Unclouded marble shine – thanks to invisible fastenings

The design was created by the Zurich architectural firm Office Haratori and the architects from Office Winhov in Amsterdam. The planners succeeded in expressing the client’s field of activity through the architecture as well. The renovation of the building and the newly executed marble façade in 2017/2018 integrate the commercial building into its surroundings. Additionally, the renovated commercial building simultaneously represents durability, timelessness, innovation, and perfection—the "core business of the Bucherer company," according to the architects. While the ground floor is entirely dedicated to the material bronze, the carefully arranged marble slabs characterise the floors above. The stone comes from the only marble quarry in Switzerland, located in the canton of Ticino. "We refine the marble from Vallemaggia into precisely crafted, jewellery-like elements," says Office Haratori about the design. "The façade—similar to a sundial—reflects the passing of the day and seasons. The marble relief appears in the changing shadow patterns, sometimes softly expansive, then sharp and orderly."

The facade consists of approximately 100 different steel tube lattice structures, equipped with conically tapered marble pieces ranging from 6 to 18 cm in thickness and of various sizes. These components were prefabricated into elements at the factory. Later, they were hung on-site in blind installation on 6 to 8 pins. The individual weight was up to 4.5 tons. Precisely positioning such heavy elements with an eccentric centre of gravity so that all pins are hit was a major challenge. Especially since the steel elements were not flat but deformed by up to 10 mm, which is unavoidable in steel construction. This hurdle could only be overcome with a suspension device specially designed for these elements. The business unit fischer Fassadensysteme of the fischer Group was responsible for fastening the marble slabs to the steel structure using undercut technology. The undercut holes were drilled with a tolerance of less than 1 mm. This meant a very high effort, as Steven-Henrik Maier, Market Manager fischer Fassadensysteme, reports. “Challenges arose regarding the high loads due to the dead weight of the slabs up to 180 mm thick. To prepare the correct and safe execution, several pull-out tests were necessary.” The tests were carried out with different slab thicknesses (30, 40, 60, 80 mm), also near edges and with larger slab formats. As a result, to be able to transfer the loads, a special anchor with a higher embedment depth was designed.