Installing cornice is one of the more achievable DIY carpentry tasks for a NZ homeowner — it adds a polished finish to any room and, with patience and the right technique, you can get professional-looking results. The key skills are accurate measuring, clean mitre cuts, and neat adhesive application.
What Type of Cornice Should You Use?
In New Zealand, you'll commonly find two types of cornice available at hardware stores:
- Plaster (fibrous) cornice — the traditional choice, heavier, more durable, and gives a high-quality finish. Commonly used in older NZ homes.
- Foam (polystyrene) cornice — lightweight, easy to cut, and more forgiving for beginners. Less durable but a good budget option.
For most standard rooms, a 75 mm or 90 mm cove cornice is a popular choice. Larger ornate profiles suit older villas and bungalows. Check what's available at Bunnings or Mitre 10, and match the profile to your home's style where possible.
Tools and Materials You'll Need
- Cornice lengths (measure up and buy 10–15% extra for waste)
- Cornice adhesive (ask in-store for a product compatible with your cornice type)
- Mitre box or drop saw
- Tape measure and pencil
- String line or chalk line
- Broad-bladed scraper or filling knife
- Fine-grit sandpaper
- Bucket, sponge, and water
- Cornice cement or jointing compound for filling gaps
- Painter's tape
Step 1 — Measure the Room
Measure each wall carefully, noting the length of each run. Sketch a simple plan of the room and mark which corners are internal (inside corners, typically 90°) and which are external (outside corners, such as on a chimney breast or bay). Most rooms have only internal corners, which are slightly easier to cope or mitre.
Add up your total linear metres and add at least 10–15% for cutting waste and mistakes.
Step 2 — Prepare the Surfaces
Clean the wall and ceiling junction thoroughly. Remove any old paint build-up, dust, or grease. If you're working on GIB plasterboard, make sure the stopping is fully cured and sanded smooth before you begin. Lightly dampen plaster surfaces just before applying adhesive — this helps bonding.
Mark a guideline on both the wall and ceiling using a pencil and tape measure, set at the width of your cornice profile. This gives you a consistent line to press the cornice against.
Step 3 — Cutting the Mitres
This is where most beginners struggle. The golden rule: always do a dry fit before applying adhesive.
Internal Corners
Set your mitre box or drop saw to 45°. For an internal corner:
- The piece going left-to-right is cut with the mitre facing one direction.
- The joining piece is cut at the opposing 45° so the two faces meet neatly.
A helpful tip — hold the cornice in the mitre box upside down, with the ceiling edge flat on the base and the wall edge against the fence. This mimics the installed position and makes it easier to visualise the cut direction.
External Corners
External corners are cut in the opposite direction. Again, dry-fit first and adjust if needed — old NZ homes often have corners that aren't perfectly square, so you may need to trim slightly.
Long Straight Runs
For walls longer than one cornice length, join pieces mid-run with a 45° scarf joint (an angled overlap), not a straight butt joint. This hides any shrinkage gap over time.
Step 4 — Applying Adhesive and Fixing
- Mix your cornice adhesive to a peanut-butter consistency (if using powder type) or use it straight from the tube.
- Apply a continuous bead along both edges of the cornice back — the ceiling edge and the wall edge.
- Press the cornice firmly into position along your guidelines, sliding it slightly to spread the adhesive.
- Use temporary nails or screws through the cornice face into the wall framing or ceiling to hold it while the adhesive sets — remove these once cured and fill the holes.
- Wipe away any squeeze-out immediately with a damp sponge.
Step 5 — Filling and Finishing
Once the adhesive has set (check the manufacturer's instructions — typically a few hours), fill all joints, mitre lines, and nail holes with cornice cement or jointing compound. Feather the edges smooth with a damp finger or filling knife. Allow to dry fully, then sand lightly with fine-grit paper.
Prime before painting — bare plaster cornice is porous and needs a good primer coat before your topcoat. Resene and Dulux both offer suitable water-based primers for interior plaster surfaces.
Tips for a Professional Finish
- Work in order around the room — start with the longest wall and work into corners.
- Keep a bucket of clean water handy to keep tools and your hands clean.
- Don't rush the filling stage — neat, well-filled joints make the biggest difference to the final look.
- In humid NZ climates (especially in Auckland or coastal areas), allow extra drying time before sanding and painting.
When to Call a Professional
Cornice installation is generally not restricted work under the NZ Building Code, so homeowners can tackle it themselves. However, consider calling a qualified carpenter or plasterer (find one on tradedirectory.co.nz) if:
- You're working in a heritage home with ornate or custom profiles that need to be matched.
- The existing ceiling or wall substrate is damaged and needs repair first.
- You're uncomfortable working on ladders for extended periods — working at height carries real risk, and WorkSafe NZ recommends taking falls seriously even at low heights.
- The room is very large or has complex geometry.
No electrical, plumbing, or gasfitting work is involved in cornice installation, so there are no licensing requirements to worry about for this task.