Sanding old rimu floors correctly comes down to using the right sequence of grits — moving from coarse to fine in stages to remove old finish, level the boards, and prepare a smooth surface for your new coating. Rush the process or skip a grit, and you risk deep scratches, uneven staining, or a finish that won't last. Here's how to do it properly.
Why Grit Sequence Matters for Rimu
Rimu (Dacrydium cupressinum) is a native NZ timber with a relatively open, interlocked grain. Compared with harder imported timbers, rimu is more prone to sanding scratches showing through the final finish, especially under stains or oils. This makes a disciplined grit progression essential — each pass removes the scratch marks left by the previous, coarser grit.
Old rimu floors also commonly have multiple layers of polyurethane, wax, or even old shellac-based finishes that need to be fully stripped before you can achieve a consistent result.
The Standard Grit Sequence
The sequence below is for a drum sander (main field) combined with an edge sander and a detail sander for corners. Always work at a slight diagonal (around 5–15°) on the first pass, then parallel to the boards on subsequent passes.
| Pass | Grit | Purpose |
|---|---|---|
| 1st | 36–40 grit | Strip old finish, level cupped or uneven boards |
| 2nd | 60 grit | Remove coarse scratches, begin smoothing |
| 3rd | 80 grit | Refine surface, remove 60-grit marks |
| 4th | 100 grit | Final smoothing before coating |
When to Start Coarser
If your rimu floor has heavy paint, thick wax build-up, or significant cupping, you may need to begin with 24 grit before stepping up to 36–40. Be cautious — coarser grits remove timber quickly and rimu boards can be thin after decades of previous sanding. Check board thickness before you start; if boards are already quite thin (under about 12 mm above the tongue), consult a professional floor sander before proceeding.
When You Can Start Finer
If the floor is in good condition with only a light coat of finish and minimal unevenness, you may be able to start at 60 grit and finish at 100 grit, saving time and timber. Assess carefully before committing.
Step-by-Step Process
- Prepare the room — remove all furniture, nail down any raised nails or staples (a nail punch and hammer are essential), and seal doorways with plastic sheeting to contain dust.
- First pass (36–40 grit) — run the drum sander at a slight diagonal across the grain to cut through old finish evenly. Keep the machine moving at all times to avoid gouging.
- Edge sand — use the edge sander with the same grit along skirting boards and edges the drum can't reach.
- Second pass (60 grit) — now run parallel to the boards. Overlap each pass by about one-third of the drum width.
- Third pass (80 grit) — same direction, parallel to boards. The floor should start looking noticeably smoother.
- Final pass (100 grit) — this is your finishing pass. Take your time and ensure even coverage across the whole floor.
- Detail sand corners — use a detail or oscillating sander to reach right into corners and tight spots the edge sander missed.
- Vacuum and tack — vacuum thoroughly, then wipe down with a tack cloth to remove all fine dust before applying any finish.
Choosing the Right Finish for Rimu
Once sanded to 100 grit, rimu takes a range of finishes well. Water-based polyurethane is popular for its low odour and fast dry time. Oil-based polyurethane gives a warmer amber tone that suits rimu's natural reddish hue. Hardwax oils are another option for a more natural look. Always check the finish manufacturer's recommendations — some products require a light 120-grit screen sand between coats.
For colour guidance and compatible timber coatings, Resene and Wattyl both offer NZ-stocked timber floor finishes with technical data sheets worth reading before you buy.
Dust and Safety
Floor sanding generates significant fine dust — a serious health hazard with prolonged exposure. Always wear a P2-rated dust mask (not just a paper dust mask), safety glasses, and hearing protection. Ensure good ventilation. Rimu dust, like all timber dusts, can be an irritant. Review safe work practices at WorkSafe NZ before starting.
Old floors in homes built before the 1980s may also have lead-based paint as an undercoat. If you suspect lead paint, get the surface tested before sanding — disturbing lead paint creates a serious hazard requiring specialist handling.
When to Call a Professional
Floor sanding is a skill that takes practice. Hiring a qualified floor sander is strongly recommended if:
- Your rimu boards are thin or fragile and at risk of being sanded through
- The floor has significant cupping, crowning, or structural movement
- You suspect lead paint or other hazardous coatings
- You've never operated a drum sander before — these machines can gouge deeply in seconds if not kept moving
- The floor is in a rental property subject to Healthy Homes Standards where a professional finish is important for compliance and tenancy obligations
A professional floor sander will also have commercial-grade dust extraction, reducing mess and health risk significantly. You can find qualified local floor sanders on tradedirectory.co.nz.
