Bikini-Haus Berlin, Germany

Bikini-Haus renovation: Structural and fire safety problems solved by a lightweight screed from SCHOMBURG

In the centre of the Charlottenburg district of Berlin, next to the zoological gardens, there stands an old listed commercial and office building – the well-known Bikini-Haus. It now gleams with a new brilliance. When renovating the floors, there were particular structural and fire safety requirements. With the help of the lightweight screed, ASODUR-LE (Bindemittel) from SCHOMBURG, these were able to be fulfilled.

In the period between 1955 and 1957, the stretched low-rise building with 6 floors was constructed following the plans of Architects Paul Schwebes and Hans Schoszberg. On the ground floor of the building there are rows of shops beneath an open portico. At the time of construction, the middle storey was conceived as an open access balcony and consequently gave the building a two-piece structure,like a bikini, from which the name of this venerable house originates. Four staircases are located at the rear.

During the last 50 years, the house has been in constant change, nevertheless whilst retaining its fundamental style. Even the typical large undivided bank of windows with their minimalistic profile, have remained and this was to be maintained after the alterations. The use of the new Bikini-Haus was, however to radically change. What formally occasionally served as a theatre and an office building was now to be converted to a hotel and shopping complex.

As owner, Bayerische Hausbau started the conversion in December 2010. Following the design of the Belgian Arne Quinze and his Architectural practice SAQ, the bikini storey was to be converted to its original appearance and the adjoining roof terraces to be extended. A total useable area of 54, 000 m² was established.

During the renovation, the Bikini-Haus was gutted. As a consequence, a new floor had to be constructed. It was necessary to build a hollow floor. There was a requirement to find a material with which to level an uneven concrete substrate in such a way as to permit a hollow floor to be constructed on top. Care had to be taken to apply a material, which conformed to the strict fire safety guidelines. In addition, a screed could only be installed, whose weight did not overload the existing concrete floor and also fulfilled the high structural requirements.

Following technical advice from SCHOMBURG to the consultancy firm Hild and K from Berlin, the cement-based lightweight screed ASODUR-LE (Bindemittel) from SCHOMBURG was jointly recommended. This is classified as CT-C25-F4 in accordance with the screed standard EN 13813. Furthermore, ASODUR-LE (Bindemittel) conforms to fire protection class A1 and was therefore suitable for use in the BIKINI-Haus. With a surface weight of approx. 14 kg/m²/cm screed thickness compared with conventional cement-based screeds with a surface weight of approx. 22 kg/m²/cm screed thickness, one could reckon on a weight saving of approx. 37%.The calculations of the Structural Engineer also confirmed the plans. The advantages of the SCHOMBURG lightweight screed compared with conventional lightweight construction systems was the deciding factor.

Bozkava and Günay Estrichbau Gbr from Berlin won the contract. The experienced screed installer was able to prove their ability from many previous projects. For example, the company was responsible for the screeding at the privy council building in Berlin-Mitte, the ALEXA Shopping-Center in Berlin Mitte and the Lehrte station, part of Berlin’s central railway station. Bozkava and Günay Estrichbau Gbr could also prove their Know-how outside Berlin, in a range of areas, such as heated screeds, floating screeds, bonded screeds, industrial screeds, lightweight screeds, rapid screeds and resin coatings.

After a short briefing from one of SCHOMBURG’s technical advisors, work could begin. The sceed was to be installed bonded with ASOCRET-HB-Flex serving as the bonding slurry. Following a thorough clean of the concrete substrate, this was adequately pre-wetted. Now the bonding slurry could be applied with a conventional broom. The screed was then installed wet in wet. For mixing, the employees of Bozkava and Günay Estrichbau Gbr used a Screed Boy. The experienced screed layers achieved 200 m² - 300 m² per day. A total of approx. 4,400 m² of bonded screed were produced. Almost 200,000 kg of ASODUR-LE (Bindemittel) and over 5,000 kg ASOCRET-HB-Flex were consumed.