Anhydrite screed: what is it?

Industrially prepared in a power plant concretethe anhydrite mortar is delivered by mixer truck to be poured in place. L’application is carried out mechanically (at the pump) over a thickness of 3 to 6 cm. But it is possible to compensate occasionally for differences in level of 7 or 8 cm. The process ensures rapid implementation. However, a certain amount of mixture must be ordered in order for the cost of delivery to be profitable. Asked price: between 20 and 25 € / m², for a minimum area of ​​100 m².

Minimal shrinkage, but slow drying

A screed fluid at mortar of cement dries quickly, but shrinks significantly. It is necessary to put in place splitting joints to avoid cracking of the flooring glued (standard NF EN 13813). The anhydrite screed removes its water very slowly, which significantly reduces shrinkage. The drying time is on average one week per centimeter of thickness, up to 4 cm. Beyond that, it takes about two weeks. The ambient temperature and the ventilation of the room influence the final drying.

At one point, the anhydrite screed becomes dry on the surface while retaining a moisture content higher than the value allowed in the core.technical advice (AT) mortar. As a general rule, the installation of the covering cannot intervene above 1 to 0.5% of residual humidity, according to the material (floor tile, parquet, vinyl…).