For most old pine floors, 40 to 60 grit is the right starting point. If the floor has heavy paint, thick varnish, or significant cupping and unevenness, begin at 40 grit. For floors in better condition with a thinner finish, 60 grit is usually sufficient to get things moving without being overly aggressive. From there, you work up through progressively finer grits until you reach a smooth, ready-to-finish surface.
Why Starting Grit Matters So Much
Pine is a softwood, which means it scratches and dents more easily than hardwoods like rimu or oak. Choosing a grit that's too coarse can leave deep scratch marks that are difficult to remove later, while starting too fine means the machine won't cut through old finish efficiently — you'll burn through sandpaper and time. Getting the starting grit right saves you money on abrasives and protects the timber.
Assessing Your Floor Before You Start
Before hiring a drum sander or belt sander, take a good look at your floor:
- Heavy paint or multiple layers of varnish: Start at 36–40 grit
- Single coat of old varnish or polyurethane, floor reasonably flat: Start at 60 grit
- Lightly worn floor, just refreshing: Start at 80 grit
- Boards with cupping, crowning, or significant height differences: Start at 36–40 grit, and consider running the first pass at a 45-degree angle to the boards to level them
If you're unsure, start with 60 grit on a small, inconspicuous area. You'll quickly see whether it's cutting through the old finish or just polishing it.
A Typical Grit Progression for Old Pine
Here's a general sequence that works well for most old NZ pine floors:
| Pass | Grit | Purpose |
|---|---|---|
| 1st | 36–60 | Remove old finish, level boards |
| 2nd | 60–80 | Remove scratches from first pass |
| 3rd | 80–100 | Smooth the surface |
| Final | 100–120 | Ready for staining or finishing |
Each pass should remove the scratch marks left by the previous grit. Don't skip grits — jumping from 40 straight to 120 will leave visible scratches under your finish coat.
Equipment: Drum Sanders vs. Orbital Sanders
Drum sanders (also called belt sanders) are the workhorses for the main floor area. They're aggressive and fast, which is exactly what you need for the first passes. However, they can gouge pine quickly if you stop moving or tilt the machine — always keep it moving.
Random orbital floor sanders (sometimes called planetary or multi-disc sanders) are gentler and better suited to the final passes. They leave fewer visible scratch patterns, which matters on soft pine.
Edge sanders handle the perimeter where the drum sander can't reach. Use the same grit progression around the edges as you do on the main floor.
You can hire drum sanders and edge sanders from most Bunnings or Mitre 10 stores, or from specialist hire companies.
Tips Specific to Old NZ Pine
- Check for nail heads before you start. Raised nails will tear your sandpaper and can be dangerous. Punch all nails at least 3mm below the surface.
- Old NZ native pine (rimu, matai, heart pine) can be harder than modern radiata pine. If you're unsure what species you have, err on the side of a finer starting grit.
- Lead paint risk: Homes built before 1980 may have lead-based paint on floors. If you suspect lead paint, test before sanding. Sanding lead paint creates hazardous dust — check guidance from WorkSafe NZ before proceeding, and consider hiring a professional.
- Dust extraction: Always use a sander with dust extraction and wear a properly rated dust mask (P2 minimum). Pine dust is a respiratory irritant.
- Grain direction: Always sand with the grain on your finishing passes. The first levelling pass can go at 45 degrees if needed, but subsequent passes must follow the grain.
Finishing After Sanding
Once you've reached your final grit (100–120), vacuum thoroughly, then wipe the floor with a tack cloth or slightly damp cloth to pick up fine dust. Allow to dry completely before applying your chosen finish — whether that's a water-based polyurethane, oil-based varnish, or a penetrating oil. Resene, Dulux, and Wattyl all offer floor finishing products suited to pine, with specific application guides on their websites.
For best results, apply finish in the direction of the grain and follow the manufacturer's recoat times carefully.
When to Call a Professional
Floor sanding is satisfying DIY work, but there are situations where a professional floor sander is the smarter choice:
- Severely cupped, twisted, or damaged boards that need expert assessment before sanding
- Suspected lead paint — a professional with the right equipment and training should handle this
- Heritage or character homes where the floors are irreplaceable and mistakes are costly
- Large areas where hiring and learning to use a drum sander safely may not be cost-effective
- Floors that have been sanded multiple times — pine boards can only be sanded so many times before they become too thin
A qualified floor sanding professional will assess your floor, choose the right approach, and deliver a consistent result. You can find experienced local floor sanders on tradedirectory.co.nz.
