Industrial climbers work at dizzying heights, using hot water and high pressure to remove organic growth: As part of its cultural sponsorship program, Kärcher is cleaning the Kaiser Wilhelm Monument at Porta Westfalica.
Rarely has an autumn cleanup been as spectacular as this one—both for the cleaners and for the spectators: During the cleaning work on the Kaiser Wilhelm Monument at Porta Westfalica in September and October 2019, Kärcher collaborated with six industrial climbers who rappelled down the nearly 90-meter-tall monument against the impressive backdrop of the Weser Valley. The already autumnal temperatures and the use of hot-water high-pressure washers created plumes of steam visible from afar. On clear days, the work could be seen all the way from the valley. The cleaning results are also very impressive—after all, the algae, lichens, and mosses that were removed had, in some cases, had up to 100 years to settle on the monument. This long period explains why, in addition to the algae growth—on which mosses and lichens gradually took hold—Emperor Wilhelm even found himself in the company of a small sapling. This overgrowth is not merely a visual problem—the tree that had taken root at the very top of the monument also sent its roots into the stone and joints, which can cause the stone to crack and prevent the natural stone from “breathing.”
Before climbing onto the emperor’s roof in the fall of 2019, Kärcher, together with the historic preservation office and the owner, the Westfälisch-Lippische Vermögensverwaltungsgesellschaft, is analyzing the most effective and gentle cleaning method. Test areas set up in advance will help inform the decision. The Historic Preservation Office considers the preservation of the original building fabric to be its top priority. This is because the Porta sandstone once used has become a rarity as a building stone since the 1940s: The relevant quarries have been depleted or shut down; consequently, the lighter-colored Obernkirchen sandstone was used during the restoration of the monument’s perimeter wall in 2017. The cleaning method must therefore be as non-abrasive as possible. In principle, completely manual cleaning with root brushes would also be conceivable, but due to the high labor costs, this is not economically feasible. The decision was therefore made to use high-pressure hot-water cleaning, which eliminates the need for chemicals.
The base and canopy of the monument are being cleaned by the team led by Thorsten Möwes, who, as a Kärcher expert, was responsible for overseeing the work on site, using hot-water high-pressure cleaners with a reduced surface pressure of 1 to 1.5 bar and a temperature of around 90 °C, as well as a wider-angle flat-jet nozzle set to 40 °C. This method evenly removes the biological growth and, through heat denaturation, also delays the growth of new moss. On the base, Kärcher removes lime deposits from the stone surface using low-pressure particle blasting technology and a fine aluminum silicate as the blasting agent. The deposits were formed by rainwater that seeped through the sandstone, picking up minerals that were then deposited at the exit points as the water evaporated.
Up to six professional hot-water high-pressure cleaners are in use simultaneously during the cleaning process. High-pressure hoses transport the pressurized water to the work site, where four to six climbers use high-pressure guns to dislodge and rinse away the growth. The cleaning work on the base and inside the dome of the Kaiser Wilhelm Memorial is being carried out using an aerial work platform and scaffolding.
Read more in STEIN 3/2020.
