Gaps between old floorboards are common, particularly in period properties. The question is whether to fill those gaps when sanding and restoring the floor.
The answer depends on the size and consistency of the gaps, the condition of the timber and whether the floor is still moving.
Sometimes filling produces a much neater finish. In other cases, leaving the gaps alone can give a better long-term result.
Here is what you need to consider before deciding.
Why do wooden floors have gaps?
Wood will naturally expand and contract as moisture levels and conditions inside a property change. Over many years, this movement can leave visible gaps between floorboards.
Older floors can also have nail holes, damaged areas, previous repairs and other small imperfections.
Some of these will already be visible. Others may only become obvious once the old finish has been removed during wood floor sanding and restoration.
That is why we normally assess the floor’s condition before deciding what to fill. A gap that looks unsightly does not automatically mean filler is the right answer.
Should gaps between wooden floorboards be filled?
Small, reasonably consistent gaps can often be filled successfully.
One method is to mix a specialist resin with fine sanding dust collected from the floor. Using dust from the same timber helps the repair blend more naturally with the surrounding boards.
For gaps of around 2–3mm, this can work particularly well. The filler can penetrate the gap, adhere to the sides, and dry relatively quickly.
Gaps up to approximately 6mm may also be suitable in some circumstances, although they usually need more drying time before the floor can be sanded again.
The key point is that you shouldn’t fill every gap.
If a floor has consistent gaps throughout, particularly an older floor that naturally moves with changes in humidity, leaving those gaps may produce a better long-term result.
Why can wood floor filler fall out?
Wooden floors move.
The timber responds to changes in moisture and humidity throughout the year. If filler is placed into a gap that continues to open and close, the movement can eventually loosen it.
That is why filling every visible gap isn’t always the best approach.
A freshly filled floor might initially look very uniform. If sections of filler begin to loosen later, however, the result can become patchy and more noticeable than the original gaps.
Before filling inconsistent or unusual gaps, it is also worth considering why they are there. Moisture readings can help determine whether floor movement is linked to moisture beneath or around the timber.
A professional assessment as part of a wood floor restoration can help determine whether filling is appropriate before refinishing.
What about holes and other imperfections in the floor?
Holes need slightly different treatment.
You can repair larger holes with a specialist two-component, fast-setting wood filler. One advantage is the relatively short setting time, which allows restoration work to continue without a lengthy wait.
There is a compromise, though: colour matching.
A manufactured filler will not always match the surrounding timber perfectly. On a floor with plenty of natural grain and variation, a darker repair can sometimes blend in and look similar to a knot.
On pale, evenly coloured timber, the same repair can be much more noticeable.
As holes and damaged areas grow, replacing the affected section or board may give a better result than adding more filler.
Can sanding dust and resin be used to fill holes?
For smaller holes and gaps, resin mixed with fine sanding dust from the existing floor can provide a closer colour match.
Because the dust comes from the floor itself, the repair tends to sit more naturally alongside the surrounding timber.
However, this method has limits. Larger or deeper holes may prevent the resin filler from setting properly, so you may need a different repair method. The right choice will usually depend on the size of the repair, the type of timber and how noticeable the filled area is likely to be once the finish has been applied.
When would we normally recommend filling a wooden floor?
Filling is worth considering where there are small, uneven or inconsistent gaps that interrupt the appearance of an otherwise sound floor.
We may also recommend filling individual holes or damaged areas where the repair can blend naturally with the timber.
The decision becomes more cautious when:
- gaps are wide throughout the floor
- the boards are still moving
- moisture may be contributing to the movement
- the filler is unlikely to stay securely in place
- the colour difference would make the repair more obvious
- replacing a damaged board would produce a better finish
The aim is not to remove every sign of age from an old wooden floor. It is to make sensible repairs that improve the finished floor and have a good chance of lasting.
Filling gaps before oiling or lacquering a wooden floor
Gap repairs are normally part of the preparation and sanding process, before you apply the final protective finish.
The finish you choose will also make a difference to the timber’s final appearance.
An oiled wooden floor tends to retain a natural appearance, while sanding and lacquering give the floor a different type of protective finish.
If repairs are needed, consider them as part of the complete restoration rather than treating the filler as a separate job.
So, should you fill your floorboard gaps?
There is no blanket rule.
Small, inconsistent gaps: filling can often improve the finished appearance.
Small holes and imperfections: these can often be repaired successfully using an appropriate filler.
Large or consistently spaced gaps: leaving them may be the better option, particularly if the floor naturally moves.
Large damaged areas: repairing or replacing the affected timber may give a better result than filler.
Most importantly, find out why the gaps are there before filling them. If the floor is moving because of moisture or seasonal changes, filling the symptom without understanding the cause may lead to the filler coming loose later.
Get your wooden floor assessed before deciding.
Every old wooden floor is slightly different. The timber’s age, previous repairs, moisture levels, gap sizes, and the amount of natural movement all influence what we recommend.
Our team can inspect your floor and explain which gaps are worth filling, which are better left alone and whether any boards would benefit from repair or replacement.
You can get in touch with Floor Sanding Cambridge if you would like us to assess your floor.
You can also learn more about our wood floor restoration packages and the different levels of restoration available.
