Traditional screed: definition and composition

What is a traditional screed?

A traditional screed is a layer of mortar made from sand, cement and water, laid by hand and then levelled with a screed rail. It is also called a sand-cement screed. It is the oldest screed still commonly laid, and the most versatile.

What defines it is not its position on the substrate but its composition and method of installation. A traditional screed can be bonded, floating or unbonded depending on what lies beneath it.

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What is it made of?

Three components only: sand, cement as the binder, and the mixing water. The ratio between them determines the entire behaviour of the screed.

Too little cement produces a friable screed that dusts and breaks up at the surface. Too much makes it more prone to shrinkage and more likely to crack as it dries. Excess mixing water, often added to make the work easier, reduces the final strength without anything showing for several weeks.

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How is it installed?

The mortar is spread over the substrate, levelled with a rail between height markers, then floated to close the surface. Unlike a flow screed that finds its own level, flatness here depends entirely on the skill and experience of the team.

Compaction matters as much as levelling. A poorly compacted screed stays porous at depth, which weakens it and lengthens its drying time.

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What thicknesses must be respected?

In Belgium, Buildwise technical note TV 189 sets a minimum of 3 cm for an unreinforced bonded cement-based screed, and 5 cm as soon as the screed is floating or unbonded. These are minimums, not design thicknesses.

Shrinkage during drying also requires the surface to be divided. Without joints, the screed cracks where stresses concentrate, usually at re-entrant corners and in narrow passages.

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When should it be preferred over a flow screed?

Whenever water, heavy loads or a tight schedule are involved. It tolerates wet rooms and outdoor use, it carries vehicle traffic, and it is walkable within days, where an anhydrite screed needs weeks before it can receive a floor covering.

It does give way on flatness and on thermal performance with underfloor heating. Our screed laying services cover both families depending on the configuration of the site.