A mortise lock (also spelled mortice lock in British English) is a lock that requires a pocket—the mortise—to be cut into the edge of the door or piece of furniture into which the lock is to be fitted. In most parts of the world, mortise locks are found on older buildings constructed before the advent of bored cylindrical locks, but they have recently become more common in commercial and upmarket residential construction in the United States. The design is widely used in domestic properties of all vintages in Europe.
Mortise locks have been used as part of door hardware systems in the US since the second quarter of the eighteenth century. In these early forms, the mortise lock mechanism was combined with a pull to open the unlocked door. Eventually, pulls were replaced by knobs.
Until the mid-nineteenth century, mortise locks were only used in the most formal rooms in the most expensive houses. Other rooms used box locks or rim locks; in contrast with embedded mortise locks, the latch itself is in a self-contained unit that is attached to the surface of the door. Rim locks have been used in the United States since the early eighteenth century.
An early example of the use of mortise locks in conjunction with rim locks within one house exists at Thomas Jefferson's Monticello. In 1805, Jefferson wrote to his joiner listing the locks he required for his home. While closets received rim locks, Jefferson ordered 26 mortise locks for use in the principal rooms.
Depictions of available mortise lock hardware, including not only lock mechanisms themselves but also escutcheon plates and door pulls, were widely available in the early nineteenth century in trade catalogues. However, the locks were still expensive and difficult to obtain at this time. Jefferson ordered his locks from Paris. Similarly, mortise locks were used in primary rooms in 1819 at Decatur House in Washington, DC while rim locks were used in closets and other secondary spaces.
The mortise locks used at Monticello were warded locks. The term "warded lock" refers to the lock mechanism, while the term "mortise lock" refers to the bolt location. Warded locks contain a series of static obstructions, or wards, within the lock box; only a key with cutouts to match the obstructions will be able to turn freely in the lock and open the latch.
Warded locks were used in Europe throughout the medieval period and up until early 19th century. Three English locksmiths, Robert Barron, Joseph Bramah, and Jeremiah Chubb, all played a role in creating modern lever tumbler locks. Chubb's lock was patented in 1818. Again, the term refers to the lock mechanism, so a lock can be both a mortise lock and a lever tumbler lock. In the modern lever tumbler lock, the key moves a series of levers that allow the bolt to move in the door.
The next major innovation to mortise lock mechanisms came in 1865. Linus Yale, Jr.'s pin tumbler mortise cylinder lock put not only the latch or bolt itself inside the door, but also the tumblers and the bolt mechanism. Up to this point, the lock mechanism was always on the outside of the door regardless of the bolt location. This innovation allowed keys to be shorter as they no longer had to reach all the way through a door. Pin tumbler locks are still the most common kind of mortise lock used today.
Mortise locks may include a non-locking sprung latch operated by a door handle. Such a lock is termed a sash lock. A simpler form without a handle or latch is termed a dead lock. Dead locks are commonly used as a secure backup to a sprung non-deadlocking latch, usually a pin tumbler rim lock.[note 1][according to whom?]
Mortise locks have historically, and still commonly do, use lever locks as a mechanism. Older mortise locks may have used warded lock mechanisms. This has led to popular confusion, as the term "mortise lock" was usually used in reference to lever keys in traditional European terminology. In recent years the Euro cylinder lock has become common, using a pin tumbler lock in a mortise housing.
The parts included in the typical US mortise lock installation are the lock body (the part installed inside the mortise cut-out in the door); the lock trim (which may be selected from any number of designs of doorknobs, levers, handle sets and pulls); a strike plate (or box keep), which lines and reinforces the cavity in the door jamb or frame into which the bolt fits; and the keyed cylinder which operates the locking/unlocking function of the lock body.
The installation of a mortise lock can be undertaken by an average homeowner with a working knowledge of basic woodworking tools and methods. Many installation specialists such as carpenters use a dedicated mortising jig which makes precise cutting of the pocket a simple operation, but the subsequent installation of the external trim can still prove problematic if the installer is inexperienced.
Although the installation of a mortise lock actually weakens the structure of the typical timber door, the embedded lock is typically stronger and more versatile than the newer bored cylindrical lock format, both in external trim, and functionality. Whereas the newer mechanism lacks the physical volume and mechanical stability required for ornate and solid-cast knobs and levers, the mortise lock can accommodate a heavier return spring and a more substantial internal mechanism. Mortise locks are available in a wide range of functional security configurations, and are widely installed in industrial, commercial, and institutional environments.
Furthermore, a typical mortise lock typically accepts a wide range of other standardized manufacturers' cylinders and accessories, allowing architectural and functional conformity with other lock hardware already on site.
Manufacturers of mortise locks in the United States include Accurate, Arrow, Baldwin, Best, Corbin Russwin, Emtek Products, Inc, Falcon, Penn, Schlage, Sargent, and Yale. Distributors such as Nostalgic Warehouse carry a wide range of decorative trim and accessories to dress up the appearance of a lock installation. Also, many European manufacturers whose products had previously been restricted to "designer" installations have recently gained wider acceptance and use.