Mortice Deadlocks — Simple Security for the Right Doors (DIN & UK)
- FDH Team
- Sep 21
- 6 min read
Who this is for: Joiners, fitters, manufacturers, and anyone choosing ironmongery for timber fire doors.
---
What is a (mortice) deadlock?
A deadlock is a morticed lock-case with only a deadbolt—no sprung latch and no handle follower. You turn a key (or a thumbturn if fitted with a suitable cylinder) to project a solid bolt into the keep. That’s it: locked or unlocked.
Because there is no latch, a deadlock doesn’t keep a door closed in day-to-day use. It’s a secure “parked” position for doors that are normally kept locked, or as an additional lock to supplement a latch-based lock.
Where deadlocks make sense (and where they don’t)
Good applications
Store rooms / comms cupboards / risers that are normally locked shut.
Secondary security on external doors (often paired with a sash lock or night latch).
Plant rooms or cleaner’s cupboards where key control matters.
Flush inspection hatches (when a mortice solution is required and tested for the door/hatch).
Use with caution or avoid
Doors on escape routes (you must not require a key to get out; use thumbturns or certified escape hardware as appropriate).
Everyday traffic doors that need to self-latch—a deadlock alone will not hold against fire/pressure. For most fire doors in regular use you’ll want a latch (e.g., a sash lock or latch lock) plus a self-closer.
Apartment entrance doors typically require keyless egress from inside and a latching action—these are rarely suitable for deadlock-only setups.
Rule of thumb: If people pass through it daily, you almost certainly need a latch. If it’s usually locked and only opened by authorised staff, a deadlock can be ideal—provided the door assembly is tested for it.
Anatomy of a deadlock (DIN & UK patterns)
Lockcase: Morticed into the door edge. DIN-pattern cases follow standardised case sizes for predictable prep.
Deadbolt: Solid steel (often with anti-saw inserts on security models). Typical throw ~20 mm (varies by model).
Forend/strike (keep): Plate on the door edge and a matching keep in the frame; must be flush and well-seated.
Cylinder (if euro profile): Many deadlocks take euro profile cylinders; others are built as lever deadlocks (traditional 3/5-lever).
Escutcheons / turns: Tidy the cylinder/lever aperture and protect the door skin. On fire doors, use intumescent kits where required by test evidence.
Common patterns you’ll see:
DIN euro deadlock (no follower, euro cylinder only).
UK lever deadlock (3- or 5-lever).
Narrow-stile deadlocks for slim sections (less common on timber fire doors).
Standards & fire-door notes (plain English)
Locks: Look for products assessed to EN 12209 (mechanical locks) and bearing UKCA/CE where applicable.
Cylinders: EN 1303 classification; optional security marks like TS 007 for domestic security.
Fire performance: The door assembly is what’s fire-tested. Use **locks and cylinders that appear on the door manufacturer’s approved hardware list (or the doorset’s test evidence). Fit any intumescent kits specified by the lock/door maker.
Exit/egress: For doors people might need to escape through, you must ensure keyless egress (e.g., internal thumbturn) or certified escape hardware (EN 179/1125), depending on the door’s role.
FDH disclaimer: This is a practical summary, not a legal substitute for standards or test evidence. Always follow the door manufacturer’s guidance and official standards.
Choosing the right type of deadlock
1) Cylinder type
Euro cylinder deadlock: Flexible, re-keyable, access control friendly.
Lever deadlock: All-in-one case; simple, no separate cylinder.
Tip: Where you need master-keying or easy re-coring, go euro cylinder.
2) Inside operation (egress)
Key/key (both sides keyed) — higher security but not for escape routes.
Key/turn (thumbturn inside) — allows keyless egress; safer where people might be inside.
3) Security & environment
Security grade: Choose higher grades for external doors.
Corrosion resistance: Plant/boiler rooms may need better finishes.
Fire rating: Ensure the lock and cylinder are approved for the FD rating of the door (e.g., FD30/FD60) with the correct intumescent.
4) Dimensions that matter
Backset (centre of keyway/cylinder to face of forend). DIN patterns are consistent; non-DIN vary—match to your prep.
Case height/width & forend size: Must align with the door’s permitted cut-out.
Bolt throw: Check manufacturer data; many specifiers like ~20 mm+ for security.
Fitting guide (joiner’s checklist)
1. Confirm approval: Check the door manufacturer’s hardware list for the exact model, cylinder type, and any intumescent kit requirements.
2. Mark out accurately: Use manufacturer templates. Keep edge distances and clearances within instructions.
3. Cut the mortice cleanly: Square corners, no breakout. Maintain minimum door core around the case (don’t over-widen the pocket).
