Rimu and kauri floors can absolutely be sanded and restored, but they require a noticeably different approach to pine. These native NZ timbers are harder, more resinous, and far more sensitive to over-sanding than the softwood pine floors common in many New Zealand homes. Get the technique wrong and you risk irreversible damage to irreplaceable timber.
Why Rimu and Kauri Behave Differently to Pine
Pine is a softwood — relatively forgiving, open-grained, and quick to cut. Rimu and kauri are hardwoods (or close to it in density), with tighter grain structures and natural resins that affect how abrasives cut and how finishes bond.
- Rimu has an interlocked, wavy grain that can tear or feather if you sand too aggressively or go against the grain.
- Kauri is dense and resinous. The resin can clog abrasive belts quickly and can also bleed through some finishes if the timber isn't properly prepared.
- Both timbers are thinner on average in older NZ homes — many rimu and kauri floors have already been sanded once or twice over their lifetime, leaving less material to work with.
Because these floors are often over 80–100 years old and cannot be replaced with new native timber (kauri is now a protected species), treating them with care is essential.
Grit Sequence: Start Coarser on Pine, Gentler on Rimu and Kauri
For a typical pine floor in reasonable condition, many floor sanders start with 40-grit on a drum or belt sander to remove old finish and level the boards, then progress through 60, 80, and finish with 100–120 grit.
For rimu and kauri, a more conservative approach is recommended:
| Stage | Pine (typical) | Rimu / Kauri (recommended) |
|---|---|---|
| Opening cut | 36–40 grit | 60 grit (or 80 if finish is light) |
| Intermediate | 60–80 grit | 80–100 grit |
| Finishing | 100–120 grit | 120 grit |
| Edge sanding | Match drum grit | Match drum grit, use care at edges |
Starting too coarse on rimu or kauri removes too much timber in a single pass and can create visible sanding marks that are difficult to remove without further thinning the boards.
Key Technique Differences
Always Sand With the Grain
This applies to all timber, but it's especially critical with rimu's interlocked grain. Even slight diagonal passes can leave scratches that show up badly under a clear finish.
Watch Your Drum Pressure and Speed
Don't let a drum sander sit stationary on rimu or kauri — even briefly. The machine will cut a visible dip into the surface. Keep moving at a steady, controlled pace.
Manage Resin in Kauri
Kauri's natural resins can gum up belts and sheets faster than pine. Change abrasives more frequently than you think you need to. Clogged abrasives burnish rather than cut, which can close the grain and cause adhesion problems with your finish. Some tradespeople lightly clean the surface with a compatible solvent before finishing — check your finish manufacturer's recommendations first.
Edge Sanding Needs Extra Care
Edge sanders are aggressive. On thin rimu or kauri boards near walls and in corners, use a finer grit than you might on pine and keep the machine moving. Hand scraping or a random orbital sander is sometimes a better option near delicate edges.
Check Board Thickness Before You Start
Use a moisture meter and, if possible, check the board thickness at a vent or access point. If boards are already thin (under about 12–15 mm), consult a professional floor sander before proceeding — there may not be enough material left for a safe sand.
Choosing the Right Finish for Native Timbers
The finish you choose matters as much as the sanding. Rimu and kauri have natural oils and resins that can interfere with some finishes:
- Water-based polyurethane is popular and low-odour, but test adhesion on a small area first, especially with kauri.
- Oil-based polyurethane penetrates well and is a traditional choice for native timbers, though it has longer dry times and stronger fumes — ensure good ventilation.
- Hardwax oils suit rimu well and are easier to spot-repair later.
- Avoid wax-only finishes in high-traffic areas — they wear quickly on harder timbers.
Brands like Resene, Dulux, and Wattyl all offer floor finish ranges — check their technical data sheets for suitability with native NZ timbers before purchasing.
Dust and Safety
Sanding any timber generates fine dust. Rimu and kauri dust can be an irritant — wear a properly rated dust mask (P2 minimum), eye protection, and hearing protection when operating sanders. Ensure the room is well ventilated and seal off doorways to contain dust spread. Check WorkSafe NZ guidance on working safely with wood dust.
When to Call a Professional
Sanding rimu or kauri floors is one of those jobs where experience makes a significant difference. Consider hiring a qualified floor sanding professional if:
- Your boards are already thin or have been sanded before
- There is significant cupping, crowning, or movement between boards
- You're unsure of the timber species or its condition
- The floor has sentimental or heritage value
- You've never operated a drum sander before
A professional floor sander will assess the floor, recommend the right grit sequence, and know when to stop. You can find experienced local floor sanding tradespeople on tradedirectory.co.nz.
Sources & Further Reading
- BRANZ – Timber Floors — research and guidance on NZ building materials including timber
- WorkSafe NZ – Wood Dust Safety — health and safety when sanding
- Resene – Floor Coatings — finish selection and technical data sheets
- Wattyl – Floor Finishes — product guidance for NZ timber floors
- MBIE Building Performance — NZ Building Code context for flooring work
