Tongue-and-groove (T&G) panelling shrinking and leaving gaps is one of the most common timber complaints in New Zealand homes — especially in older villas and bungalows, or in rooms with variable humidity. The good news is that minor gaps can often be fixed with straightforward DIY methods, while more serious movement may need a qualified joiner to assess and repair properly.
Why Does Tongue-and-Groove Panelling Shrink?
Timber is a natural, hygroscopic material — it absorbs and releases moisture depending on the surrounding environment. When indoor humidity drops (common in NZ winters with heating running), timber loses moisture and shrinks across the grain, pulling boards apart and opening gaps at the joints.
Common causes include:
- Seasonal humidity swings — particularly in dryer inland regions or well-heated rooms
- Timber installed before it was fully acclimatised — green or wet timber will shrink significantly as it dries
- Poor ventilation — fluctuating moisture levels accelerate movement
- Age — older rimu, matai, or native timber panelling in NZ homes has often dried out considerably over decades
Understanding the cause helps you choose the right fix. If gaps open in winter and close in summer, the timber is still moving seasonally and a rigid filler may crack repeatedly.
Assessing the Gap — How Bad Is It?
Before reaching for the filler, measure and assess:
| Gap Width | Likely Cause | Recommended Fix |
|---|---|---|
| Under 2 mm | Normal seasonal movement | Flexible filler or leave it |
| 2–5 mm | Moderate shrinkage or drying | Flexible caulk or timber filler |
| 5–10 mm | Significant drying or poor installation | Reposition boards or insert a filler strip |
| Over 10 mm | Structural movement or severe shrinkage | Replace boards; consult a joiner |
Also check whether the gap is consistent along the board or wider at one end — uneven gaps can indicate framing movement rather than simple timber shrinkage, which may need further investigation.
DIY Fix Option 1 — Flexible Filler or Caulk
For gaps under about 4–5 mm that are in a painted or primed surface, a flexible acrylic gap filler (paintable caulk) is a practical solution.
- Clean the gap — remove dust, old paint flakes, and any loose material with a vacuum and a stiff brush.
- Apply painter's tape either side of the gap to keep edges neat.
- Apply flexible acrylic filler with a caulking gun, pressing it into the gap.
- Smooth with a damp finger or spatula, then remove the tape before the filler skins over.
- Once cured, sand lightly and repaint to match the surrounding surface.
Avoid rigid fillers like standard interior filler compounds in areas with ongoing movement — they will crack as the timber expands and contracts. Look for products labelled as flexible or gap-filling caulk at Bunnings or Mitre 10.
DIY Fix Option 2 — Timber Filler Strip
For gaps of 5 mm or more on natural or stained timber (where caulk would look wrong), a thin timber filler strip is a more authentic repair.
- Mill or purchase a thin strip of matching timber — ideally the same species (rimu, pine, etc.).
- Plane or sand the strip to fit snugly in the gap without forcing it.
- Apply a small amount of PVA wood glue to both sides of the strip.
- Tap the strip gently into the gap with a rubber mallet.
- Once dry, plane or sand flush, then finish to match (stain, oil, or clear coat).
Matching native NZ timbers like rimu can be tricky — check with a local timber merchant or PlaceMakers for offcuts.
DIY Fix Option 3 — Re-Packing or Repositioning Boards
If multiple boards have all shifted and gaps are consistent across a wall or ceiling, it may be possible to re-pack the boards by removing the end trim, gently tapping boards back together with a block and mallet, and re-fixing. This works best when:
- The boards are not painted in (paint bridging the joints will crack)
- Fixings are accessible (secret-nailed boards are easier than face-nailed)
- The cumulative gap is manageable
This is more involved and risks damaging boards if done carelessly. If you're not confident, this is a good point to call in a joiner.
Preventing Future Shrinkage
- Maintain stable indoor humidity — aim for 45–60% relative humidity year-round. A humidifier in winter can help significantly.
- Acclimatise new timber for at least one to two weeks in the room before installation.
- Seal all surfaces of timber panelling (front, back, and edges) with a quality primer or finish to slow moisture exchange. Resene and Dulux both offer suitable timber primers.
- Ensure the room has adequate ventilation — relevant to Healthy Homes standards for rental properties.
When to Call a Professional
Call a qualified joiner if:
- Gaps are larger than 10 mm or boards are warping or cupping
- You suspect framing movement rather than simple timber shrinkage
- The panelling is in a wet area (bathroom, laundry) — moisture management in these zones is covered under NZ Building Code clause E3 (internal moisture) and related clauses, and poor repairs can cause hidden damage, and poor repairs can cause hidden damage
- You need to replace multiple boards and want a seamless, matched result
- The panelling is heritage or character timber that you don't want to risk damaging
A licensed joiner will also be able to advise whether any work requires a building consent — most cosmetic repairs are exempt under Schedule 1 of the Building Act, but always confirm with your local council if you're unsure. You can find experienced local joiners on tradedirectory.co.nz.
