Renovation of the Weyermannshaus Open Air Swimming Pool in Bern

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Success Stories
Watertight welding of plastic membranes is one of many Leister competencies in underground engineering. In the late summer of 2021, VARIMAT and Co in Bern began the renovation of the Weyermannshaus open air swimming pool. Swimmers are set to return to their “Weyerli” from May 14, 2022.

Authors: Silvan Horand, Product Manager and Silke Landtwing, Corporate Communication Manager, Leister Switzerland

“Weyerli” Recreation Area

The Weyermannshaus open air pool to the west of the Swiss capital of Bern, together with an indoor pool, an ice rink and park area, forms an important recreational area for the people of Bern. Locals affectionately refer to the facility as “Weyerli.”

Switzerland’s largest open air swimming pool

Anyone who employs the nationally popular infantilization technique of adding a diminutive ‘li’ to the Swiss word for a normal swimming pool is on a hiding to nothing. With a surface area of around 16,000 square meters / 172,223 square feet, the Weyermannshaus open air pool is the largest in Switzerland. With a volume of 25,000 cubic meters / 264,172 liquid gallons, it is also the largest in Western Europe. To help you imagine this: 16,000 square meters / 172,223 square feet is larger than two football fields.

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Since November 2020, however, there has been a low tide in the outdoor swimming pool, as it is being refurbished. Reason for this: The swimming pool was built in 1958 and its floor, paved with stones, had leaked over the years. One third of the chlorine-containing water seeped into the soil and entered surrounding waters. An unsustainable condition that forced those responsible to act.

November 2020 – Start of renovation work

A swimming pool renovation on this scale is a challenge for all companies and public institutions involved and something out of the ordinary. The renovation followed a tight schedule because it was originally planned to reopen the open-air pool at the start of the season in May 2022.

On September 27, 2020, the building loan of 48 million Swiss francs (approximately 50 million US dollars) was approved by voters and the restructuring work was already underway on November 16, 2020. At the core was the installation of a new water treatment system, the complete lining of the existing swimming pool with chlorine-resistant plastic liners, including UV stabilizer, and the renovation of the admin buildings.

Extraordinary scale – extraordinary amounts of material

In order to give us a sense of the scale and material requirements for this swimming pool renovation during the site visit, the contractor sent us some comparative figures: One roll of liner (25 meters/82 feet long and 2.05 meters/6.7 feet wide) is sufficient for an area of approx. 50 square meters/538 square feet. For a swimming pool, as is more likely to be found in a private environment, two to three rolls are needed for this liner. For an Olympic swimming pool (50 meters/164 feet long, 25 meters/82 feet wide, which is equivalent to an area of 1,250 square meters/13,455 square feet), approximately 15 rolls are required. The company responsible for the sealing ordered 350 rolls for the “Weyerli.” The contractor said that they probably seal such a large “pool” only once in a lifetime. The order also caused amazement from the membrane manufacturer.

Particular challenges when laying plastic membranes

The joint seam of the longitudinal and butt joints had to be continuous throughout the entire pool. To achieve this, the liners were first tensioned and then attached. This procedure prevents wave formation. The plastic membranes on the floor were then welded with the Leister VARIMAT and VARIMAT V2 overlap welding machines. Both automatic welders are designed for welding large surfaces.
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The experts amongst you may have noticed it in the picture. And no, your eyes did not deceive you: A VARIMAT from the 1990s was also used when welding the liner for the “Weyerli.” Again, proof of how durable and reliable Leister automatic welders are.

Manual welding with TRIAC and LABOR with MINOR

In addition to laying the floor, this project also involved demanding and time-consuming manual welding work. Connections, areas with high inclines and details such as corners and edges were welded by hand. Therefore, the installers used the standard TRIAC heat guns alongside LABOR handheld devices with MINOR air blowers.

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The combination of LABOR and MINOR has the advantage of the LABOR being particularly handy and light due to the external air supply. It therefore ensures fatigue-free work over a longer period of time. And that’s definitely crucial in a project of this scale. Imagine: The pool head with all its steps to get in and out is over 580 meters/1,902 feet long. This detailed work alone took about two months.

After a total of seven months of welding, the entire swimming pool was sealed. During this time, the installers worked virtually six days a week. Zoran Antic, a Tecton AG employee: “We had to take advantage of every period of good weather from A to Z, even if it fell on a Saturday.” The effort was worth it. For when the fall weather set in, the daily output fell to roughly a third of a summer day’s work. This was due to cooler temperatures, rain, dew, falling leaves and darkness. This increased the preparation effort and made working conditions more difficult overall.

Opening May 14, 2022 – on time for season launch

Good news for all water rats: It is now confirmed that renovation work will be carried out according to plan and that the “Weyerli” will reopen on May 14, 2022. A satisfied Silvan Horand, Product Manager at Leister Technologies AG: “The next time I visit our Sales and Service partner F. Jannone AG, I’ll take my swimsuit with me, because they are only 6 kilometers/3.7 miles from the ‘Weyerli’.”