Screw and nail holes are an unavoidable part of working with timber, but left unfilled they look untidy and can let moisture in — especially in our damp New Zealand climate. The good news is that with the right filler and a bit of patience, you can make those holes virtually disappear before painting or staining. Here's how to do it properly.
Choosing the Right Filler
Not all fillers are created equal, and picking the wrong one is the most common DIY mistake. The best product depends on whether the timber will be painted or stained, and whether it's interior or exterior.
| Situation | Recommended Filler Type |
|---|---|
| Interior timber, painted finish | Acrylic wood filler / painter's putty |
| Interior timber, stained/clear finish | Tinted timber putty or wax filler stick |
| Exterior timber, painted finish | Flexible exterior wood filler |
| Structural or large holes | Two-part epoxy wood filler |
| Quick touch-up, pre-finished timber | Wax filler crayon/stick |
Acrylic fillers (like those available from Resene or at Mitre 10) are water-based, easy to sand, and paintable — ideal for interior skirting boards, architraves, and shelving. Exterior fillers need to be flexible enough to cope with New Zealand's temperature swings and UV exposure, so always check the label says suitable for outdoor use.
For a stained or clear-coated finish, colour-matching is critical. Wax filler sticks and tinted putties come in a range of timber tones — take a sample piece or photo to your local paint store for help matching.
Tools and Materials You'll Need
- Putty knife or flexible filling knife (75–100 mm wide)
- Fine-grit sandpaper (120–180 grit) and sanding block
- Damp cloth or sponge
- Appropriate filler for your situation (see table above)
- Primer and topcoat paint, or timber stain/oil
- Safety glasses and dust mask for sanding
Step-by-Step: Filling Nail and Screw Holes
1. Prepare the Surface
Make sure the timber is clean, dry, and free of dust, grease, or old flaking paint. If the hole has a raised edge from the nail punch or screw driver, lightly sand it flush first. For exterior timber, check there's no rot around the hole — if there is, the damaged timber needs to be cut out and replaced before filling.
2. Apply the Filler
Using your putty knife, press the filler firmly into the hole, slightly overfilling it — most fillers shrink a little as they dry. For deeper holes (from countersunk screws), apply in two thin layers rather than one thick one, allowing each layer to dry fully. Smooth the surface as best you can with the knife to reduce sanding later.
3. Allow to Dry Fully
Drying times vary by product and conditions. In cooler or humid NZ conditions (common in winter or in southern regions), allow extra drying time. Don't rush this step — painting over wet filler causes cracking and poor adhesion.
4. Sand Smooth
Once fully dry, sand the filled area flush with the surrounding timber using 120–180 grit sandpaper on a sanding block. Always sand with the grain to avoid scratching. Wipe away dust with a damp cloth and let it dry.
5. Prime and Finish
For painted finishes, spot-prime the filled area before applying your topcoat — filler can be more porous than the surrounding timber and will show as a dull patch if you skip this step. Dulux and Wattyl both offer suitable timber primers. For stained finishes, test your stain on a hidden area first, as filler rarely absorbs stain the same way raw timber does.
Tips for a Professional Result
- Punch nails below the surface before filling — a nail punch and hammer set nails 1–2 mm below the face, giving the filler something to grip.
- Don't skip the primer on filled spots before painting — it makes a real difference to the final look.
- For large or structural holes, a two-part epoxy filler (available at Bunnings or PlaceMakers) gives a rock-hard, durable repair that can be drilled and shaped once cured.
- In wet areas like bathrooms or kitchens, use a waterproof filler and ensure the area is properly sealed — refer to the MBIE Building Performance guidance on wet area requirements if you're doing any broader renovation work.
Common Mistakes to Avoid
- Using interior filler outdoors — it will crack and fall out within months
- Underfilling and expecting paint to hide the dip
- Painting before the filler is completely dry
- Using the wrong colour filler under a clear finish
When to Call a Professional
For straightforward nail and screw holes, this is a satisfying DIY job. However, if you're dealing with extensive damage, rot, or structural timber repairs, it's worth getting a qualified carpenter involved. Likewise, if the holes are part of a larger renovation — say, removing walls, replacing weatherboards, or working near electrical cables — a licensed tradesperson is the safe choice. You can find experienced local carpenters on tradedirectory.co.nz to get the job done right.
Always wear a dust mask and safety glasses when sanding, and ensure good ventilation — fine timber dust is a health hazard with repeated exposure. For more on safe DIY practices, WorkSafe NZ has helpful guidance.