Reference

Zürich Mülligen Sorting Office

The sorting office in Zürich Mülligen is the largest sorting office in Switzerland. The building was constructed in 1985 by the well-known architect Theo Hotz and converted into a mail distribution center in 2008. For the past 15 years this building, over 300 meters high, has been under a cultural heritage preservation order of the Canton of Zurich. Every day, several million letters are sorted on 14-kilometer conveyor tracks.

The building, with a façade area of 36,000 square meters, is enveloped in rainscreen cladding in a sandwich structure. When it was built, the aluminium façade was one of the first in Switzerland to have a powder coating.

The distinctive façade was showing signs of wear and tear. Analyses and inspections revealed that it was still doing its job and that no urgent renovation work was required. However, the grey color (NCS S 3502-B) was very weathered, with considerable chalking and loss of shine.

The façade no longer reflected the significance of the building, and the Swiss Post decided on renovation. Since its authenticity could not be lost, the façade renovation concept had to be developed in conjunction with the Cultural Heritage Preservation Office for the Canton of Zurich.

The Swiss Post did not leave anything to chance. As early as 2014, various different products were applied to sample areas on the south-west façade and observed for a trial period of one year. It was important to the planners that the coating system met the Qualicoat class 3 specifications and that there was evidence of its lifespan, whether with the Florida test or other checks.

In 2015 the contractors and façade planners inspected several buildings in the Greater Zurich Area which were protected with fluoropolymer systems. During these visits, they also saw the Bank of Julius Bär in Zürich-Altstetten, renovated in 2011, and the Pfingstweidbrücke (bridge) in Zürich-West, newly built in 2010.

Because of weather conditions, the renovation could only be carried out from springtime to autumn. Due to the large area involved, renovation took almost three years (2016 to 2018). The work had to be arranged so that the logistics of the business with a great many deliveries and shipments by lorry and rail could proceed unhindered.

Pre-treatment

The first step was abrasive cleaning of the surface so that the dirt particles embedded in the top layer of the existing coating could be removed. The surface was cleaned with a high pressure system, followed by Qualiprotec Cleaner N. Cleaner N, with Scotch Brite incorporated, is a neutral cleaner which softens the dirt particles. After the cleaning operation, the surface was dry sanded, cleared of dust, and finally rinsed.

Primer

The primer is used to reinforce and seal the substrate so that no dirt particles can penetrate the new top coat. A spray application of 1 x 40 – 50 µm Qualiprotec Korrgrund Q220, a matt epoxy primer with active corrosion protection pigments, was carried out, and a light grey color (NCS S 2502-G) was selected.

Top Coat

When the contract was awarded, the color of the top coat had not yet been determined.  Various grey tones were applied to the façade and the Cultural Heritage Preservation Office specified a satin gloss NCS S 3502-B as the definite color.

The fluoropolymer Qualiprotec Re-Vitaliser Q131 paint was used. In places where the surfaces could be encased, the top coat was sprayed at 30 to 40 µm; in the non-encased areas the paint was applied by roller.

Quantities used

  • Qualiprotec Cleaner N: 1’500 l
  • Qualiprotec Korrgrund Q220: 8’500 kg
  • Qualiprotec Re-Vitaliser Q131: 7’000 kg

Competences in this project

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Urban Weber:
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