Nail heads sticking up above your floorboards are one of the most common — and most damaging — problems you'll face when sanding a timber floor. The good news is the fix is straightforward: every nail head needs to be punched below the surface before a sander touches the floor. Skip this step and you'll shred expensive abrasive belts, gouge your boards, and potentially damage a hired drum sander.
Why Protruding Nails Are Such a Problem
Drum sanders and belt sanders spin abrasive paper at high speed. A single nail head sitting even 1–2 mm proud of the surface can tear a sanding belt in seconds, leaving a deep scratch across your board and costing you the price of a replacement belt. On a floor with many protruding nails, you could burn through a whole box of belts before you've covered a few square metres. Beyond the cost, a snagged belt can cause the machine to kick or jolt unexpectedly, which is a real safety hazard.
What You'll Need
- Nail punch (also called a nail set) — use one that matches the nail head diameter
- Hammer (a standard claw hammer works fine)
- Pry bar or flat bar (for any nails that are badly bent or lifting)
- Wood filler or two-part epoxy filler — choose a stainable product if you plan to apply a tinted finish
- Putty knife or filling knife
- Knee pads (you'll be on the floor a while)
- Safety glasses
- Drum sander or belt sander (hire from a local hire company)
- Edge sander
- Sandpaper in assorted grits (typically 40, 60, 80, and 120)
Step 1 — Inspect the Entire Floor
Before you do anything else, get down low and look across the floor at a raking angle — a torch held at floor level works brilliantly for this. Mark every protruding nail with a pencil or chalk so you don't miss any. On older NZ villas and bungalows with rimu or kauri floors, you may find hundreds of nails across a single room, especially if the boards have dried and shrunk over the decades, allowing nail heads to rise.
Step 2 — Punch Every Nail Below the Surface
Using your nail punch and hammer, drive each nail head at least 3 mm below the surface — deeper is fine. Place the tip of the punch squarely on the nail head, hold it firmly, and give it two or three solid strikes. Work methodically across the room so you don't miss any. If a nail is badly corroded, bent, or won't punch down, use a pry bar to remove it entirely and replace it with a new lost-head nail or a decking screw, then punch or countersink that below the surface too.
Safety note: Always wear safety glasses when punching nails — small metal fragments can fly up unexpectedly.
Step 3 — Fill the Nail Holes
Once all nails are punched, fill the holes with a timber filler or wood putty. For floors that will be clear-coated, choose a filler that closely matches your timber species. For painted floors, any good-quality interior filler will do. Press the filler firmly into each hole with a putty knife, slightly overfilling so it can be sanded flush. Allow it to dry fully according to the manufacturer's instructions before sanding — rushing this step leads to soft spots that sand unevenly.
Step 4 — Do a Final Check Before Sanding
Once the filler is dry, run your hand flat across the floor in all directions. You should feel no snags or high spots. Do one more pass with your torch at a raking angle. If you find any nail heads you missed, punch them now — it's much easier to do this before the sander is running.
Step 5 — Sand the Floor
With all nails punched and holes filled, you're ready to sand. Start with a coarser grit (typically 40 grit) on the drum or belt sander to level the surface and remove old finish, then work progressively through finer grits (60, 80, 120). Always sand with the grain of the timber. Use an edge sander for the perimeter, and a detail sander or hand-sanding block for corners the machines can't reach.
| Grit | Purpose |
|---|---|
| 40 | Heavy material removal, levelling old boards |
| 60 | Removing 40-grit scratches, further levelling |
| 80 | Smoothing, preparing for finish coats |
| 120 | Final pass before applying finish |
For guidance on finishing products suited to NZ conditions, Resene and Wattyl both offer floor coatings with technical data sheets available on their websites.
Hiring Equipment in NZ
Drum sanders and edge sanders are widely available from hire centres across New Zealand. Bunnings and Mitre 10 hire equipment at many locations, as do specialist hire companies. When you pick up the machine, ask staff to demonstrate how to fit and tension the sanding belt — an incorrectly fitted belt is a common cause of damage to both the machine and your floor.
Dust and Health Considerations
Timber dust is a respiratory hazard. Older NZ homes may also have lead-based paint on floors painted before the 1970s. If you suspect lead paint, get the surface tested before sanding. WorkSafe NZ has guidance on working safely with hazardous substances. Always wear a properly fitted P2 dust mask (not just a paper dust mask), and ensure the room is well ventilated. Seal doorways with plastic sheeting to contain dust.
When to Call a Professional
Floor sanding is physically demanding and the machines are powerful — mistakes can mean gouging or unevenly sanding boards that are difficult or impossible to reverse. If your floor has very thin boards (already sanded multiple times), significant structural damage, or boards that are loose and springy underfoot, it's worth getting a professional floor sander to assess the job first. A qualified tradesperson will also have commercial-grade equipment and the experience to handle tricky situations like parquet, herringbone patterns, or severely cupped boards. You can find experienced local floor sanders on tradedirectory.co.nz.
Note that structural repairs to subfloors may require a building consent depending on the scope of work — always check with your local council. The MBIE Building Performance website has useful information on what work requires consent.
