Floor levelling: definition and purpose

What is floor levelling?

Floor levelling is a thin layer of mortar applied over an existing substrate to correct its surface defects. It makes good hollows, humps, adhesive residue or a roughness incompatible with the intended floor covering.

Its function is to prepare, not to constitute. The levelling layer follows the substrate, it does not replace it and it never corrects its structural defects.

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Where is the boundary with a screed?

On function, not on thickness, even though the two overlap. A screed constitutes a load-bearing layer, it can incorporate insulation, encase underfloor heating, be decoupled from the substrate. A levelling layer does none of that.

In practice, below 3 cm in bonded form, the threshold set by Buildwise technical note TV 189 for a cement-based screed, you are in the territory of levelling. The question to ask is simple: does the floor need to gain a function, or only a surface?

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What thickness does levelling allow?

From one to a few millimetres for common self-smoothing products, up to around one centimetre for fibre-reinforced or filled formulations. Each product has its range, stated on its technical sheet, and exceeding it invites crazing and debonding.

Trying to make good 3 cm of level difference with a levelling compound is a classic false economy. The product is expensive per square metre at those thicknesses and it is not designed to work that way.

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When is levelling enough?

When the substrate is sound, at the right level, and only flatness is missing. That is the typical case of a renovation where an old floor covering is removed to lay a new one that demands more regularity.

It is not enough as soon as height must be gained, insulation added, decoupling achieved or heating embedded. In those cases only a screed answers. See our screed laying services.