The Race to Save the Ruins
Old restoration practices may have done more harm than good; now scientists are scrambling to remedy the damage
By Michael Bawaya | From Preservation | January/February 2011
In the early 1920s, the National Park Service faced a considerable challenge. How could scientists and archaeologists, charged with managing and caring for the nation's priceless cultural resources, stabilize hundreds of ruins—some more than 1,000 years old? They needed a versatile material appropriate for numerous sites—something affordable that would last at least 20 or 25 years. And that's when they hit upon Portland cement. It seemed ideal, says John Schroeder, an archaeologist at Joshua Tree National Park in Southern California, because the cement was available in vast quantities and required "the least amount of cyclical maintenance."
Portland cement, the basic ingredient in mortar, stucco, even bathroom grout, became the material of choice at countless historic sites, and was used to treat irreplaceable treasures across the American Southwest. Experts thought they'd discovered a magic bullet. "They figured they wouldn't have to come back and visit these sites for years," Schroeder says.
But by the early 1980s, the Park Service realized that something was terribly wrong. Portland cement had proved so durable and so hard that it was causing the softer materials that composed many ruins (think adobe and sandstone) to erode. Just as dangerous, cement had a tendency to channel water into the ruins' sandstone and earth mortar, leading to gradual but irreversible degradation. These drawbacks only compounded concerns that the cement failed to match the original materials, thwarting the service's stated intention to make ruins under its care aesthetically pleasing.
Officials realized they had to rethink their stabilization efforts. "The wholesale approach of using cement to preserve everything was left behind in lieu of preservation practices tailored to the particular characteristics of a site," says Virginia Salazar-Halfmoon, manager of Vanishing Treasures, the National Park Service program that has supported 165 preservation and documentation projects since 1998.
Letting Them Go
Some Native Americans believe that everything, including an ancestral site, has a natural life cycle, at the end of which it should rightfully expire. Gary Brown, at Aztec Ruins National Monument, says, "The view that these sites should return to the earth through natural deterioration is sometimes expressed during formal, government-to-government consultation between the Park Service and some tribes. But most representatives understand and appreciate our mandate to preserve archaeological resources for the future and not allow them to deteriorate."
Virginia Salazar-Halfmoon, of the Vanishing Treasures program, notes that in certain cases where the ruins are inaccessible to visitors, the National Park Service does accede to requests by tribes to let ruins deteriorate.—M.B.
Today's approach is to determine the causes and effects of decay, and then remedy the conditions with less invasive procedures. "There's not a one-size-fits-all solution," Salazar-Halfmoon says.
No one knows more about the dramatic ways that the maintenance of ruins has changed than Frank Matero, a University of Pennsylvania professor of architecture and historic preservation who has consulted on projects around the world.
In 2008, Matero was called to Mesa Verde National Park, which contains more than 4,000 documented archaeological sites. (The park has received more than $3.6 million in federal and private funds from Save America's Treasures, a public-private partnership between the National Trust for Historic Preservation and the Park Service.) Though some sites date to the 10th century, Mesa Verde is primarily known for its 13th-century cliff dwellings—considered among the best preserved in North America. Matero had worked on ancestral sites throughout the park since 1994. This time he was charged with stabilizing a wall at Far View House, a mesa-top site threatened by exposure and the wild extremes of climate common to southwestern Colorado.
Focusing on an ancient wall that had been capped with Portland cement, Matero attempted an approach he had previously used in Turkey. He removed the cement and then replaced it with a new cap made from soil, plants, and synthetic materials. Matero believes it's the only time that this approach, called "soft capping," had been tried in the Southwest.
Within a year, monitors placed in the base, middle, and top of the wall showed that the soft capping was doing exactly what it was supposed to do: protect the wall from thermal exposure and reduce dangerous moisture penetration. As a result, officials at Mesa Verde began considering the use of this technique to help stabilize other ruins. "It has great promise," Matero says. "It's maintainable, it's sustainable, it's green, it's low cost, it's repairable. It's all those things, and that's what we want."
