Conventional anhydrite screed proved to be the solution for the new Rewenta I and II building complex in Cologne, Germany. In the addition built for the REWE Group, screed was laid flush with underfloor ducting, covering conduit branching off from the duct. Instead of using cement screed as originally planned, the screed layer and the general contractor's project management team elected to instead use anhydrite screed because of its superior shrinkage and deformation characteristics. The Burger Group of Kürten, Germany, laid a total of 25,000 square metres of conventional anhydrite screed formulated with the binder Bayer Anhydritbinder AB 20 from Bayer Chemicals AG of Leverkusen, Germany.
A 55 to 60 mm thick layer of screed was laid on a separating layer of PE film. Running through the middle of the screed surface in the rooms is an underfloor duct from which electrical conduit branches out at right angles over the bare floor. Unlike anhydrite screed, cement screed is extremely susceptible to cracking in such extreme cases of duct incorporation and tends to deform in the crack zone.
According to Michael Sungen, a screed expert at Bayer Industrieprodukte GmbH, "The crystallisation of anhydrite screeds does not cause the edges to ride up. In contrast, a cement screed, where larger 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." It was thus possible to lay the screed flush with the underfloor duct at the Cologne construction site. There are no level discrepancies in the finished surface.
The use of an anhydrite screed also minimised the number of joints, reducing costs and enhancing dimensional stability. In addition, the material exhibits high strength and good drying properties.