Are gaps in floorboards normal?

Yes. Timber shrinks and swells with humidity, so boards open small even gaps in dry months and close them in humid months. Uniform gaps of 1-3mm that change with the seasons are normal behaviour, not a defect.

Should floorboard gaps be filled?

Persistent gaps can be filled during a sand and polish -- with filler mixed from the floor's own sanding dust, or flexible gap fillers, or timber slivers for large gaps. Filling seasonal gaps at their widest (late in a dry winter) backfires: the boards expand in summer and either crush the filler out or, worse, peak against each other.

Why are my floorboard gaps suddenly bigger?

Look for a moisture change: a new heating system or reverse-cycle running all winter, a dried-out subfloor, or long dry weather. If gaps grow alongside cupping, squeaks or a lifting board line, involve a professional -- that pattern points at a moisture or structural movement problem, not cosmetics.

Gaps in Floorboards: Normal, Fixable, or a Problem?

Every board floor has gaps. The question is which kind.

TL;DR Even 1-3mm gaps that breathe with the seasons: normal, leave them or draught-proof from below. Persistent gaps: fillable during a sand -- dust-and-resin for small, timber slivers for large. Fill in the humid season or mid-range, never at peak winter dryness. Uneven, growing, or one-sided gapping with cupped boards: that is a moisture signal, not a cosmetic one -- investigate before filling anything.

Why boards gap

Timber is hygroscopic -- it takes on and gives up moisture with the air, swelling and shrinking across the width of each board. A 100mm-wide hardwood board can move a millimetre or more between a humid summer and a heated winter. Multiply by every board in the room and the floor has to breathe somewhere: the gaps. Old floors laid tight in a different climate era, or floors over newly effective heating, show it most.

The three kinds of gap

What you see	What it is	What to do
Small, even gaps that shrink in summer	Normal seasonal movement	Nothing, or draught-sealing. Managing indoor humidity (40-60%) minimises it -- see the care guide.
Consistent gaps that never close	Permanent shrinkage -- boards dried below their laid size over the years	Fill during the next sand and polish if they bother you. Purely cosmetic.
Uneven, growing, or localised gapping, especially with cupping or peaking	A moisture or structural problem underneath	Investigate first: subfloor ventilation, leaks, drainage. Cupping guide here.

Filling, done properly

Dust-and-resin filler -- the standard method during a sand: the floor's own sanding dust mixed with filler resin, squeezed into the gaps, sanded flush. Perfect colour match by definition. Rigid, so best on gaps up to ~3mm that don't move much.
Flexible gap fillers -- coloured acrylic/polymer fillers that tolerate some seasonal movement. For gaps that breathe.
Timber slivers -- for gaps 5mm+, tapered strips of matching timber glued in and sanded flush. The proper fix for big gaps in old baltic floors; labour-intensive and worth it.

Timing matters more than product. Fill when the boards are mid-range or at their most swollen (humid season) -- never at peak winter dryness. Filler installed into fully open gaps gets crushed when the boards come back, and either squeezes out in ridges or stops the boards closing and drives them into peaking.

Draughts and dirt: the other reasons people fill

On old houses with open subfloors, winter draughts through the gaps are real. Options that work without fighting the timber: draught-proofing strips pushed into the gaps from above (removable, invisible once in), sealing the subfloor perimeter, or underfloor insulation between joists. These solve the comfort problem and let the boards keep moving as designed -- often the better play than filling a whole draughty floor rigid.

Gaps bothering you?

Ring with a photo and the board width. We'll tell you whether yours are seasonal or permanent, whether filling makes sense, and what to fill them with -- or what to check under the floor first.

Call 1300 950 551