Sandstone and Cement: an attractive combination


When natural stone and cement come together, they can often form an interesting contrast. Especially impressive is that of the facades of an exclusive new residential complex close to the lake of Zurich in Switzerland.
The studio of the famous architect Max Dudler (Zurich, Berlin, Frankfurt) has designed a residential complex located on a hill over the Zurich lake. It consists of 12 semi-detached housing units with a surface area of up to 260 sqm and gardens of 200 sqm and has 8 shopping outlets.
730 tons of stone for the façade
The structure of the support of the houses consists of a group in the form of grating of prefabricated elements of cement and masonry. The sections of cement are of maximum 4.9 m length, 60 cm width and 15 cm height, the masonry is 17.5 cm thick. In some of the rectangular openings of the rectangular structure huge windows of glass and others were inserted till they reached 2500 sqm, they were filled with masonry in sandstone Rorschah.
The Swiss company stone producer Barlocher Steinbruch und Steinhaurei AG ( supplied 730 tons of stone in length between 30 and 70 cm, in 5 widths ( 4,8,12,16 and 20 cm) and with a width of approximately 11 cm. The finish applied to the sandstone was mostly flamed.
Like dry masonry
The preparation work of the masonry, done in the so called Scottish Association (Schottischen Verband) , lasted 10 months. Between 8 and 10 stonemasons and laborers worked on it. Each piece had to be selected carefully, worked on and fitted with the structure in a very precise and most aesthetical manner possible. The touching and horizontal joints are between 2mm and 5mm.
On the exterior part, the joints open, giving the impression of a dry stone wall, though in reality, for the sake of stability, the pieces are joined with a special glue (PCI grey Carrament).
Sandstone Rorschach
The sandstone of Rorschah is a fine grained grey material, very homogenous with a light green shade. It is adequate for almost all interior and exterior applications. In the quarry of the company Baerlocher in Staad in Rorschach in Lake Constanza, every year around 10000 cubic metres of this sandstone are extracted using the latest diamond wire technology.
 “This work requires a trained eye”.
What was the biggest challenge for the elaboration of this work?
Owner and architect demanded an exceptionally precise execution. For example, the stones should not stand out too much, therefore, the sizes had to be sharpened to the limit. This was difficult, especially in the area of the window posts. The technical skills of the quarries and, above all, a “trained eye” was absolutely necessary for the optimum realization of the project.
Would it have been possible to do a wall of dry stone, i.e., without glues and without anchors?
Basically yes, but to insure the construction against earthquake movements one would have had to increase the thickness of the stone walls.
The sandstone Rorschah that is seen in this project is only of grey colour, but it also sometimes has yellow tones. Why have only the grey tones be used here?
The architect wanted it this way. The stones were selected with this criteria in the factory and 10 to 15 % were rejected due to this reason.
When it rains, do the surfaces of the walls show humidity in some parts?
The water flows down from the parapet over the masonry, but it is only superficial. The joints are sufficiently big to allow for the water being drained. As soon as the sun rises, the stone dries in less than half an hour. Even in winter the humidity is not a problem. The sandstone Rorschach and the adhesive used are frost proof.
Project: Überbauung complex, Zurich
Constructor: Baugesellschaft Gießen c/o Beat Odinga AG, Uster
Architect: Max Dudler, Zürich
Construction Management: Schwendener Baumanagement, Zürich
Prefabricated concrete elements: Sulser AG, Betonvorfabrikation / Baustoffe Schollberg AG, Trübbach
Stone supplier: Bärlocher Steinbruch und Steinhauerei AG, Buchen-Staad SG
Elaboration of the stone façade - companies that participated:
• Abraxas Natursteine AG, Uerzlikon ZH
• Bärlocher Steinbruch und Steinhauerei AG, Buchen-Staad SG;
• J.&A. Kuster Steinbrüche AG Bäch, Freienbach SZ
Supply of adhesives for Stone: PCI Carrament: PCI Bauprodukte, Zürich
Supply of anchors: Halfen Swiss AG, Wallisellen