Gap Filling: Resin or Timber Slivers?
The two main methods, and why gaps can return
Gaps between floorboards are especially common in older homes, where boards have shrunk and moved over many decades. They let in cold draughts from under the floor, trap dust and crumbs, and can make an otherwise beautiful floor look tired. 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. It is spread across the floor, worked into every gap and sanded smooth once it has hardened. It is ideal for narrow gaps, small cracks, splits and nail holes.
Good colour match because it uses your floor's own dust.
Quick and cost-effective across a whole room.
Best for gaps of a few millimetres.
Can crack or fall out as boards expand and contract.
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. Because the slivers are wood, they take the finish in a similar way to the floor and can look very natural. The work is slower and more skilled, so it costs more than resin.
Seasonal and structural movement
This is the part many people do not expect: wooden floors are never completely still. Timber absorbs moisture in humid summer months and releases it when the heating is on in winter, so boards swell and shrink with the seasons. 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. That is why 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
Try to keep humidity and temperature reasonably stable.
Fix loose boards before filling so they move less.
Choose slivers for wider gaps; resin for fine cracks.
Insulation beneath the floor can reduce draughts and movement.
The order of work
Gap filling is normally carried out as part of a full sanding and finishing project, rather than on its own. We begin by sanding the floor to level the boards and strip off the old coating. 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.
Keeping the warmth in
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. 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.
That natural movement is the reason gap filling is not covered by our service guarantee.
Securing loose boards, keeping humidity steady and ventilating the void below help the filling last.
Choosing a method
If most of your gaps are narrow, resin is often the best value. For wider gaps, slivers tend to look better and hold up better. Many floors benefit from a mix of both. You can read more about our gap filling service, and we are happy to look at your boards on a free survey in Esher.