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.
“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.
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.
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.
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’.”