Screed is the levelling layer applied over a structural floor slab on which the final floor finish — wood, tiles or carpet — is laid. In German-speaking countries it is called Estrich; in the Netherlands “dekvloer” or “afwerkvloer”. Screed serves several functions and is a key part of any modern floor build-up.
Functions of a screed
The screed performs several tasks:
- Levelling — making the rough slab flat
- Load distribution — spreading point loads
- Acoustic insulation — when laid as a floating screed
- Heat conduction — with underfloor heating
- Substrate — base for the final floor finish
Types of screed
| Type | Binder | Application |
|---|---|---|
| Sand-cement screed | Portland cement | General use, dwellings, commercial |
| Anhydrite screed | Calcium sulphate | Underfloor heating, fast drying |
| Magnesium screed | Magnesium oxide | Industrial, sometimes heritage |
| Asphalt screed | Bitumen | Industrial floors |
| Resin screed | Epoxy, PUR | Industrial, chemical-resistant |
Forms of installation
Bonded screed
The screed is laid directly onto the slab and bonds to it. Quickest solution, thinnest build-up (from 25 mm).
Floating screed
The screed rests on an insulation layer (rigid insulation or acoustic insulation) without contact with the walls or slab. Requires:
- Minimum 35-50 mm thickness
- Perimeter edge strip along all walls
- Shrinkage reinforcement (mesh or fibres)
Advantage: better acoustic insulation and suitability for underfloor heating.
Screed on separating layer
A separating membrane sits between the screed and the slab. The screed can shrink independently without cracking the finish.
Screed and underfloor heating
For underfloor heating, anhydrite screed is popular because it:
- Dries faster (around 1 cm per week vs. sand-cement)
- Conducts heat better
- Shrinks and cracks less
- Self-levels for a flatter result
The heating may only be commissioned after a rest period (often 7 days), with a gradual temperature increase to dry the screed.
Application rules
- Prepare the substrate — clean, level, strong enough
- Place edge strips along all walls and columns
- Plan movement joints for large areas (>40 m²)
- Mix and lay — observe the minimum thickness
- Compact and finish — sand-cement often machine-finished
- Curing and drying — sand-cement at least 28 days, anhydrite faster
- Moisture testing before laying the floor finish
Related terms
- Floor build-up
- Anhydrite screed
- Underfloor heating
- Acoustic insulation
- Levelling layer
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