4. Fit intumescent (if specified): Around the case and/or under the forend/keep. Don’t substitute materials or thicknesses.
5. Install case & forend: Forend flush with the edge; secure with the supplied screws (or specified type).
6. Cylinder & escutcheons: Correct cylinder length (flush or just proud of escutcheon). Use through-bolts where provided; add intumescent pads if required.
7. Keep & frame prep: Position to achieve full bolt throw without binding. Seat the keep on a solid packer; avoid crushing intumescent seals.
8. Test operation: Key/turn should drive smoothly, bolt should fully engage. No rattle; no partial throws.
9. Sign-off: Record model codes, batch, and fire rating in your job sheet. Photograph before/after if your QA requires.
Maintenance & inspection (what to check)
Smooth key/turn action with full throw; no stiffness.
Fixings tight (case, escutcheons, keep).
Cylinders undamaged, correct length, no wobble.
Intumescent present and intact where required.
Frame keep alignment—bolt should hit the pocket centre and seat fully.
Door performance overall: If the door is in use, ensure a closer + latch elsewhere keeps it shut under its normal duty; don’t rely on a deadlock for day-to-day closure.
Maintenance frequency depends on traffic and environment; many sites adopt quarterly checks for low-traffic service doors and monthly for higher-risk areas.
Common site mistakes (and quick fixes)
1. Deadlock used as the only means of closure on a busy door
Fix: Swap to a sash lock (or latch + closer) and keep the deadlock as secondary, if both are permitted by the door’s evidence.
2. Cylinder too long or too short
Fix: Re-size. Aim for cylinders that finish flush or slightly proud of the escutcheon.
3. Missing intumescent
Fix: Fit the exact kit stated by the lock/door maker. Don’t improvise.
4. Keep floating in a hollow frame
Fix: Solid backing packer and the correct screws. The bolt must drive into solid material.
5. Binding bolt / partial throw
Fix: Re-align the keep. Check door margins and any frame movement.
6. Keyed both sides on an escape route
Fix: Change to key/turn or certified escape hardware to ensure keyless egress.
Deadlock vs. Sash lock vs. Latch lock (at a glance)
Feature Deadlock Sash lock Latch lock
Holds door closed without locking ❌ ✅ (Latch) ✅(Latch)
Needs handle furniture ❌ ✅ ✅
Best for normally-locked rooms ✅ ⚠️ (When Traffic Exists) ❌
Suitable as secondary security ✅ ⚠️ ❌
Typical fire door in regular use ❌ (Deadlock Alone) ✅ ✅ (With Closer)
Takeaway: Deadlocks are great at being locked. Sash/latch locks are great at being closed.
---
Spec sheet helper (copy/paste)
Use this to brief your supplier:
Name: Mortice Deadlock, Euro Profile, DIN Pattern
Category: Locks – Deadlocks
Manufacturer: [Brand]
Model Code: [Code]
Fire Rating: Suitable for FD30/FD60 when installed to test evidence with specified intumescent kit
Certifications: EN 12209; UKCA/CE (as applicable); Cylinder to EN 1303 (if euro)
Material Type: Steel lockcase; [finish/forend type]
Finish Options: Satin stainless / PVD brass / [others]
Description: DIN-pattern mortice deadlock with ~20 mm bolt throw, euro cylinder, for timber doors. Use as a normally-locked solution or as secondary security. Not a substitute for a latching action on traffic doors.
Product Image: [link or file]
---
Quick procurement checklist
[ ] Model appears on the door’s approved list (or is evidenced as compatible).
[ ] Fire kit (intumescent) included/ordered.
[ ] Cylinder format (key/key or key/turn) confirmed to the fire/egress plan.
[ ] Correct backset and case size for your prep.
[ ] Keep type and fixings suited to the frame construction.
[ ] Escutcheons/rose sets compatible; through-bolt options if needed.
[ ] Finish and corrosion resistance appropriate for the environment.
---
FAQs
Do I need a closer if I use a deadlock?
If it’s a fire door, you almost always need a self-closing device. A deadlock doesn’t close the door; it only locks it.
Can I fit a deadlock on a communal escape door?
Not as the only locking; escape doors typically require keyless egress and certified escape hardware. Use a thumbturn or panic/escape device as dictated by the fire strategy.
Is a lever (5-lever) deadlock better than a euro deadlock?
Different tools. Euro cylinders give you master-keying and easy re-coring. Lever deadlocks are simple and robust. Choose based on the building’s key control needs and the door’s evidence.
Do I always need intumescent around the lock?
Follow the lock and door manufacturer’s instructions. Many fire-tested door-sets do require specific intumescent kits for the lock and sometimes the cylinder/escutcheon.
Comments