How do I fit a bathroom lock or a privacy bolt?

A bathroom lock is the one lock in the house designed to be defeated. Its job is privacy, not security, and every design includes a deliberate way in from outside. Choosing and fitting one is straightforward; the part people skip is testing the release, and that is the part that matters.

Safety

What you'll need

• A bathroom mortice lock or a privacy bolt set
• A marking gauge, try square and marking knife
• Drill with a bit matching the case thickness
• Sharp chisels
• A depth stop or tape

Step by step

1. Choose the arrangement.A bathroom mortice sashlock combines a latch and a privacy bolt in one case, worked by a handle and a thumbturn, and is the neatest solution on a door that needs a handle anyway. A separate privacy bolt above or below the existing latch suits a door that already has a latch you are keeping.
2. Check the door will take it.Solid or solid-core timber only for a mortice type. On a hollow-core door, the lock has to sit within the lock block, and a separate surface-mounted or shallow bolt is often the practical answer.
3. Position it clear of the latch.A privacy bolt goes far enough from the existing latch that neither mortice weakens the same piece of timber. Above the handle is conventional and it is easy to reach.
4. Mark from both faces.Gauge the mortice from both faces of the door so it is genuinely central, exactly as for any mortice lock. An off-centre bathroom bolt splits a stile just as readily as an off-centre deadlock.
5. Drill and chop the mortice.Overlapping holes to a set depth, then pare square with a chisel. Test-fit frequently. The case must slide in without force and the forend must finish flush.
6. Drill the spindle holes for the turn and the release.From both faces to a meeting point, using the lock itself as the template once it is in the mortice. The inside gets the thumbturn spindle; the outside gets the release, which on most designs is a slotted spindle taking a coin or a screwdriver.
7. Cut the forend recess.Knife round the faceplate with the lock fully home, remove it, pare the recess so the plate sits flush. Fix with two screws.
8. Fit the turn and the release and test the emergency function first.Before the door is ever closed on it: throw the bolt from inside, then release it from outside with a coin. Do it several times. If it is stiff or ambiguous, sort it now.
9. Mark and cut the keep.Close the door and mark where the bolt lands, using chalk or lipstick on the bolt end. Cut a mortice in the frame deep enough that the bolt never bottoms out, then recess the keep plate flush.
10. Check with the door closed and someone outside.Lock it from inside, have someone open it from outside with a coin, twice. Then tell everyone in the house where the release is and what opens it.
11. Add the vacant/engaged indicator if you fitted one.Indicator bolts show red or green on the outside. They are worth it on a shared bathroom, and they are fitted the same way with an extra spindle.

Common mistakes

• Fitting a standard sashlock to a bathroom — It needs a key from inside, which means the key lives in the lock, which means it cannot be operated from outside in an emergency. Bathroom locks exist as a distinct product for exactly this reason.
• Never testing the release — A release that is stiff, painted over or fouled by a badly fitted spindle is discovered at the worst possible moment. Test it on the day you fit it and again after decorating.
• Fitting a surface bolt on a child's bathroom door — Most surface bolts have no external release at all. If the door has to be lockable and a child uses it, the lock must have a release.

Questions people ask