Repairing Old Latches

An older interior or exterior door, and some newer high-end exterior doors, may have a mortise latch. These fit into rectangular holes (mortises) in the edge of the door. In many cases the mortise latch assembly includes a key-operated dead bolt.

If the latch does not operate smoothly, scrape away any paint buildup. (The latch itself should not be painted, though it often is.) Dig out any debris that may be holding the latch bolt. Spray a bit of graphite or silicone lubricant around the latch bolt. If these measures do not work, remove the unit and inspect it.

Repair parts or a replacement unit may not be available at a hardware store or home center. Renovation supply dealers and locksmiths may have them, or you can search Internet sources.

Prestart Checklist

Time
Less than an hour for repairs, but finding replacement parts may be difficult

Tools
Screwdriver, pliers, vacuum or canned air

Skills
Some mechanical aptitude

Prep
Place a drop cloth on the floor below the door.

Materials
Spray lubricant, replacement parts as needed

To remove a mortise lock, remove both knobs and the shaft. (Usually you loosen a setscrew on one of the knobs, then pull it off. Some knobs screw onto the shaft.) Remove the two lock retaining screws and pry the mortise latch out.

Place the latch on a worktable. Unscrew one or two screws and carefully remove the cover. Study the parts and how they go together so you can replace them correctly.

If you see a broken part -- usually a spring or an arm that connects to the latch bolt -- remove it and try to find a replacement part. It may be easier to buy a whole new unit.

Vacuum away dust or clean the lock with canned air. Lightly spray with silicone lubricant or graphite (not oil; it gums up), then replace the cover. Test and then reinstall the lock.