A smooth, flawless paint job starts long before you crack open a tin of paint. Filling nail holes and cracks properly is one of the most important — and most overlooked — steps in any interior or exterior painting project. Get it right and your walls will look professionally finished; skip it and every imperfection will show up under fresh paint.
Understanding the Types of Holes and Cracks
Not all holes and cracks are the same, and choosing the right filler depends on what you're dealing with:
- Nail holes and small dents – Tiny punctures left by picture hooks, nails, or screws. Usually less than 5 mm wide.
- Hairline cracks – Fine surface cracks common in plaster and plasterboard walls, often caused by seasonal movement or settling.
- Structural or recurring cracks – Wider cracks (generally over 3 mm), cracks that keep coming back, or cracks with uneven edges on either side. These can signal a more serious issue.
- Exterior cracks – Found in weatherboards, fibre cement cladding, or around window and door frames, exposed to NZ's variable weather.
If you notice large, recurring, or stepped cracks — especially around door frames or foundations — it's worth getting a building professional to assess them before you paint over the problem.
Choosing the Right Filler
Using the correct product makes a big difference to how well the repair holds and how it looks once painted.
| Situation | Recommended Product Type |
|---|---|
| Small nail holes, interior walls | Lightweight interior filler / spackle |
| Larger holes or gouges (up to ~20 mm) | Standard interior wall filler |
| Flexible cracks (around trims, skirtings) | Paintable acrylic sealant / gap filler |
| Exterior cracks and gaps | Exterior-grade flexible filler or sealant |
| Plasterboard repairs | GIB jointing compound or setting compound |
Well-known products available at NZ hardware stores include Spakfilla (a popular lightweight filler), Selleys No More Gaps (for flexible joints), and various Sika gap fillers. For plasterboard work, GIB-brand jointing compounds are the go-to choice. You'll find a good range at Bunnings or Mitre 10.
Tip: Always check the label to confirm the product is suitable for your surface (plaster, plasterboard, timber, or fibre cement) and whether it can be painted over.
Tools You'll Need
- Flexible filling knife or putty knife (75–100 mm is handy for most jobs)
- Fine-grit sandpaper (120–180 grit) and a sanding block
- Damp cloth or sponge
- Primer or primer-sealer
- Safety glasses and dust mask for sanding
Step-by-Step: Filling Nail Holes and Small Cracks
1. Clean and prepare the surface
Remove any loose paint, dust, or debris from around the hole or crack. A damp cloth works well. Allow the surface to dry completely — filler won't bond well to a wet or dusty surface.
2. Apply the filler
Using your filling knife, press the filler firmly into the hole or crack, slightly overfilling it. For deeper holes, apply in thin layers and allow each layer to dry before adding the next — this prevents shrinkage cracking. For flexible joints (like where skirting meets the wall), run a bead of paintable acrylic sealant and smooth it with a damp finger.
3. Allow to dry fully
Drying times vary by product and thickness — check the manufacturer's instructions. Don't rush this step; painting over wet filler causes problems.
4. Sand smooth
Once dry, sand the filled area flush with the surrounding surface using fine-grit sandpaper. Work in a circular motion, then finish with light strokes in one direction. Wipe away dust with a damp cloth and let it dry.
5. Prime the repair
This is a step many DIYers skip — don't. Filler is porous and will absorb paint differently to the surrounding wall, leaving a dull patch (called flashing) once painted. Apply a coat of primer or primer-sealer over the repair and let it dry before painting. Resene and Dulux both offer suitable interior primers widely available in NZ.
6. Paint
Once primed, apply your topcoat. You may need two coats over repaired areas to achieve an even sheen, especially with mid- to high-sheen paints.
Exterior Repairs: Extra Considerations
NZ's climate — UV exposure, humidity, and temperature swings — means exterior repairs need products rated for outdoor use. Use an exterior-grade flexible filler or sealant around window and door frames where movement occurs. For fibre cement cladding like James Hardie products, follow the manufacturer's recommendations for compatible fillers and primers, as some standard fillers don't adhere well to fibre cement.
Always prime exterior repairs before painting to seal the filler and improve paint adhesion.
Common Mistakes to Avoid
- Skipping primer – Almost guarantees visible patching under the topcoat.
- Overfilling in one go – Deep holes filled in a single pass will shrink and crack as they dry.
- Painting too soon – Wet filler under paint leads to bubbling and poor adhesion.
- Using interior filler outside – It will absorb moisture and fail quickly.
- Ignoring the cause – Filling a crack that keeps returning without addressing the underlying movement is a temporary fix at best.
When to Call a Professional
Some situations are beyond a straightforward DIY fill-and-paint job:
- Recurring or widening cracks may indicate structural movement — consult a Licensed Building Practitioner or structural engineer before painting.
- Large plasterboard repairs (replacing sections of GIB board) require skill to achieve a seamless finish and may involve stopping and sanding that's best left to a professional plasterer or painter.
- Extensive exterior cracking around cladding or flashings could point to weathertightness issues — get a professional assessment.
For a high-quality finish on a full repaint, it's always worth getting a professional painter involved. You can find qualified local painters on tradedirectory.co.nz.