Masonry Magazine September 2005 Page. 27
Decade after decade,
the copper-impregnated
water ran off the
bronze and soaked into
the stone.
Orange Stains at St. Andrew's Cathedral
ABOUT 30 YEARS AGO, workers installed metal grates on the windows of St. Andrews Cathedral in Grand Rapids, Mich. During recent restoration work, conservators discovered the stains. Three decades of water running off the metal onto the historic brick - a buff yellow from the 1800s - left deeply embedded orange stains in the wall around the windows.
Doug Barron, an industry consultant with Seals Inc., in Bridgeport, successfully tested a specialty liquid cleaner for metallic staining on the rusty brick. The cleaner, Sure Klean Ferrous Stain Remover, works by re-dissolving the iron oxides that caused the stain so that they can be flushed away with a fresh-water rinse.
"We got the stains out 80 to 85%," Barron recalls. "The clients were very happy. They didn't want their historic building to look totally new anyway."
Green Stains on Wacker Drive
DURING THE RECONSTRUCTION of Chicago's Wacker Drive in 2003 and 2004, workers faced deep, penetrating copper staining on porous Indiana limestone.
"They were bright green streaks, almost kelly green on the gray stone," says Jim Lucas, a consultant and masonry expert with Lucas & Associates in Hammond, Ind. "They varied in length from a few inches to six feet."
The stains occurred on the south side of the split-level thoroughfare, where bridges spanning the Chicago River met the drive. Since 1924, rain, sleet, snow and ice washed over bronze commemorative plaques, planters and light fixtures. Decade after decade, the copper-impregnated water ran off the bronze and soaked into the stone.
Removing the deep stains required a poultice cleaner, Lucas explains. Workers used a proprietary poultice specifically designed for copper staining.
Poultice cleaners go on stained substrates in paste form. In this case, workers created the paste by mixing a powerful cleaning agent packaged together with a compatible clay powder. They covered the paste with plastic and fastened it down with duct tape. As the poultice dried overnight, it pulled the contaminants out of the substrate. When the dried poultice was removed, it also removed contaminants from the masonry pores.
Lucas reports that by using the poultice method, workers removed about 95 to 98% of the green metallic staining from the limestone.
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September 2005
Masonry 25