THE RATIONALE FOR MICROABRASIVE CLEANING: A CASE STUDY FOR HISTORIC GRANITE FROM THE PENNSYLVANIA CAPITOL
J. CHRISTOPHER FREY, & TIMOTHY NOBLE
The authors gratefully acknowledge the contribution of Carl Moses, associate dean of the Lehigh University College of Arts and Sciences, whose technical and petrographic studies proved to be invaluable resources throughout the course of the study. The authors would also like to express their sincere gratitude to the following professionals who assisted with the review of this article and offered invaluable expertise and insight during its development: Kate Cowing, Katherine McDowell Frey, Mark Rabinowitz, Joseph Sembrat, and Martin Weaver.
Completion of the technical study that formed the basis for this research was made possible by the support of Merle H. Ryan, deputy secretary for public works of the Commonwealth of Pennsylvania, and Robert L. Glenn, director of the Bureau of Engineering and Architecture within the Pennsylvania Department of General Services.
1. Although considerable attention has been devoted to deterioration mechanisms for granite (Helmi 1985; Kelly 1985; Schiavon 1993; Begonhha and Braga 1996; Jones et al. 1996), a literature search conducted during the study uncovered only a few references to the use of JOS/Quintek as a means to address problematic material conditions (Zador 1992; Winkler 1994). These sources describe the JOS/Quintek process and its selection for specific programs in general terms. While certain topics involving the use of low-pressure abrasives were found (Young and Urquhart 1992), the authors were not able to locate case studies that offered comprehensive comparative information about the selection of JOS/Quintek versus other treatments.
2. The manufacturer specifically recommends a 3–5-minute dwell time, whereas this study evaluated applications that included both the recommended dwell time and dwell times up to 10 and 15 minutes. In light of the expanse of surfaces to be cleaned, the authors determined that if either cleaner were selected as the primary treatment, it would be unlikely that the contractor undertaking the work could constantly maintain a 3–5-minute dwell time in all areas. As a practical concern, it was deemed probable that even with appropriate specifications, quality standard mock-ups, and regular supervision, the treatment would dwell on some surfaces longer than the recommended dwell time at some point during construction. Therefore, the longer dwell times were examined as a component of this study to determine whether they would result in damage to the stone.
3. The application distance of 12–24 in. (30–60 cm) was deemed successful in preconstruction test panels. During construction, it became necessary to pretreat persistent, heavy crusts beneath certain overhangs with a proprietary prewash-afterwash system (SureKlean 766 Limestone and Masonry Restorer) and to reduce application distance to as little as 8 in. (20 cm). Cleaning was supervised carefully in areas where pretreatment and reduced application distances were deemed necessary.
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SOURCES OF MATERIALS AND STANDARDSFaçade Gommage
Thomann-Hanry Inc. 575 Madison Ave., 25th floor New York, N.Y. 10022 (212) 755-5550Munsell Color Services
Gretag Macbeth 617 Little Britain Rd., Suite 102 New Windsor, N.Y. 12553-6148 (800) 622-2384Quintek Rotec Vortex
Quintek Corporation P.O. Box 777 Virgil, Ontario, Canada L0S 1T0 (800) 567-0053
Note: Quintek Corporation supplies both equipment and microabrasive media manufactured by Universal Ground Cullet (M1035, M1040) and Specialty Minerals Inc. (dolomite)RILEM
RILEM 157 Rue des Blains F-92220 Bagneaux, France 33 1 45 36 1020SureKlean Restoration Cleaner, Heavy Duty Restoration Cleaner, and 766 Limestone and Masonry Restorer
PROSOCO Inc. 3741 Greenway Circle Lawrence, Kans. 66046 (800) 255-4255
J. CHRISTOPHER FREY earned a B.A. in history from Dartmouth College in 1992 and an M.S. in historic preservation from the University of Pennsylvania in 1997. He currently serves as an associate with Noble Preservation Services of Zionsville, Pennsylvania, where he focuses on the analysis and conservation of historic building materials. In addition to being listed as a professional associate with AIC in 2001, his professional and academic résumé includes experience with Historic Charleston Foundation (1996), University of Pennsylvania Field Conservation Program with the National Park Service (1996), the Frank Lloyd Wright Building Conservancy (1996), Fairmount Park Historic Preservation Trust (1995–97), and the Museum of New Hampshire History (1994–95). Address: Noble Preservation Services, 10 Log House Rd., Zionsville, Pa. 18092
TIMOTHY NOBLE received a B.A. from Pennsylvania State University in 1974 and earned an M.S. in historic preservation from the University of Pennsylvania in 1983. He is listed as a professional associate with AIC. Having served as president of Noble Preservation Services since 1992, he manages and supervises projects relating to architectural conservation and the analysis of historic building materials. Prior to establishing his own private practice, he was principal and president of Clio Group Inc. (1983–92) and director of Stenton (historic site, 1991–92). Address as for Frey.