How to Keep Your Solid Wood Floors Flat, Tight, and Flawless

Solid wood flooring is a timeless and elegant choice, but like any natural material, it responds to changes in its environment. Two of the most common issues homeowners face are gaps between floorboards and cupping — a warping effect that causes the edges of the boards to rise above the centre.

These problems can often be traced back to preventable mistakes during or before installation. Fortunately, by understanding the causes and taking a few key precautions, you can protect your investment and enjoy a beautiful, stable wood floor for years to come.

What Causes Gaps and Cupping in Solid Wood Floors?

Solid wood flooring is a living material — it expands and contracts in response to changes in temperature and humidity. When conditions aren’t properly managed before or after installation, visible issues like gaps and cupping can develop. Here are the most common culprits:

• Seasonal Humidity Changes: Wood naturally shrinks in dry winter air and expands in humid summer months. Without humidity control, this can lead to separation or distortion.
• Lack of Acclimatisation: If boards are installed without adapting to the room’s environment, they may shift significantly after installation.
• Moisture from Subfloors: Damp concrete or unsealed subfloors can introduce excess moisture into the wood, causing it to swell and cup.
• Poor Installation Practices: Failing to leave adequate expansion gaps or using the wrong fixing method can trap the wood and force it to warp.
• Inconsistent Indoor Climate: Homes without proper humidity control can create unstable conditions that lead to long-term flooring issues.

Acclimatisation: The First Step to Prevention

One of the most critical steps in preventing gaps and cupping is proper acclimatisation. Solid wood flooring should never be installed immediately after delivery. Instead, it needs time to adjust to the temperature and humidity of its new environment.

We recommend storing the flooring in the room where it will be installed for at least 7 to 14 days before installation. The boxes should be opened and the planks spread out or stacked loosely to allow air circulation. This helps the wood reach a moisture content balance with the indoor environment, reducing the risk of expansion or contraction after fitting.

Skipping this step is one of the most common causes of future movement in the boards — and one of the easiest to avoid.

Subfloor Preparation & Moisture Testing

A stable and dry subfloor is essential for the long-term performance of solid wood flooring. Moisture rising from below — especially in concrete substrates — can cause the timber to absorb excess humidity, leading to cupping, swelling, and eventual damage.

Before installation, always carry out a moisture test using a reliable moisture meter. For timber subfloors, the moisture content should typically be below 12%, and for concrete, below 4%. If moisture levels are too high, the subfloor must be allowed to dry or be treated with a suitable DPM (damp proof membrane).

Levelness is another important factor. A subfloor that is uneven can put stress on the boards over time and lead to movement. Levelling compounds or appropriate underlay systems should be used where needed to create a flat, even surface.

Proper Installation Techniques

Even with a perfectly acclimatised floor and a dry subfloor, poor installation can still lead to gaps and cupping. That’s why it’s essential to follow best practices — or trust a professional with experience in solid wood fitting.

• Leave the Right Expansion Gaps: Solid wood needs room to move. Always leave a minimum 10–15mm expansion gap around the perimeter of the room and around fixed objects like pipes or door frames.
• Choose the Right Fixing Method: Nail-down installation is often preferred for solid wood. It provides stability while allowing some natural movement. In certain cases, full-spread adhesive may be used, but only on the right subfloor type.
• Use the Correct Tools and Spacing: Spacers, tapping blocks, and flooring nailers ensure secure placement and reduce the risk of uneven tension between boards.

Correct installation sets the foundation for a stable, long-lasting floor. Skipping or rushing steps often leads to problems that could have been easily avoided.

Controlling Indoor Humidity After Installation

Once your solid wood floor is installed, the job isn't over — maintaining the right indoor climate is key to preserving its condition. Wood continues to react to the environment even after installation, so it’s essential to keep relative humidity between 40% and 60% throughout the year.

In winter, central heating can dry the air, causing the boards to shrink and form gaps. In summer, high humidity can make the boards expand and cup. To avoid this seasonal movement:

• Use a humidifier during dry months to add moisture to the air.
• Use a dehumidifier or air conditioning during humid months.
• Monitor humidity with a hygrometer to stay within the recommended range.

By taking these small but important steps, you can dramatically reduce the risk of movement and extend the life of your solid wood flooring.

Signs of Trouble: When to Act

Even with careful planning, changes in the environment or minor installation issues can still cause problems over time. Catching these early makes a big difference in preventing long-term damage or costly repairs. Here’s what to watch out for:

• Gaps Between Boards: Small gaps may appear during dry seasons, but large or uneven gaps could signal ongoing moisture imbalance or poor installation.
• Cupping: The edges of boards rise above the centre, often caused by moisture from below. If left untreated, it can worsen and affect the stability of the floor.
• Movement Underfoot: Boards that shift, creak excessively, or feel unstable may point to loose fixing or subfloor issues.

If you notice any of these signs, it’s best to consult a professional flooring specialist. Early intervention can often prevent a full replacement and restore the floor’s condition.

Explore Our Solid Wood Flooring Ranges

If you're planning to install solid wood floors, choosing high-quality materials is the first step to long-term satisfaction. We offer a wide selection of solid wood flooring options in a variety of styles, finishes, and thicknesses — all suitable for professional installation with proper preparation.

Our range includes trusted brands and natural finishes to suit traditional and contemporary interiors alike. Whether you're looking for rich oak tones or elegant natural planks, you'll find quality you can depend on.

Conclusion

Preventing gaps and cupping in solid wood floors starts with the right approach — from acclimatising the boards and preparing the subfloor, to controlling humidity after installation. These steps may seem small, but they make a big difference in protecting your floor’s appearance and structure over time.

By following best practices and investing in quality materials, you can enjoy the natural beauty of solid wood flooring without surprises. Browse our solid wood flooring collection today or get in touch if you need help choosing the right product for your space.