Gap Filling: Resin or Timber Slivers?
The two main methods, and why gaps can return
Most period floors develop gaps over the years as boards dry, shrink and shift. 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.
Filling with resin
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 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.
Best for gaps of a few millimetres.
May crack when the floor moves with the seasons.
Method two: timber 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. 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.
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.
Because of this, any gap filler, resin or timber, can crack, shrink, loosen or work out over time. 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, which covers the sanding and finishing we carry out. We make sure you know this before any filling is booked.
Tips for better results
Keep indoor humidity steady and avoid extreme heating swings.
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.
When gaps are filled
In most cases, gaps are filled during a floor restoration, not as a separate job. We begin by sanding the floor to level the boards and strip off the old coating. After that, gaps are cleaned and filled, and the floor is sanded again once everything has set. 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 allows us to check each gap closely and choose the right method for it, rather than treating the whole floor the same way.
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.
In summary
Resin filler made with dust from your own floor suits fine gaps, small cracks and holes best.
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.
Because of this natural movement, gap filling is excluded from our service guarantee.
Stable heating, secure boards and good ventilation under the floor all help filler last longer.
Choosing a method
For floors with mostly narrow gaps, resin is usually the practical, affordable choice. For wider gaps, slivers tend to look better and hold up better. Many floors benefit from a mix of both. Find out more about our gap filling service, or ask us to assess your boards during a free survey in Kingston.