with the key, from either side of the door. The knob or handle is used to open the door.
Parts of a mortise lock
• Lock body - fits in the door and includes the working parts of the lock.
• Lock trim - handles, levers, or pulls used to open the door.
• Strike Plate – also known as a box keep, lines the section where the lock goes. The opening in the plate is where the deadbolt slides when the door is locked.
• Keyed cylinder – operates the lock function.
Benefits of a mortise lock
A mortise lock is stronger than a cylinder lock and is versatile enough for use with different handles and door knobs, and with accessories and cylinders from a variety of manufacturers. A combination often found in properties is the use of warded mortise locks for interior doors and pin tumbler mortise locks for exterior doors.
The lock is classified by the number of lock cylinders it has and whether or not it has a deadbolt. A single cylinder mortise lock is usually found in residential premises and is opened with a key from the outside, and with a thumb-turn on the inside. A double cylinder mortise lock opens with a key both inside and outside. Dummy sets are used to match the active lock on a pair of double doors.
The locks can be used with the key alike or master key system. Using the key alike system with the mortise sash doors requires only one key, for all the locks.
Many case sizes and backsets are standardized allowing the interchange of parts and accessories from different manufacturers.
Choosing the right mortise lock
The locks come with different levels of security and are classified in terms of levers. The more levers a lock has, the more secure it is. Buyers should choose the one that best corresponds to the location of the door:
• Two-lever mortise sash locks
These should only ever be used on internal doors as they provide a minimum amount of security and work more as a deterrent, for example, the use of a two-lever lock on a store room to prevent entry by young children.
• Three-lever mortise sash locks
Again, these should only be used on internal doors as they provide a lower level of security. Houses sometimes have wash rooms or laundry rooms with a door leading outside, and an internal door with a sash lock can provide an extra barrier to entry.
• Five-lever mortise sash locks
Five-lever mortise locks are recommended by insurance companies and the police because they provide the highest level of security. Any door leading to the outside should always have a minimum of a five lever mortise sash lock on it.
• Six-lever sash locks
These are more often used in commercial environments like community housing. The door is unlocked from the outside with a key, but can be unlocked from the inside with a thumbturn and no key is needed. Particular important for health and safety reasons as no key is required to open the door in case of a fire or other emergency.
Check the height of the locks on other doors in the property, especially if any other doors are visible and place it at the same height for uniformity.
• Mark the position of the lock on the door.
• Place the lock against the door and mark the top and bottom, and then place a vertical mark in between these two lines, to guide the drilling.
• Select a flat drill bit slightly a fraction wider than the body of the lock to make the hole.
• Drill out the recess to the appropriate depth.
• Use a hammer to cut square edges at the top and bottom of the recess.
• Make the recess as clean a rectangle as possible
• Insert the lock and mark around the faceplate
• Remove the lock and carefully cut out the area for the faceplate to fit into.
• Mark where the holes for the key and handle should go.
• Drill the holes for the keyhole and handle.
• Drill the holes for the faceplate and keyhole covers.
• Fit everything and check the handles work and the key turns properly.
• Leave the door ´locked ‘so the bolts are protruding and rest the door against the frame.
• Mark the position of the bolts and latch
• Place the strike plate on the door frame and mark its position with the bolts in the middle.
• Chisel out a recess for the strike plate.
• Make a slighter deeper recess of the bolts and latch.
• Fix the strike plate.
Drilling Open a Mortise Lock
A shear line is created when the correct key is placed in the lock and the pin tumblers line up correctly, allowing the door to be opened. The purpose of drilling open the lock is to create an equivalent shear line.
Start drilling approximately an eighth of an inch above the keyway, using a ¼ inch drill bit. Start slowly, gradually increasing the pressure until you feel a jolt, which indicates you have drilled through a pin. Keep drilling until all the pins give way, but stop as soon as the last pin is done, so as not to damage the rest of the mechanism. After removing the remaining pins left in the chambers, a screwdriver inserted into the plug will unlock the door.