What floor levelling is and when it is used

Floor levelling refers to the professional correction of an existing subfloor that is uneven, wavy or contains significant height differences. Whether the base is old concrete, an anhydrite screed or a cement screed, any deviation from a flat surface can transfer directly into the final floor covering, leading to damage or visible defects.

The solution is a self levelling compound, applied in a thin layer. In most residential interiors, the maximum recommended thickness is around 2.9 centimetres, which is considered the upper limit for standard internal levelling.

Floor levelling is recommended before installing vinyl, laminate, engineered wood, carpet or tiles, wherever a perfectly flat surface is required. When removing an old floor, unexpected height differences between rooms, adhesive residues or small depressions are often revealed. In these cases, levelling becomes unavoidable.

Industry experience shows that even in new builds, height deviations of up to 1.5 centimetres over a 2-metre length are not uncommon. This exceeds the tolerance limits of most flooring systems, which is why levelling is advisable even on new screeds.

With underfloor heating, floor flatness also plays an important role in energy efficiency. A level surface ensures even heat distribution and prevents cold spots. It also supports the correct function of click-lock flooring systems.

Why subfloor preparation and priming are essential

Proper subfloor preparation is the absolute foundation of successful floor levelling. It determines whether the levelling compound bonds securely or later detaches, cracks or forms hollow areas. Despite this, preparation is often underestimated or carried out incorrectly.

Before levelling, the subfloor must be solid, dry and clean, free from dust, adhesive residues, grease, paint or loose particles. These contaminants act as separation layers and prevent proper adhesion. On older substrates, light grinding or mechanical cleaning is strongly recommended.

A critical step is applying a suitable primer before floor levelling. The primer:

• strengthens the surface
  
• reduces absorbency
  
• improves adhesion of the levelling compound
  

Different primers are designed for cement-based, anhydrite or gypsum substrates. Manufacturers clearly specify the correct product and application method in their technical documentation.

Skipping the primer significantly increases the risk of debonding, cracking or blistering. These defects cannot be repaired locally and usually require complete removal of the levelling layer, resulting in additional time and cost.

Subfloor preparation also includes moisture testing, especially in new buildings. Cement screeds should generally not exceed 2 percent residual moisture. Higher moisture levels can cause delayed drying, internal stress and surface failure.

Practical tip: If you are unsure whether the subfloor is dry enough, tape a piece of plastic sheet tightly to the floor and leave it for 24 hours. If condensation appears underneath, the subfloor is not yet ready.

How floor levelling is carried out

Floor levelling is a technically precise process that requires correct timing, suitable tools and strict adherence to installation guidelines. Although it may appear simple, attention to detail is essential.

After preparation and priming, the self levelling compound is mixed with water according to the manufacturer’s instructions. Mixing should be done with a slow-speed drill and paddle to avoid trapping air. The mixture must be fluid but not overly thin, allowing it to spread evenly and self-level properly.

The compound is poured onto the floor, spread using a levelling rake or trowel, and then deaerated with a spiked roller to remove air bubbles. This step is particularly important for thicker layers.

An edge expansion strip must be installed around the perimeter of the room. This allows the material to expand and contract with temperature and humidity changes, preventing cracks and sound bridges. The strip is installed before pouring and later concealed by skirting boards.

Material consumption is typically around 1.5 to 1.7 kilograms of dry mix per square metre at a thickness of 1 centimetre. At the maximum thickness of 2.9 centimetres, consumption can reach approximately 5 kilograms per square metre. These figures are essential for accurate cost planning.

For larger areas, it is advisable to hire professional contractors who use mixing and pumping equipment. This ensures a uniform surface without visible joints and allows precise transitions between rooms with different heights or substrates.

Although the surface may feel dry after a few hours, most manufacturers recommend waiting 24 to 72 hours before installing the final floor covering. With underfloor heating systems, the waiting period may be longer.

Ideal conditions for floor levelling are temperatures between 15 and 25 degrees Celsius and a maximum relative humidity of around 65 percent. Deviations from these conditions can negatively affect the final result.

How much floor levelling costs and what affects the price

The cost of floor levelling is not based solely on the size of the area. Several factors influence the final price:

• type and condition of the existing subfloor
  
• required thickness of the levelling layer
  
• quality of the levelling compound
  
• accessibility of the space
  
• additional work such as priming, edge strips and laser levelling
  

The greater the unevenness, the higher the material consumption and labour input. While professional floor levelling represents an additional cost, it is a long-term investment that protects the entire flooring system and prevents expensive repairs in the future.

Note: Prices are indicative and may vary depending on location, the specific contractor or the scope of work.

