How to Fill Gaps in Wooden Floors
Choosing the right method for your floorboards
Most period floors develop gaps over the years as boards dry, shrink and shift. 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
Resin filling uses a clear binder mixed with the fine dust from your own floor, so the colour matches closely. The paste is trowelled into the gaps across the whole floor, left to dry and then sanded flush. It is ideal for narrow gaps, small cracks, splits and nail holes.
Good colour match because it uses your floor's own dust.
Efficient and affordable for larger areas.
Best for gaps of a few millimetres.
Can crack or fall out as boards expand and contract.
Filling with slivers
For wider gaps, thin strips of timber, usually reclaimed pine, are cut to shape, glued on one side and tapped into each gap. Once dry, they are planed and sanded flush with the boards. 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.
Seasonal and structural movement
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. On top of that, the building itself moves slightly, and joists flex as people walk across the floor.
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 make sure you know this before any filling is booked.
Tips for better results
Keep indoor humidity steady and avoid extreme heating swings.
Secure any loose boards first.
Match the method to the gap size.
Insulation beneath the floor can reduce draughts and movement.
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. After that, gaps are cleaned and filled, and the floor is sanded again once everything has set. Sanding after filling leaves the repairs level and ready to take the same finish as the surrounding timber.
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.
Reducing draughts
Filling gaps is not just cosmetic; it can also make a room more comfortable. Suspended timber floors in older homes often have a ventilated void beneath them, and cold air can rise through every gap. Closing those gaps reduces draughts and helps keep heat in the room, although it is important that the void beneath the floor remains properly ventilated to prevent damp.
In summary
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.
That natural movement is the reason gap filling is not covered by our service guarantee.
Stable heating, secure boards and good ventilation under the floor all help filler last longer.
Our recommendation
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. Plenty of floors are best treated with a combination. Find out more about our gap filling service, or ask us to assess your boards during a free survey in Cobham.