What is an Anhydrite Screed?
Anhydrite screed is a self-leveling floor screed made from calcium sulfate (anhydrite) binder mixed with water, sand, and additives. It is poured as a liquid onto a structural floor to create a smooth, flat surface that serves as the substrate for a final floor finish such as tiles, laminate, or vinyl.
How anhydrite screed is applied
Unlike traditional sand-cement screeds that are mixed to a stiff consistency and laid by hand, anhydrite screed is delivered as a fluid mixture and pumped directly onto the floor. Because it is liquid, it flows naturally into a level surface, filling gaps and producing a very flat finish with minimal manual effort.
The typical application process involves:
- Preparation — The structural floor is cleaned and a separation layer or insulation is laid down.
- Edge strips — Flexible foam strips are placed along walls to allow for thermal expansion.
- Pouring — The liquid screed is pumped through a hose and poured to the required depth, usually between 25 and 80 mm.
- Leveling — Although the screed is self-leveling, workers may use a dappling bar to help release trapped air and ensure an even surface.
- Drying — The screed must dry thoroughly before a floor finish is applied. Drying times vary depending on thickness and conditions.
Advantages
Anhydrite screed offers several benefits over traditional cement-based screeds. It can be poured much faster, covering large areas in a single day. It produces a very smooth surface that often requires no additional leveling. It also has excellent thermal conductivity, making it an ideal choice for use with underfloor heating systems, as it encapsulates the heating pipes or cables evenly and transfers heat efficiently.
Considerations
Anhydrite screed is sensitive to moisture. It must be fully dry before moisture-sensitive floor finishes are applied, and it is not suitable for wet rooms without proper waterproofing. The surface also forms a thin layer of laitance during curing that must be sanded off before applying adhesives or finishes.
Related terms
- Cement screed
- Self-leveling compound
- Underfloor heating
- Floor finish
- Laitance
- Floating screed
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