Matero's interest in new materials and approaches did not stop with soft capping. Last summer he and a crew moved to another site at Mesa Verde called Spruce Tree House, the park's third-largest cliff dwelling, which was constructed by the ancestors of the Puebloan peoples of the Southwest.
The plaster on some of Spruce Tree House's significant walls was detaching, delaminating, and blistering. But there were limits to the remedies Matero could apply: Native Americans oppose the use of unnatural substances to repair ancestral homes, so his team needed a natural substance. The scientists opted for gelatin, an adhesive derived from fish and animal parts that was commonly used for conservation in the 18th century and abandoned only after synthetic materials became widely available. Gelatin, combined with glycerine for flexibility, is "low impact, effective, and durable," Matero says. "The treatment is also nontoxic, safe to the conservators and public as well as the environment, and low cost." Today the endangered plasters at Spruce Tree House are protected and stable, the positive result of what Matero calls an "elegantly simple" repair.
At Bandelier National Monument, in northern New Mexico, a team led by Douglas Porter, a visiting professor in the school of architecture at the University of New Mexico, is also changing the face of preservation. Porter and his group recently created a 3-D model of an ancient masonry wall to determine its stability—the first time that the modeling process, currently in development at the Massachusetts Institute of Technology, has been used on ancient ruins in the United States.
The computerized modeling was part of a project to document and conserve Bandelier's cavates—hand-hewn chambers carved into volcanic stone, or "tuff." Native Americans lived in these chambers, which are unique in the architecture of the American Southwest from the 12th to the 16th centuries. There are more than a thousand in Bandelier's Frijoles Canyon, and thousands more in the surrounding areas. The entrances to the cavates now resemble a giant, exposed honeycomb, but originally they were masked by masonry walls and multistory buildings, most of which collapsed over the past 400 to 500 years.
Porter's team focused on cavate B002, which once had two enclosure walls. The surviving wall, the largest masonry enclosure left in situ in the canyon, seemed likely to collapse in the near future: Not only was it missing mortar, the tuff at its base was also eroding, and a boulder-like mass of tuff on top was only tenuously connected to the cliff wall.
Intent on accurately assessing the wall's condition, researchers scanned both the wall and part of the surrounding cliff face, then processed the data to analyze stability and possible collapse thresholds. "They simulated the modes of collapse," conservator Angelyn Bass says, and learned—to their amazement—that the seemingly fragile wall was reasonably stable, in part because the boulder pressing down upon it helped the wall to endure strong winds. Porter notes that the existing condition does not guarantee future survival: "While the wall is currently in equilibrium with the forces acting on it, changes in current conditions could alter that drastically."
Researchers are now completing additional experiments that will allow Bandelier officials to decide whether and where to take further action. Given the fragility of some ruins, treating them can do as much, if not more, harm than good. In the case of the wall, says Bandelier's chief of resources, Barbara Judy, site officials may conclude that "documentation is the treatment."
Advances in preservation have not totally replaced traditional methods, as Virginia Salazar-Halfmoon is quick to point out. "The Vanishing Treasures program is split pretty evenly between the university-trained preservation professionals and those trained in traditional building skills and trades," she says.
Frank Matero and other professionals at the Park Service agree that blending new techniques with more traditional approaches is the way of the future. "The biggest challenge is to find the right balance between remedial and preventive actions," Matero explains. "This is especially important for archaeological sites, where physical evidence is critical for interpretation now and in the future."
"We're doing the right thing," adds Gary Brown, chief of cultural resources at Aztec Ruins National Monument, in northwestern New Mexico, referring to the discontinuation of Portland cement as well as consultation with Native American tribes about preservation projects. He notes that the National Park Service now sees the wisdom of the Native Americans' admonition: "The ruins need to breathe."
Michael Bawaya is the editor of American Archaeology magazine.
Michael Bawaya is the editor of American Archaeology magazine.
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