How To Replace A Mortise Lock

If you own an older home, it likely uses a mortise lock. A mortise lock is a lock set built in the door that uses a latch and deadbolt combination. Instead of upgrading the lock, you can replace a broken or inoperable one to preserve the antiquity of your home. Here are some tips on how to replace a mortise lock.

Remove the Knobs and Shaft

For this project, you will need a utility knife, putty knife, hammer, damp cloth or can of pressurized air, silicone or graphite lubricant, a heat gun or blow dryer, and a replacement mortise lock. Remove the screw set that fastens one of the door knobs to the door shaft with the screwdriver, which should enable you to disconnect both door knobs, and pry the door shaft from the lock. If you can't get the knobs off, tap around the knob bases with the hammer to build pressure that will help loosen the knobs.

Remove the Face Plate and Lock

Mortise locks are commonly secured with a face plate, side covers, and mounting screws on the door edge. Loosen the screws in the door edge with a screwdriver to pry off the face plate and side covers. Press slightly on the upper or lower edge of the face plate with the screwdriver to disengage the lock. If the face plate has a thick layer of paint, warm the paint with a hair dryer or heat gun to soften it, then scrape it off with a putty knife. Scrape any paint inside the screw set with the screwdriver.

Install the New Lock

Wipe wood chips, dust, and debris from inside the lock hole with the damp cloth to help the new lock fit better, or use a can of pressurized air to get dust from the lock hole. Pressurized air is used to clean dust from computers and camera equipment. Lubricate the new lock mechanism with the silicone lubricant or graphite lubricant, and be certain to spray it on any area where metal comes into contact with metal.

Set the new lock in place, and make certain it aligns with the keyhole. Test the lock for proper operation by inserting the knob shaft into the hole, and trying the key on the deadbolt and latch. If it all works, reinsert the face plate, side plates, and knobs. 

Replacing a mortise lock doesn't require much skill, but it does take patience. If the lock is still inoperable or you want to upgrade, contact a locksmith.