Liquid screed: definition and characteristics

What is a liquid screed?

A liquid screed, also known as a fluid or self-leveling screed, has a consistency that allows it to be pumped and spread on its own. It does not require manual leveling: once poured, it finds its own level, requiring only a quick pass with a leveling bar to remove air bubbles.

The benefit goes beyond just convenience. With a traditional screed, flatness depends on the installer's skill. With a liquid screed, it depends on physics. The result is naturally consistent, which is crucial for large areas where correcting levels can be costly.

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The two types of liquid screed

The two are often confused, which can have real-world consequences on the job site.

• The anhydrite screed, based on calcium sulfate. Highly fluid with almost zero shrinkage, it is excellent for embedding underfloor heating pipes. It is sensitive to prolonged moisture, which requires specific precautions in wet rooms.
• The cement-based fluid screed. It covers the same applications with much better water resistance, generally at a higher cost.

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Why it is the standard for underfloor heating

Underfloor heating works best when the pipes are completely encased. Any air gap around a pipe creates thermal resistance that hinders heat transfer to the room.

A traditional screed, packed by hand, almost always leaves air pockets under the loops. A liquid screed infiltrates everywhere by gravity and eliminates this issue. This is the technical reason why it has become the standard for this type of installation, as detailed in our guide on screeds and underfloor heating.

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Its constraints

The formwork must be perfectly watertight: a liquid screed will seep through the smallest gap and end up on the floor below. The perimeter strips must be installed and secured before pouring, without any gaps. And the drying process follows its own rules: fast on the surface, much slower deep down, which makes checking residual moisture essential before laying the flooring.

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Liquid screed or traditional screed?

Traditional screed remains more economical, more forgiving on uneven surfaces, and easier to install on small areas or in sloped configurations.

Liquid screed takes the lead whenever there is underfloor heating, a large continuous surface area, a high requirement for flatness, or limited available height. The full comparison is detailed in our article traditional screed vs. anhydrite liquid screed.