Filling Gaps Between Floorboards: Resin vs Slivers
What works, what lasts and what to expect
In older properties, gaps between boards are almost inevitable. Apart from the draughts, gaps collect dirt and can spoil the look of a freshly restored floor. Filling them is a popular part of a floor restoration, but it helps to understand how each method works and what it can and cannot do.
Resin and sanding dust
With this method, a clear resin is mixed with fine dust collected from sanding your own floor, creating a paste that matches the timber. The paste is trowelled into the gaps across the whole floor, left to dry and then sanded flush. It works best on fine gaps, cracks and holes rather than wide openings.
Blends well, since the filler contains your own timber.
Efficient and affordable for larger areas.
Suits narrow gaps rather than wide ones.
May crack when the floor moves with the seasons.
Method two: timber slivers
Wider gaps are better filled with slivers: tapered strips of matching timber glued and fitted into place. After the glue sets, the strips are trimmed and sanded level. Being real timber, slivers accept oil or lacquer like the surrounding boards. The work is slower and more skilled, so it costs more than resin.
Why gaps can come back
It is important to understand that wood is a natural material that moves throughout the year. Boards take in moisture in damp weather and dry out when the heating is on, expanding and contracting as they do. Structural movement in joists and the building adds to this, particularly on suspended timber floors.
That movement means fillers of any kind may crack, shrink or eventually loosen. This is not a sign of poor workmanship; it is simply how wooden floors behave. For this reason, gap filling is excluded from our service guarantee, while the sanding and finishing themselves remain covered. We will always explain this before you decide.
Tips for better results
Try to keep humidity and temperature reasonably stable.
Secure any loose boards first.
Match the method to the gap size.
Consider fitting insulation under suspended floors where possible.
How gap filling fits into a restoration
In most cases, gaps are filled during a floor restoration, not as a separate job. The floor is first sanded with a coarse abrasive to flatten the boards and remove the old finish. The gaps are then cleaned out and filled, and once the filler or slivers have set, the floor is sanded again with finer abrasives. This means the repairs are sanded flush with the boards and take the finish in the same way as the rest of the floor.
Done at the right point in the process, gap filling blends in far better. It also gives us the chance to look at each gap and pick the best approach for its size and position.
Draughts and energy efficiency
Beyond the look of the floor, filling gaps can make a room feel noticeably warmer. Suspended timber floors in older homes often have a ventilated void beneath them, and cold air can rise through every gap. Sealing the gaps cuts draughts, but the space below must still be ventilated through the airbricks to avoid damp problems.
Key points to remember
Resin mixed with your floor's own sanding dust is ideal for narrow gaps, cracks and nail holes.
Reclaimed timber slivers are stronger and more natural-looking in gaps wider than a few millimetres.
Seasonal and structural movement affects every timber floor, so all fillers can eventually crack or work loose.
Because of this natural movement, gap filling is excluded from our service guarantee.
Securing loose boards, keeping humidity steady and ventilating the void below help the filling last.
Which method is right for you?
For floors with mostly narrow gaps, resin is usually the practical, affordable choice. Where gaps are wider than a few millimetres, slivers give a stronger, more natural finish. Many floors benefit from a mix of both. You can read more about our gap filling service, or ask us to assess your boards during a free survey in Surrey.