Gaps between floorboards are a very common issue in older New Zealand homes, particularly those built before the 1970s with native timber floors like rimu, kauri, or matai. The good news is that many gaps can be filled as a DIY project — but choosing the right product and method makes all the difference between a fix that lasts and one that cracks out within a season.
Why Gaps Form in Older Timber Floors
Timber is a natural material that expands and contracts with changes in temperature and humidity. In New Zealand's variable climate — from the humid north to the cold, dry winters of the South Island — this movement is significant. Over decades, boards can shrink, warp, or shift, leaving gaps that let in draughts, dust, and even moisture from the subfloor. Addressing gaps also supports the Healthy Homes Standards, which require rental properties to be draught-stopped; see Tenancy Services for details.
Assessing the Gaps Before You Start
Before reaching for a filler, take stock of what you're dealing with:
- Narrow gaps (under 3 mm): Can be filled with a flexible floor sealant or gap filler.
- Medium gaps (3–8 mm): Rope, cork strip, or a thicker flexible filler works well.
- Large gaps (over 8 mm): May need timber infill strips, or the floor may need professional re-laying.
- Uneven or springy boards: Could indicate a structural issue — check the subfloor framing before filling.
Also consider whether the gaps are consistent or variable. If boards are still moving noticeably with the seasons, a rigid filler will crack. Always choose a flexible product for timber floors.
Choosing the Right Filler
| Gap Size | Recommended Product | Notes |
|---|---|---|
| Up to 3 mm | Flexible acrylic gap filler | Paintable, easy to apply |
| 3–8 mm | Cork rope or flexible sealant | Cork compresses with board movement |
| 8–15 mm | Timber filler strips (glued in) | Best colour-matched to existing boards |
| Over 15 mm | Consult a flooring professional | Re-laying may be required |
Cork rope (also called caulking rope or draught-stop rope) is a popular choice for medium gaps in older NZ homes. It's pushed into the gap with a putty knife, stays flexible, and can be stained or painted over. You'll find it at Bunnings or Mitre 10.
For a near-invisible finish on polished floors, timber-coloured flexible fillers or a DIY mix of fine sawdust from the same timber species blended with PVA glue can work well — though the sawdust mix is rigid, so it's best reserved for stable, narrow gaps.
Step-by-Step: Filling Floorboard Gaps
1. Clean the Gaps Thoroughly
Vacuum out dust, grit, and old filler. Use a stiff brush or a flat-blade screwdriver to clear debris. Any contamination will stop the filler bonding properly.
2. Check Moisture Levels
If the subfloor area is damp, address the source before filling. Poor subfloor ventilation is common in older NZ homes and can cause ongoing timber movement and rot. BRANZ has useful guidance on subfloor moisture management.
3. Apply Your Chosen Filler
- For cork rope, press it firmly into the gap using a putty knife, leaving it slightly proud, then trim flush once set.
- For flexible acrylic filler, apply with a caulking gun, smooth with a damp finger or tool, and allow to cure fully before foot traffic.
- For timber strips, cut to width, apply wood glue, tap in gently, and sand flush when dry.
4. Sand and Finish
Once cured, lightly sand the filled areas flush with the surrounding boards. If the floor is to be coated, apply your chosen finish — whether oil, polyurethane, or wax — over the entire floor for a consistent look. Resene and Wattyl both offer floor-specific coating products suited to NZ conditions.
5. Improve Subfloor Ventilation
If gaps are caused partly by moisture-driven movement, consider improving underfloor ventilation. This is a separate project but will reduce future gap formation significantly.
What to Avoid
- Rigid fillers like plaster or standard wall filler — these will crack as the boards move.
- Overfilling — proud filler creates a trip hazard and looks untidy.
- Ignoring the cause — if boards are lifting or the subfloor is damaged, filling gaps is only a temporary fix.
When to Call a Professional
Some floor situations go beyond a DIY gap-fill:
- Structural concerns — bouncy, soft, or badly uneven floors may indicate damaged joists or bearers. This could involve work covered by the NZ Building Code and may require a building consent depending on scope; always check with your local council and visit MBIE Building Performance for guidance on consent requirements.
- Very large or widespread gaps — a flooring specialist may need to re-lay or re-nail the boards.
- Heritage or high-value timber floors — kauri and rimu floors in particular deserve expert attention to preserve their value.
- Subfloor drainage or plumbing issues — any work on drains or pipes must be carried out by a licensed drainlayer or plumber registered with the Plumbers Gasfitters & Drainlayers Board.
A skilled local handyman or flooring specialist can assess your floor and recommend the best approach. You can find qualified tradespeople in your area on tradedirectory.co.nz.
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