MOUNT RUSHMORE, S.D., July 8 (UPI) -- A German cleaning equipment manufacturer has begun washing the lichen and grime off Mount Rushmore in South Dakota.
Thorsten Mowes, a specialist with Alfred Karcher & Co., has to combine the cleaning technique with rock climbing.
The U.S. government has wanted to cleanse the mountain sculptures without hurting the rock, but none of the cleansing techniques passed muster with officials, reported Rapid City (S.D.) Journal Friday.
The dark-gray lichens could cause the monument to discolor. The lichens' tiny roots embed in the rock, which allows freezing and thawing water to penetrate the surface, causing the rock to chip, government officials said.
The cleaning process Karcher uses involves a high-powered machine that heats water to near boiling, then blasts it onto the rock surface through the nozzle of a high-pressure sprayer, said company spokesman Frank Schad.
The hot water kills the algae and lichens and the pressure sprayer washes them and other grime away.
