

Crews used a technique known as "in-painting" to effectively erase graffiti at the Barker Dam in Joshua Tree National Park/NPS Crews used a technique known as "in-painting" to effectively erase graffiti at the Barker Dam in Joshua Tree National Park/NPS

It took more than a year, but crews at Joshua Tree National Park, aided by professional conservators from the University of New Mexico, have largely "erased" graffiti scratched into the Barker Dam, a historic site inside the California park.

The year-and-a-half partnership culminated with a weeklong project from March 22- 29, where architectural conservators from the University of New Mexico volunteered their skills to effectively mitigate the visual impacts of scratched graffiti from the entire surface of the dam.

Barker Dam is listed on the National Register of Historic Places. The dam was originally constructed by the Barker and Shay cattle company in 1902 and was added to several times by William 'Bill' Keys, a homesteader and local legend. The dam serves as a tangible reminder of the tenacity and ingenuity of homesteaders struggling to survive in the extreme deserts of the American Southwest.

Rusted metal pipes scavenged from abandoned mines protrude from the top of the masonry and concrete dam that catches and holds seasonal precipitation. No springs exist in the area, so catchments such as Barker Dam were vitally important for ranchers and homesteaders trying to settle the desert.

The dam can still hold water, but the ongoing drought in California has severely reduced annual precipitation. Lowering water levels in the dam exposed the naturally weathered surface and vandals were quick to act. In less than a year, scratched graffiti spread across over 50 percent of the entire surface of the dam.

Aside from the physical damage to the concrete, which has resulted in spalling and deterioration in some places, the presence of highly visible scratched graffiti only encouraged people to add their names and messages. UNM conservators employed a method known as 'in-painting' to blend the scratched areas into the surrounding naturally weathered surface. After testing a variety of different methods ranging from dry and wet brushing, to low-pressure power-washing, and various types of paints, the conservators settled on silicate based paints for their durability and the ability to re-treat these areas in the future without having to remove the current treatment.

'In-painting' is a time-consuming and labor-intensive process that involves adding pigments to the scratched areas with a method similar to the painting style of pointillism. Instead of merely painting over the graffiti entirely, the paint is applied in a way that matches the surrounding colors, textures, and patterns. '¨The Park Service has a long history of dealing with graffiti on historic structures, rock art panels, and other irreplaceable cultural resources. The conservators from the University of New Mexico working through the CESU network have played an increasingly important role in developing the best methods and techniques based on the highest professional standards.