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 makes a real difference, but it is important to know what to expect.
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.
Quick and cost-effective across a whole room.
Suits narrow gaps rather than wide ones.
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. After the glue sets, the strips are trimmed and sanded level. Being real timber, slivers accept oil or lacquer like the surrounding boards. It is labour-intensive, so it is priced higher than resin filling.
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. 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. It is a normal characteristic of timber floors rather than a fault in the work. That is why gap filling is excluded from our service guarantee, which covers the sanding and finishing we carry out. We make sure you know this before any filling is booked.
Helping filler last longer
Try to keep humidity and temperature reasonably stable.
Fix loose boards before filling so they move less.
Match the method to the gap size.
Insulation beneath the floor can reduce draughts and movement.
The order of work
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.
Filling at the right stage gives a much neater result than trying to fill a floor that has already been finished. It also gives us the chance to look at each gap and pick the best approach for its size and position.
Keeping the warmth in
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.
Wider gaps are better filled with slivers of reclaimed timber, which look natural and hold well.
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
If most of your gaps are narrow, resin is often the best value. Where gaps are wider than a few millimetres, slivers give a stronger, more natural finish. Plenty of floors are best treated with a combination. You can read more about our gap filling service, and we are happy to look at your boards on a free survey in Bromley.