Even though floor levelling may seem like an “unnecessary” expense at first, investing in high-quality levelling can save you hundreds of pounds in the future. If a floor covering is installed on an uneven surface, it may begin to lift, crack or cause click joints to separate over time. In such cases, warranty claims are usually rejected because the issue is caused by an improperly prepared subfloor.

Customers often compare the cost of DIY work with professional installation. While doing it yourself may appear cheaper initially, real-world experience often shows the opposite. Poor-quality compounds, incorrect procedures or unsuitable conditions frequently result in the need to redo the entire floor.

It is always advisable to request a no-obligation quote with a detailed breakdown of all items. This allows you to compare services properly and ensures that you are paying for actual workmanship, not just a price per square metre.

Common floor levelling mistakes and how to avoid them

Floor levelling can appear deceptively simple. Pour the compound, spread it and the job is done. In practice, however, this seemingly simple step is one of the most commonly disputed stages in flooring work. Mistakes during subfloor preparation, priming or levelling itself can damage even the most expensive floor coverings.

One of the most serious mistakes is skipping the subfloor primer. Many people assume that sweeping or vacuuming the surface is sufficient, but this is not the case. Without proper priming before levelling, the compound may fail to bond to the substrate. This can lead to delamination, air bubbles or even complete detachment of the levelling layer. Even concrete that appears dry can contain residual moisture, which may later cause problems under laminate or vinyl flooring.

Another frequent issue is incorrect or incomplete installation of the perimeter expansion strip. Some installers omit it entirely, while others install it only in visible areas. The result is the same. When temperatures change, the floor cannot expand properly, presses against the walls and causes cracks, lifting or sound bridges. The expansion strip must be installed continuously around the entire perimeter of each room to function correctly.

Incorrect mixing of the levelling compound is another common error. Adding too much water or insufficient mixing leads to uneven drying, reduced strength and cracking. Using the correct tools, such as a mixing paddle, spiked roller and trowel, and strictly following the manufacturer’s mixing ratios is essential.

Drying time is also often underestimated. Many people install the final floor covering before the compound has fully cured. This can result in surface damage, deformation and a significantly reduced lifespan of the floor. A minimum waiting time of 48 hours should always be observed, or longer depending on the product used and site conditions.

Based on the experience of professional floor installers, experimenting with critical preparation steps is not recommended. It is far more sensible to consult a specialist or entrust the work to a company with proven experience. Companies such as NUMIQ work in accordance with applicable technical standards and follow all required procedures, ensuring a durable and reliable result.

Do you really need levelling, or is there another way to level your floor?

Not every uneven floor requires a self-levelling compound. Although floor levelling is the most common solution for minor height differences, other methods may be more suitable in specific situations.

If the subfloor has larger height differences, for example 3 centimetres or more, a dry floor levelling system may be a better option. This typically involves OSB boards, gypsum fibre boards or complete dry screed systems installed over a levelling fill. The advantages include fast installation without drying time and minimal load on the structure, making it ideal for refurbishing older buildings.

The type of final floor covering also plays a key role.

• Vinyl and laminate require an extremely flat surface, otherwise the floor may bend or lift.
  
• Carpet can tolerate minor unevenness.
  
• Tiles require a rigid and highly stable base.
  

In some older properties, a combined approach is used, such as levelling compound in the centre of the room and levelling boards along the edges. Choosing the right method depends on the specific conditions, including height differences, substrate condition, moisture levels and expected load.

Building specialists recommend a professional inspection before making a decision. During this process, height differences are measured accurately using levelling equipment, providing a clear overview of available options and allowing a realistic comparison between wet and dry levelling systems.

The advantage of working with professionals:
They recommend a solution tailored to your home, not necessarily the most expensive one, but the most suitable.

Why it is better to leave floor levelling to professionals and how to choose the right contractor

Although floor levelling may seem like a task suitable for a skilled DIY enthusiast, reality often proves otherwise. Proper subfloor levelling is technically demanding, and every detail affects whether the finished floor lasts for decades or starts failing after just a few months.

Professional contractors have not only the right tools but also the experience to avoid common mistakes. They can accurately determine the required thickness, select the correct primer, install expansion strips properly and account for the specific characteristics of the building, from moisture levels to structural details.

Professional installation also offers:

• faster completion, often within one to two days
  
• a workmanship guarantee, which DIY work does not provide
  
• technical documentation that can be useful in the event of a flooring warranty claim
  

When choosing a flooring contractor, consider the following:

• Check customer reviews and previous projects.
  
• Request a detailed quotation with a clear breakdown of tasks such as priming, levelling, expansion strips and drying times.
  
• Verify that the company follows recognised technical standards and uses quality materials.
  
• Ask about timelines, warranty coverage and how complaints are handled.
  

The result:
A flat, stable and professionally prepared floor that forms the perfect foundation for tiles, vinyl or laminate flooring.