Yes, mixing sawdust with wood glue is a well-established DIY method for filling small gaps between floorboards — and it can produce a surprisingly natural-looking result when done correctly. However, it works best for minor gaps and has real limitations, especially in older NZ homes where timber movement is common. Read on to understand when this method suits your situation and how to get the best finish.
How the Sawdust and Wood Glue Method Works
The idea is simple: fine sawdust acts as a filler aggregate, and PVA wood glue (sometimes called carpenter's glue) acts as the binder. When mixed to a thick paste and pressed into gaps, it dries hard and can be sanded flush with the surrounding floor. Because the sawdust ideally comes from the same timber species as your floor, the colour match is often better than off-the-shelf fillers.
What You'll Need
Step-by-Step Guide
- Sand the floor first (or at least the area). Collect the fine dust produced — this is your filler material. Dust from a drum or belt sander is ideal as it's very fine.
- Clean the gaps thoroughly. Vacuum out all loose debris, old filler, and grit. Any contamination will weaken adhesion.
- Mix your filler. Combine sawdust and PVA glue in a small container, stirring until you reach a thick, peanut-butter-like consistency. Don't make it too wet or it will shrink excessively as it dries.
- Press the mix firmly into the gaps using a putty knife, slightly overfilling each gap to allow for shrinkage.
- Allow to dry fully — typically 4–8 hours depending on humidity and gap depth. NZ's variable climate means drying times can be longer in cooler, damper conditions (think South Island winters or older uninsulated subfloors).
- Sand flush once fully cured. Work with the grain to avoid scratching the surrounding boards.
- Apply your finish (oil, polyurethane, or wax) over the entire floor so the filled areas blend seamlessly.
When This Method Works Well
- Gaps up to about 3–4 mm wide and relatively shallow
- Stable, dry timber that isn't subject to significant seasonal movement
- Floors being fully sanded and refinished — the filler integrates best under a fresh coat of finish
- Matching species — using dust from the actual floor gives the closest colour match
Limitations and When It Won't Work
This is where many DIYers run into trouble. Sawdust-and-glue filler is rigid once dry, meaning it can crack or pop out if your floorboards expand and contract with seasonal humidity changes — something very common in NZ homes, particularly those with native timbers like rimu, kauri, or matai.
| Situation | Sawdust & Glue Suitable? |
|---|---|
| Gaps under 4 mm, stable floor | Yes |
| Gaps over 5 mm wide | No — use flexible filler or timber strips |
| Active seasonal movement | No — filler will crack |
| Structural gaps or lifted boards | No — fix the cause first |
| Decorative fill before full sand | Yes, with care |
For wider or structurally significant gaps, consider flexible floor fillers (available from flooring specialists), timber splines glued in place, or consult a professional floor sander. BRANZ has useful guidance on timber floor maintenance and movement that's worth reading before you start.
Colour Matching Tips
Even with matching sawdust, the dried filler often appears slightly darker or lighter than the surrounding boards once a finish is applied. Test a small, hidden area first. If the colour is off, some floor sanders blend in a small amount of Resene or Dulux tint, though this takes practice. Accepting a slight variation is often more realistic than chasing a perfect match.
Preparing Your Subfloor and Checking for Bigger Issues
Before filling gaps, check whether the boards themselves are the problem. Loose, squeaky, or cupped boards should be fixed first — screwing boards down or addressing subfloor moisture issues. If your home has a suspended timber floor (very common in NZ), poor underfloor ventilation can cause ongoing moisture-driven movement. Energywise has information on subfloor insulation and ventilation that may be relevant.
Also be aware that if your home was built before the 1980s, old floor finishes may contain lead paint or other hazardous materials, and older floor coverings or adhesives may contain asbestos. Check with WorkSafe NZ for guidance on safe handling before sanding. Note that asbestos-containing materials may also be present in older homes — check with WorkSafe NZ for asbestos guidance as well.
When to Call a Professional
While filling small gaps is well within DIY reach, there are situations where a qualified floor sanding professional is the smarter call:
- Gaps are widespread, large, or caused by structural movement
- The floor has significant cupping, crowning, or damage
- You're unsure of the timber species or the floor's history
- The floor is a heritage or high-value timber (kauri, native rimu) where mistakes are costly
- You need a consistent, high-quality finish across a large area
A professional floor sander has access to commercial-grade equipment and fillers, and can assess whether your floor needs more than just gap filling. You can find qualified local floor sanders on tradedirectory.co.nz.
Note: Floor sanding and filling is not restricted work under NZ law, so homeowners can legally do this themselves. However, if any electrical work (such as moving skirting-board power outlets) is involved during a floor renovation, that must be carried out by a registered electrician — see the Electrical Workers Registration Board for details.
