Hollow-core doors are common throughout New Zealand homes, but their internal cardboard honeycomb structure means there's nothing solid to anchor a lockset into — unless a lock block (a solid timber insert) is fitted first. Whether you're replacing a damaged block or fitting one for the first time, this is a manageable DIY job with the right tools and a bit of patience.
What Is a Lock Block?
A lock block is a solid timber insert — typically pine or similar — glued inside a hollow-core door at the latch/lock position. It gives the lockset's latch bolt and fixing screws something solid to grip. Most new hollow-core doors come with a lock block already fitted at a standard height (usually around 900–1000 mm from the floor), but older doors or doors that have had locks moved may have a missing, damaged, or incorrectly positioned block.
Tools and Materials You'll Need
- Tape measure and pencil
- Utility knife or sharp chisel
- Jigsaw or oscillating multi-tool
- Drill with spade bits and hole saw (typically 54 mm for a standard latch)
- Timber for the lock block (solid pine, sized to fit snugly — usually around 90–100 mm wide × the door thickness minus both face skins)
- Waterproof PVA or construction adhesive (e.g. from Bunnings or Mitre 10)
- Clamps or heavy weights
- Sandpaper and filler
- Paint or stain to match (see Resene or Dulux for touch-up options)
Step 1 — Locate the Existing Lock Position
Measure and mark the centre of your new lock position on the door edge. The standard latch height in NZ is typically 900–1000 mm from the finished floor level, but check your existing hardware or the door frame rebate to confirm. Use a bradawl or thin drill bit to probe the door edge and confirm whether a lock block is already present and where it ends.
Step 2 — Open Up the Door Edge
Using a sharp utility knife and chisel, carefully remove the timber lipping (the solid edge strip) from the door edge at the lock position. Work slowly — you want a clean section you can reuse or replace. Most hollow-core doors have a 20–25 mm solid timber lipping glued along each edge. Cut only as much as you need to access the interior cavity (typically 150–200 mm is sufficient).
Step 3 — Clear the Cavity
Once the lipping is removed, use a chisel or a bent piece of wire to clear out the cardboard honeycomb from inside the cavity where your lock block will sit. You need a clean, clear space for the block to slide in and sit flush.
Step 4 — Cut and Fit the Lock Block
Cut your solid timber block to fit snugly inside the cavity. It should:
- Be the same thickness as the internal cavity (measure carefully — typically 27–32 mm for a standard 35 mm door)
- Be wide enough to extend well past the latch hole on both sides (at least 40 mm either side)
- Slide in without forcing, but with minimal gap
Do a dry fit first to confirm the block sits flush with the door face skins before applying any adhesive.
Step 5 — Glue the Block In
Apply a generous bead of waterproof PVA or construction adhesive to all contact surfaces of the block. Slide it into position, ensuring it's centred on your lock mark. Clamp the door faces together firmly (use clamps with timber offcuts to protect the door face) or weigh the door down flat and stack heavy items on top. Allow to cure as per the adhesive manufacturer's instructions — typically at least 24 hours.
Step 6 — Refit the Lipping
Glue the timber lipping back into place over the cavity opening, clamping until set. If the original lipping was damaged, cut a new piece of matching timber. Sand flush once dry.
Step 7 — Drill for the Lockset
Once the adhesive is fully cured, drill your latch hole through the door edge and the face hole(s) for the lockset body using the appropriate spade bit or hole saw. Follow the lockset manufacturer's template carefully. Most standard NZ locksets use a 54 mm face hole and a 25 mm latch hole, but always check your specific hardware.
Step 8 — Fill, Sand and Touch Up
Fill any gaps or surface damage with a suitable interior filler, sand smooth, and touch up the paint. Resene and Dulux both offer sample pots for colour matching.
Tips for a Quality Result
- Don't rush the glue cure — a block that shifts before the adhesive sets will cause problems with the lockset alignment.
- Use solid pine or similar for the block — MDF is not suitable as it doesn't hold screws well.
- If the door is a fire door (often required between a garage and living space under the NZ Building Code), check with your local council or a Licensed Building Practitioner before modifying it — fire doors have specific requirements.
- For guidance on door hardware and building standards, BRANZ and MBIE Building Performance are useful NZ references.
When to Call a Professional
This job is generally within DIY reach, but consider calling a qualified carpenter if:
- The door is a fire-rated or acoustic door — modifications may affect its rating and compliance with the NZ Building Code.
- The door frame or lining is also damaged and needs repair.
- You're not confident with power tools or the door is an unusual size or construction.
- The lockset involves any electrical components (e.g. electric strikes or smart locks wired to mains power) — electrical work is restricted work under NZ law and must be carried out by a registered electrician. Check the Electrical Workers Registration Board (EWRB) for what's permitted.
A skilled local carpenter can have this job done quickly and correctly. You can find qualified tradespeople in your area on tradedirectory.co.nz.