For most painted timber joinery — window frames, door frames, skirting boards, and architraves — a two-part epoxy wood filler or a quality acrylic-based wood filler will give the most durable, long-lasting result. The right choice depends on the size and depth of the repair, whether the timber is interior or exterior, and the final finish you're after.
Understanding the Main Types of Wood Filler
Not all wood fillers are created equal. Here's a breakdown of the most common types available in New Zealand and where each one performs best:
| Filler Type | Best For | Paintable? | Stainable? | Interior/Exterior |
|---|---|---|---|---|
| Acrylic wood filler | Small holes, cracks, nail holes | Yes | Limited | Both (check label) |
| Solvent-based filler | Medium repairs, harder finish | Yes | Limited | Both |
| Two-part epoxy filler | Large repairs, rot damage, structural | Yes | No | Both |
| Timber putty | Nail holes before painting | Yes | Some types | Interior mainly |
| Flexible sealant/filler | Moving joints, gaps around frames | Yes | No | Both |
Acrylic Wood Fillers: The Everyday Choice
Acrylic fillers are water-based, easy to sand, and widely available at Bunnings and Mitre 10. They're ideal for filling small nail holes, minor cracks, and surface imperfections in interior joinery before painting. They dry relatively quickly and clean up with water.
The downside is that acrylic fillers can shrink slightly as they cure, so for deeper repairs you'll need to apply them in layers. They're also not the best choice for exterior joinery that's exposed to the full NZ weather cycle — repeated wetting and drying can cause them to crack or lift over time.
Two-Part Epoxy Fillers: The Professional's Pick
For exterior timber joinery, larger voids, or any area where rot has been cut back, a two-part epoxy wood filler is the gold standard. These products consist of a base and a hardener that you mix together. Once cured, epoxy filler is extremely hard, dimensionally stable, and won't shrink or crack. It can be shaped, drilled, planed, and painted just like timber.
Epoxy fillers are particularly well-suited to New Zealand's variable climate — from the humidity of Northland to the freeze-thaw cycles in Central Otago. Brands like Sika offer epoxy-based repair products suitable for timber. Always follow the manufacturer's mixing ratios carefully, as incorrect mixing will result in a soft or tacky cure.
Important: Two-part epoxy fillers are generally not suitable for staining, as they won't absorb timber stain. If you're repairing stained or clear-finished joinery, matching the colour is tricky — consult a joiner.
Timber Putty: For Nail Holes and Fine Finishing
Timber putty (sometimes called wood putty or stopping) is a softer, oil-based product traditionally used to fill nail holes in joinery before painting. It stays slightly flexible, which can be an advantage in moving timber. However, it's generally not suitable for large repairs and can take a long time to fully harden before painting.
For a painted finish, many professional joiners and painters use a stiff acrylic filler or a purpose-made stopping compound for nail holes, as these sand back more cleanly.
Flexible Fillers for Gaps Around Frames
If you're dealing with a gap between a door or window frame and the surrounding wall — rather than damage to the timber itself — a paintable flexible sealant is the right product, not a rigid wood filler. Rigid fillers will crack as the building moves. Look for a paintable acrylic or polyurethane sealant rated for exterior use if the gap is exposed to weather.
Preparing the Timber Before Filling
Good preparation is everything. Follow these steps for a lasting repair:
- Remove all rot or loose timber before filling — epoxy filler over soft rot will fail.
- Clean the area of dust, grease, and old paint flakes.
- Prime bare timber before applying acrylic filler, or use an epoxy consolidant (a liquid primer designed for use with epoxy fillers) on any timber that has been affected by rot.
- Apply filler slightly proud of the surface, then sand back flush once cured.
- Prime and paint the repair promptly — bare filler left exposed to UV will degrade.
For exterior joinery, always finish with a quality exterior paint system. Resene and Dulux both offer exterior timber paint systems with good UV and moisture resistance suited to NZ conditions.
Matching Stained or Clear-Finished Timber
If your joinery has a stained or clear finish, matching a repair is significantly harder. Most fillers won't take stain the same way timber does. Some specialist timber putties come in a range of timber tones, but a perfect match is rarely achievable with filler alone. For visible, high-quality joinery, it's worth consulting a professional joiner.
When to Call a Professional
Some joinery repairs go beyond what a filler can fix. Call a qualified joiner if:
- Rot is extensive and has spread into the structural section of a window or door frame.
- The joinery is failing — gaps, draughts, or water ingress suggest the frame may need replacing rather than patching.
- The repair is on a heritage or high-value home where appearance is critical.
- You're unsure whether the damage is cosmetic or structural — a professional assessment is always worthwhile.
You can find qualified local joiners and tradespeople on tradedirectory.co.nz. For work that affects weathertightness, be aware that significant alterations to exterior joinery may require a building consent — always check with your local council. The MBIE Building Performance website has guidance on when consent is required.
