At the Rhineland Regional State Association’s archive, anhydrite screed formulated with Bayer Anhydritbinder AB 20 from Bayer Chemicals AG was laid accurately up against metal rails for a sliding shelving system – with virtually no joints and no level discrepancies or riding up.
Anhydrite screed offers numerous benefits. A particularly important one for the floor covering industry is that the edges do not ride up and large areas can be laid with virtually no joints. These properties were used to positive effect in the Rhineland Regional State Association's building project at the abbey in Brauweiler near Cologne. The screed here had to be laid exactly five millimetres below the metal rails for a sliding shelving system, as the top surface, a rubber coating, had to be flush with the upper edge of the rails. Unevenness caused by the screed riding up and level discrepancies at the joints, inevitable with a cement screed, would subsequently have prevented the filing cabinets sliding smoothly.
Stanislaus Lampret of Kürten in the Rheinisch-Bergisch district, a specialist screed laying company of 30 years' standing, used its experience to persuade the building owners to use conventional anhydrite screed formulated with the binder Bayer Anhydritbinder AB 20 from Bayer Chemicals AG of Leverkusen instead of the planned cement screed.
Around 1,600 square meters of screed were laid in the Rhineland Regional State Association's archive in the abbey. Twelve 20-meter-long rails divide this surface up into 1.5-meter-wide strips; the conventional anhydrite screed was applied over the whole length without a joint and so that it lay accurately against the rails.
Large interconnected surfaces can be laid without joints primarily due to the fact that conventional anhydrite screed swells and shrinks by less than 0.1 millimetre per meter. Moreover, its thermal expansion coefficient is well below the comparable figure for cement-based screeds. It is around the same as for ceramic tiles. Consequently, hot screeds formulated with the anhydrite binder, for example, can also be laid over large surfaces without joints. Structural joints are the only ones to contend with.
Crystallization of anhydrite screeds does not cause the edges to ride up, unlike with cement screeds. A cement screed, where sizeable areas require a large number of joints, can exhibit level discrepancies of up to two centimetres. The rising and sinking problems inevitable with cement screeds can be avoided with a conventional anhydrite screed. In addition, the material exhibits high strength and good drying properties.