Fitting a New LockEnsuring the doors in your home have adequate locks is a very worthwhile DIY task, which offers invaluable peace of mind. The police report that the majority of burglars are opportunists who in many cases walk straight into people’s homes via inadequately secured or even open doors.

One of the best lines of defense is to fit a mortise deadlock which can be locked from both sides. You can only open a mortise deadlock with a key so if a burglar smashes a nearby glass panel he cannot open the door from inside. Importantly, mortise deadlocks also ensure, that if burglars gain access into your home via a window, they cannot escape easily through your front door.

Remember, door locks are all about home security so do not delay replacing damaged or inadequate locks on your front and back door. Read on to find out how.

Be Prepared

Fitting a new mortise door lock is a simple enough job, but it does require precision and patience. Your local DIY store should offer a good range of mortise locks of different sizes and styles which will come with instructions. You can buy a pack with everything you need or buy items such as the handle, plate and mechanism separately.

lock1 The lock packaging will normally indicate the thickness of the door it is intended to fit into. Ensure you have measured your door width and any panels on the door so it can be correctly fitted. Check whether it is the correct size for your door including whether the spindle will fit. The spindle may need to be cut to fit so that both handles fit flat onto the door but make sure it is long enough to begin with.

Have a good look at a working mechanism if you can, to help you understand how everything fits together. Ideally, your mortise lock should be fitted a third of the way from the bottom of your door.

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Useful Tools


  • Chisel
  • Screwdriver
  • Drill
  • Hacksaw
  • Pad saw
  • Ruler
  • Tape Measure
  • Pencil
  • Hammer or mallet

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Step By Step


  • The major rule to remember when getting started is to try and think of how everything fits in advance. This way you will prevent problems occurring during the fit. Every part of the mechanism needs to be clearly marked around the door before you start making holes in your door. 20px break lock5
  • Decide on height for your lock. If in doubt, check other door handles and locks for ideas. You may wish them to be consistent around your home.
  • Check the latch position. Ensure curved part of latch will strike door frame first when door is closed. 20px break lock4
  • Position the mortise lock body against side of door and mark top and bottom around the door edge and keyhole, latch and spindle positions
  • Drill spindle and key holes. Cut out the shape using pad saw. 20px break  lock3
  • Drill holes into door edge for mortise lock body. Chisel out desired shape.
  • Fit the lock and check the positions of the door handle, spindle and key hole
  • Fit the lock securely using solid screws
  • Fit the door handle spindle and fit the door handles 20px break
  • Twist the lock into locked position and close the door lock2
  • Mark the positions of the door latch and the lock bolt
  • Check the plate fits the marked positions for the holes
  • Cut out the holes in the door frame to take the catch and bolt. Take into account the door shutting into the frame.
  • Use a chisel to cut out a recess in the door frame for the plate >
  • Screw the striker plate to the side of the door 20px break

Choosing Screws

Always use solid screws when fitting a door lock and make sure they are not too long. You don’t want them protruding through the door or colliding with the screws on the opposite side of the door. Make sure your screws match the style of the lock plate and handle, i.e. you will probably want brass screws if you have a brass plate or handle.

Insurance Benefits

The extra good news is that by fitting British standard mortise locks you could also save money on your insurance premium. If you install a British Standard five lever mortise deadlock a third of the way up your door your insurer should offer you a better price. Most insurance companies are happy with a mortise lock Kite marked to British Standard BS3621. If in doubt, check with your insurer first.