Mortise locks have been installed into residences and commercial buildings for more than 100 years. The basic concept of the mortise lock is a lock body that is installed into a mortised pocket within the lock edge of the door. This type of lock is concealed and to some degree protected by the exterior and interior faces of the door. The earliest mortise locks contained a built-in warded lock mechanism operated with a bit or barrel (skeleton) key. After the invention of the pin tumbler lock mechanism by Linus Yale Jr., pin tumbler mortise cylinders were incorporated into the mortise locks.
Today’s mortise locks offer a higher degree of security and functionality. These locks accommodate just about every high security lock manufacturers’ mechanisms as long as they are incorporated into a standard diameter mortise cylinder or a Mogol mortise cylinder.
From the late 19th to the mid-20th century, mortise locks were the preferred lockset, installed into most interior and exterior doors. Mortise locks are available as a lockset and as an auxiliary mortise deadbolt lock. Some interior doors might be equipped with a warded mortise lock and the exterior doors with a pin tumbler-operated mortise lock.
Interest has been high recently in the use of mortise locks because of their customizable appearance. Architects have begun to specify mortise locks for commercial and more expensive residential properties.
The mortise lock is more versatile than a cylindrical or tubular lock in functionality and trim variations. Mortise lock functionality is divided by two factors - the number of lock cylinders (0, 1, or 2) and if the lock is equipped with or without a deadbolt. Mortise locks are available with more than 50 functions including electrified functions.
Since most North American mortise locks are designed to operate with a mortise cylinder, there is not the limitation that cylindrical locks have with different size lock cylinder bodies or different configuration removable/interchangeable cores. Nor is there the exposed lock body on the interior side of the door using a rim mounted lockset.
In addition, mortise locks can be customized to enhance the customer’s decorating goals. Mortise locks can be equipped with cast knobs and levers, placed onto ornate to modern escutcheons and trim of varying sizes and shapes. For example, a two-point locking mechanism consists of a mortise lockset and mortise auxiliary lock.
Institutional mortise locksets used to control access in asylums and detention facilities require a higher level of security. In addition to heavy duty construction, institutional mortise locks can accept mogul style lock cylinders and anti-ligature knobs.
Before mortise lock size standards (ANSI/BHMA) were enacted, lock manufacturers would design and manufacture their mortise locks in the size, configuration and applications to meet their individual requirements. This meant that one manufacturer’s mortise lock, for example, one model of a Challenger Mortise Lock door prep, was not necessarily interchangeable with another manufacturers’ mortise lock or even a different Challenger Mortise Lock without some modification. The differences could include the case (body) dimensions, the front dimensions, the location of the latch and the deadbolt, and the location of the mortise cylinders and knobs. This meant that once an end user installed in specific brand mortise lockset, they were basically customers for at least the life of the door.
Sometime, you could get lucky and find a replacement mortise lock manufacturer with door prep similar to the lock you were replacing and using large enough escutcheons would cover the existing door prep and painted or finished trim edges remaining from the replaced (in most instances, an out-of-business mortise lock manufacturer).
Marks USA’s custom lock division manufactures mortise lock bodies and trim to customers’ specifications. They manufacture two mortise lock bodies, the Series 91 and Series 114. These high pressure cast Zamac body mortise locksets are designed to be direct replacements for existing exterior door mortise locks equipped with mortise cylinders.