An Introduction to Mortise Locks

A mortise lock is a type of lockset that is installed by cutting a pocket into the side of a door.  Before mortise locks became widely available in the late nineteenth century, most door locks were surface mounted, and typically would consist of a cast iron box bolted to the inside of the door with a hole for the key to be inserted through.  This can be unsightly and many surface mounted locks were handed, meaning that you would have to specify the type of door you had when you purchased a lock.  Today surface mounted locks still exist in the form of some panic hardware and interlocking deadbolts.

This Sargent & Greenleaf lever tumbler lock is the oldest lock in my collection.  It was most likely produced in the late nineteenth century right here in Rochester

Then came mortise locks.  Installing the lockset inside a cavity in the door allowed for a more aesthetic appearance and provided better security against forcible entry.  Although some mortise locks were handed, the handing could usually be reversed by opening up the box and flipping the latch and spindle hub around (if it uses a swivel spindle).  On newer mortise locks, the handing can be reversed without even having to open up the box.  This made for a more secure and more versatile lockset.  Most mortise locks should be installed on doors that are at least 1 3/4" thick.

Mortise locks come in many shapes and sizes.  Some mortise locks accept a warded bit key.  Bit key mortise locks are common on the interior doors of many homes within the city of Rochester.  Mortise locks that use a cylinder key may be found on the exterior doors of some older homes.  Today most mortise locks are built to fit inside an ANSI Type 86 mortise pocket.  This is the standard pocket that is usually mortised into a door at the factory (if you're ordering a fire-labeled door it has to be mortised at the factory to retain its fire rating).  The customer may then install whatever brand of lock they prefer.  Originally different lock manufacturers produced mortise locks in different dimensions, so it may be difficult to find a replacement mortise lock for an older door.

Many mortise locks feature two buttons located on the faceplate either above or below the latch.  These buttons are called the stopworks.  Pushing one of these buttons will lock the outside knob or thumb piece.  Pushing the other button will unlock the outside knob or thumb piece.  The user may then use their key to retract the latch and enter, or they may exit by simply rotating the inside knob, which is always unlocked.

This Corbin mortise lock features both a latch and a deadbolt, which are unlocked by the same cylinder.  This lock is not interconnected, so the deadbolt must be retracted using the inside thumb turn before someone can get out.

Another advantage of many mortise locks is that the latch and deadbolt are usually contained in a single unit.  On many newer mortise locks, they are also interconnected.  This means that rotating the inside handle will retract both the deadbolt and the latch.  This is especially useful from a life-safety standpoint, as it allows a person to exit by only rotating the inside handle.  The person does not have to fumble with a thumb turn to retract a deadbolt and then twist the handle to get out.

Today mortise locks are less common, largely due to hardware and labor costs when compared to cylindrical locksets.  However in some commercial construction and applications requiring a robust lockset with longevity, mortise locks are still popular.  Ultimately it comes down to whether the customer is looking for reliability over time or a lockset that is more affordable and relatively easy to install by comparison.