How to Fill Gaps in Wooden Floors

Gaps between floorboards are especially common in older homes, where boards have shrunk and moved over many decades. 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.

Method one: resin filler

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.

• Best for gaps of a few millimetres.

• Can crack or fall out as boards expand and contract.

Reclaimed wood strips

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. 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. On top of that, the building itself moves slightly, and joists flex as people walk across the floor.

Because of this, any gap filler, resin or timber, can crack, shrink, loosen or work out over time. 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, while the sanding and finishing themselves remain covered. We will always explain this before you decide.

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.

• Consider fitting insulation under suspended floors where possible.

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. 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.

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. 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.

The essentials at a glance

• 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.

• 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 Barnet.