How to Fix Gaps Between Timber Floorboards

Gaps in timber floorboards are one of the most common flooring issues homeowners across Sydney experience. In some cases, they’re completely normal. In others, they can point to moisture problems, poor installation, or structural movement beneath the floor.

The challenge is knowing the difference.

Small seasonal gaps are often harmless, but larger or permanent gaps can affect the appearance, comfort, and even the longevity of your timber flooring. The good news is that most gaps can be repaired successfully when the underlying cause is identified properly.

In this guide, we’ll explain why gaps in timber floorboards occur, when they actually need fixing, and the most effective repair methods used in Sydney homes today.

Why Do Gaps Appear in Timber Floorboards?

Timber is a natural material that constantly reacts to changes in moisture and temperature.

As humidity rises, timber absorbs moisture and expands. When conditions become drier, the timber contracts. This natural movement is the most common reason gaps appear between floorboards.

In Sydney, seasonal humidity changes can be significant, especially between humid summers and drier winters. Because of this, some movement in timber flooring is completely normal.

However, seasonal expansion and contraction aren’t the only causes of floorboard gaps.

Common Causes of Gaps in Timber Floorboards

Poor Acclimatisation Before Installation

Timber flooring should always be allowed to acclimatise to the indoor environment before installation.

If boards are installed too soon, they may shrink after laying, creating permanent gaps as they adjust to the home’s moisture conditions.

Subfloor Problems

Uneven or unstable subfloors can cause timber boards to shift over time.

In older Sydney homes, common issues include:

• Poor ventilation beneath the house
• Moisture build-up
• Deteriorating joists
• Uneven bearers or supports

These problems can lead to movement throughout the flooring system, causing wider or inconsistent gaps.

Natural Ageing and Wear

Over decades, timber floors naturally shift, settle, and wear.

Homes in older Sydney suburbs such as Balmain, Paddington, and Newtown often develop more noticeable gaps simply due to the age of the flooring and the movement of the building over time.

Incorrect Installation Methods

If the floorboards weren’t fixed properly during installation — whether through insufficient nailing, poor adhesive application, or incorrect spacing — boards may gradually separate over the years.

When Do Gaps Actually Need Repair?

Not every gap needs to be fixed.

In fact, trying to fill seasonal gaps can sometimes make the problem worse.

Seasonal Gaps

Small hairline gaps that appear during winter and close naturally during humid months are usually normal. Filling these gaps with rigid materials can create pressure when the timber expands again, potentially leading to:

• Buckling
• Cracking
• Peaking boards
• Filler failure

Gaps That Need Attention

You should generally consider repairs when gaps:

• Remain open year-round
• Are wider than 2–3mm
• Allow draughts through the floor
• Trap dirt and debris
• Affect comfort or insulation
• Appear suddenly or continue worsening

If the floor feels uneven, soft, or unstable underfoot, the issue may extend beyond cosmetic gaps and require a professional inspection.

Best Methods for Fixing Gaps in Timber Floorboards

The right repair method depends on:

• Gap size
• Timber species
• Floor condition
• Whether movement is seasonal or permanent

Here are the most common solutions.

1.⁠ ⁠Flexible Gap Fillers

For small gaps, flexible timber fillers or specialised caulking products are often the easiest and most cost-effective solution.

These fillers are designed to move with the timber rather than cracking as the boards expand and contract.

They’re commonly used for gaps up to around 2mm wide.

Benefits

• Affordable
• Quick to apply
• Flexible movement
• Available in timber colours
• Suitable for DIY repairs

Many products can be colour-matched to Australian hardwoods such as:

• Blackbutt
• Spotted gum
• Tallowwood
• Brush box

Once applied, the filler can usually be lightly sanded and finished to blend with the surrounding floor.

2.⁠ ⁠Timber Slivers or Timber Wedges

For larger gaps, timber slivers provide a more durable and visually seamless repair.

This method involves cutting thin strips of matching timber and gluing them into the gaps between boards.

