Why is subfloor preparation for floating flooring so important?

Subfloor preparation is a fundamental stage that directly influences durability, appearance and comfort underfoot. An uneven or unsuitable subfloor causes movement, noise and excessive stress on the locking systems of the floor panels.

As a general guideline, deviations in level should not exceed approximately 2 mm over a 2 metre length. A common misconception is that floating floor installation is the first step of the job. In reality, it is the final stage of a much longer preparation process. If the subfloor is neglected, even high-quality flooring will develop problems over time.

How to check the condition of the existing subfloor?

The first step is a thorough assessment of the existing subfloor. With concrete subfloors, check that the surface is dry, sound and free from cracks or loose material. In older buildings, concrete is often uneven and requires levelling with a self-levelling compound.

If the floating floor is being installed over existing timber flooring or parquet, the boards must be firmly fixed, stable and free from movement or squeaking. Levelness should be checked using a spirit level or laser level. Any deviations beyond acceptable limits must be corrected to prevent damage to the locking joints.

Moisture levels must also be checked carefully. Excess moisture in concrete subfloors is one of the most common causes of later floor deformation.

What does sanding and levelling the subfloor involve?

If uneven areas or surface defects are identified, sanding and levelling the subfloor becomes essential. The aim is to create a perfectly flat surface suitable for laying underlay and flooring.

On concrete subfloors, self-levelling compounds are commonly used. Before application, the surface should be sanded to remove contamination and improve adhesion. Skipping this step often results in raised areas or uneven joints between floor panels.

The cost of levelling depends on the condition of the subfloor and the scope of work required. Accurate pricing is best determined after an on-site inspection.

Which underlay should be used under a floating floor?

Underlay beneath floating flooring performs several important functions. It improves acoustic insulation, compensates for minor imperfections and protects the locking system from wear. Available options include PE foil, foam underlays and rigid XPS boards.

The choice depends on the type of subfloor and the room’s intended use. For concrete subfloors, a vapour barrier is essential to prevent moisture transfer. Combined underlays are also available, integrating sound reduction and moisture protection in one product.

Why is floor acclimatisation essential?

Acclimatisation means storing the flooring packs in the installation room for at least 48 hours before laying. This allows the material to adapt to room temperature and humidity, reducing the risk of expansion or contraction after installation.

Flooring should only be installed under stable indoor climate conditions. Ignoring acclimatisation often leads to deformation that cannot be claimed under warranty. Packs should be stored flat and left unopened until installation.

What is an expansion gap and why must it not be ignored?

An expansion gap is the space left between the floor and surrounding walls to allow for natural movement of the material. This gap is typically between 10 and 15 mm and must be maintained around the entire perimeter of the room.

Expansion gaps prevent the floor from lifting or buckling. The same clearance is required around fixed elements such as pipes, columns and door frames. These gaps are later concealed using skirting boards to achieve a clean, finished appearance.

How much does professional installation including preparation cost in the UK?

The cost depends on several factors, including the condition of the subfloor, the extent of preparation work, the flooring type and the location. The installation of floating flooring itself is generally priced at a lower level, but levelling or sanding work can significantly increase the total cost.

The most accurate way to determine the final price is through an individual quotation following a professional site assessment.

What do you gain from thorough subfloor preparation?

Preparing the subfloor properly is not just a technical step but an investment in the quality and longevity of the entire floor. A level and dry concrete base, correct acclimatisation, suitable underlay and properly maintained expansion gaps ensure a stable, quiet and visually consistent floor.

Thorough preparation helps avoid common issues such as panel lifting, squeaking and premature wear of locking systems. A professional approach saves money in the long term and delivers a floating floor that performs reliably for many years.