How to Fit a Mortice Deadlock

Last Updated: September 29, 2021

A mortice (mortise) deadlock is a strong form of lock that is embedded within a cut-out pocket space inside the door (or furniture) structure, as well as having external components. If you want to fit one yourself, you'll need to be capable of woodworking as well as using the tools required to fit the lock.

Part 1

Part 1 of 2:

Taking Accurate Measurements

1
Measure where the lock will fit on the door. As a guide, the height of your lock should be about 1 metre high.
2
Using your measurement, mark out both the top and bottom of the latch.

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3
Measure and mark out a vertical central line. This will be your guide when drilling.
4
Place a wedge under the door to prevent it from moving while you work.
5
Use some tape to mark the depth of your lock on a 19mm augur drill bit.

Part 2

Part 2 of 2:

Installing the Lock and Striker Plate

1
Starting from the top, make a series of holes. These will form the slot the lock will fit into.
2
Use a chisel to smooth the sides of the slot and clean away any excess wood so that the lock will fit easily.
3
Once the space is ready sit the lock case in, add the cover plate, and draw around all four edges. These lines mark the edges of the recess you'll need for the lock to sit flush with the door.
4
Using a hammer and chisel, make a series of cuts along all four edges. Follow this by making a series of cuts down the centre.
5
Carefully ease out the excess to form an indent.
6
Hold the lock against the door and mark the keyhole with a pencil. Use a bradawl if a pencil is too wide. Don't forget to mark both sides, as drilling from each side will prevent the wood from splitting.
7
Using a smaller drill bit than before (preferably a 9mm auger drill bit), drill two holes one above the other.
8
Use a chisel to "stitch" them together. This will form the keyhole.
9
Clean out any debris and push the lock into the slot. If it's a bit tight, give it a gentle tap with a hammer.
10
Attach the cover plate and use a drill bit smaller than the screws, to create two pilot holes. This will ensure that your screws do not split the wood.
11
Fit the keyhole covers on both sides around the keyhole space. Drill pilot holes for the screws and then attach.
12
Make sure the deadbolt works properly. Use the extended deadbolt to mark the door frame. This will show you where the strike plate needs to go.
13
Use these measurements to square the marks across the door casing.
14
Match the strike plate to your measurements and mark around all four edges.
15
Mark exactly where the deadbolt will sit.
16
Use a 19mm augur drill bit to drill two holes. This will form the recess the deadbolt will fit into.
17
Make a shallow recess for the strike plate with a hammer and chisel, just as you did on the door itself.
18
Make sure the strike plate sits flush and then pre-drill the pilot holes before attaching with screws.
19
Finally, check that the door closes and locks. If so, the job is complete.

Community Q&A

Question

I have chiseled out too much wood when fitting a deadlock so that there only one screw hole (the bottom one) can be used. Is there some sort of filler that I can screw into that I can use?

Ronan Allen

Community Answer

Cut a piece of wood to fit where you took too much, then use a good wood glue to secure it in place. Then use a screw that will go through the wood and into the wood of the door. (The screw may have to be longer than the one supplied.)