Once the adhesive cures, the slivers are sanded flush with the floor surface.

Best For

• Gaps between 3–10mm
• Older timber floors
• Heritage restorations
• Permanent gap repairs

When done correctly, timber slivers blend naturally into the flooring and deliver a long-lasting result.

Matching the timber species and grain pattern is essential for a professional finish.

3.⁠ ⁠Rope or Hemp Gap Filling

A more traditional repair method involves inserting natural rope or hemp cord into the gaps.

This technique is still popular in heritage homes because it preserves the original character of older timber floors.

The rope is typically:

• Stained to match the timber
• Pressed firmly into the gap
• Sealed into place

Advantages

• Flexible movement
• Traditional appearance
• Reversible repair method
• Ideal for period homes

This method is commonly used in heritage-listed Sydney properties where maintaining authenticity is important.

4.⁠ ⁠Re-Cramping and Re-Laying Floorboards

If the gaps are extensive or the boards have shifted significantly, the most effective solution may be to lift and re-lay the floorboards.

This process is known as re-cramping.

The boards are carefully removed, tightened together using specialised clamps, and then re-fixed to the joists with correct spacing restored.

Any remaining gap at the perimeter is filled using new matching boards.

Best For

• Severe floor movement
• Large widespread gaps
• Structural floor restorations
• Older timber homes

This is a labour-intensive professional repair, but it provides the most complete long-term solution.

5.⁠ ⁠Sanding and Refinishing

Gap repairs are often combined with floor sanding and polishing to restore the entire floor surface.

After gaps are filled, the floor is:

• Sanded smooth
• Levelled evenly
• Refinished with protective coatings

Popular finishing options include:

• Water-based polyurethane
• Oil-based polyurethane
• Hardwax oil finishes

Sanding and refinishing help blend repairs seamlessly into the surrounding floorboards for a cleaner, more uniform appearance.

How to Prevent Gaps from Returning

Repairing the gaps is only part of the solution. Preventing future movement is equally important.

Maintain Stable Indoor Humidity

Timber floors perform best when indoor humidity remains relatively stable.

Large fluctuations caused by:

• Air conditioning
• Heating systems
• Poor ventilation
• Excess moisture

can all increase timber movement.

A hygrometer can help monitor indoor humidity levels throughout the year.

Improve Subfloor Ventilation

Poor airflow beneath the home is a major contributor to timber movement.

Make sure subfloor vents remain:

• Clear of debris
• Unblocked
• Adequately sized

Good ventilation helps prevent excess moisture build-up beneath the flooring.

Avoid Excess Water

Timber floors should never be soaked during cleaning.

Instead:

• Use a lightly damp microfibre mop
• Clean spills immediately
• Avoid steam mops
• Avoid excessive wet mopping

Too much moisture can cause swelling, movement, and long-term floor damage.

Protect the Floor from Movement

Use felt pads beneath heavy furniture to reduce pressure points and minimise shifting over time.

When to Call a Professional

While minor cosmetic gaps can often be repaired yourself, larger or widespread gaps should be assessed professionally.

You should contact a flooring specialist if:

• Gaps continue growing
• Boards feel loose or unstable
• The floor squeaks excessively
• You suspect moisture issues
• The subfloor may be damaged
• The floor feels uneven or bouncy

A professional timber flooring contractor can identify underlying issues such as:

• Subfloor movement
• Moisture ingress
• Structural settling
• Termite damage
• Installation defects

before recommending the most suitable repair method.

Final Thoughts

Gaps in timber floorboards are a normal part of owning timber flooring, especially in Sydney’s changing climate. However, understanding whether those gaps are seasonal, cosmetic, or structural is the key to choosing the right repair approach.

From flexible fillers and timber slivers to full floor re-cramping, there are effective solutions available for almost every situation.

If your timber floors are starting to show signs of age, movement, or wear, addressing the problem early can help preserve both the appearance and lifespan of your flooring for many years to come.