Kärcher, which last year had sales of $1.73 billion (at current exchange rates), said it did three or four philanthropic cleaning projects a year. The latest was at the Vigeland Sculpture Park in Oslo, a permanent outdoor exhibition of some 200 works of the sculptor Gustav Vigeland that is visited by about a million people a year. To mark a quarter-century of business in Norway, Kärcher selected the park’s most popular attraction, a granite monolith standing more than 42 feet high.
“There is naturally some skepticism toward people offering something for nothing, but this was a true collaboration and beneficial to us from Day 1,” said Jarle Stromodden, director of the Vigeland Museum, which is responsible for the sculptures in the park. “The monolith had been cleaned before, but this was the most thorough cleaning ever, which has very much to do with the equipment Kärcher has.”
Mr. Stromodden said the main concern of the park’s conservators had been protecting the surface of the delicate granite.
“Kärcher showed good knowledge of the material and worked with the conservators to determine how much pressure could be used without damaging the surface,” he said.
But the work at the park was simple compared with the challenges presented by the Vatican colonnade, whose white travertine marble columns, by Bernini, were black with soot and other grime.
Kärcher, which negotiated with the Vatican for two years before beginning work on the colonnade, spent nine months cleaning it, in part because the project was on hiatus during the Christmas season.
“The layer of dirt on the columns was very sturdy, oily and greasy from auto emissions,” said Frank Schad, a Kärcher executive.
The company first tested the use of water alone, initially as steam, then propelled by high pressure and even shot through a rotating nozzle, but with little success. It then began testing abrasives, ultimately settling on calcium carbonate propelled by air pressure. (“We try to avoid the word ‘sandblasting,’ ” Mr. Schad said.)
The cleaning was the most expensive of Kärcher’s monument projects to date, although the company declines to discuss the cost.
Mr. Jenner said the cleanup of the faces on Mount Rushmore, in the summer of 2005, was the project dearest to him because of its sheer scale and the natural setting.
The faces, carved from 1927 to 1941, had never before been scrubbed when Kärcher approached the National Park Service. The agency “had had a project on the books for some time anyway, and their offer provided us an opportunity to get going on it,” said Duane Bubac, chief of cultural resources and facilities for Mount Rushmore National Memorial.
The park service had known that lichen was creating pockmarks on the monument, but analysis by the University of Stuttgart also found that deposits, possibly tied to the coal industry, were gradually loosening the surface.
“The results of the study,” Mr. Bubac said, “helped us realize that other work needed to be done — fracture sealing and other repairs.”
The park service did not allow Kärcher to use any chemicals or materials foreign to the park, so soda and detergent blasting, two potential cleaners, were out of the question. Instead, hot water and a pressure washer did the job. The water had to be pumped 300 feet up the mountain to a basin and then piped to the workers doing the cleaning.
The park was open through the entire process, and some visitors made special trips to see the cleaning while it was under way.
“One of the original carvers commented that he ‘hadn’t seen that in over 60 years,’ ” Mr. Bubac said. “We asked him what, and he told us he was seeing the sparkles in the granite again.”
- Stephanie Strom, The New York Times