THE RATIONALE FOR MICROABRASIVE CLEANING: A CASE STUDY FOR HISTORIC GRANITE FROM THE PENNSYLVANIA CAPITOL
J. CHRISTOPHER FREY, & TIMOTHY NOBLE
7 ADDITIONAL CONCERNS AND RECOMMENDATIONS FOR FUTURE TESTING
Having borne witness to unforeseen, long-term problems that have resulted from inappropriate treatments for historic masonry, including sandblasting and aggressive acidic treatments, the authors deemed it important to carefully test and evaluate selected practical potential cleaning treatments. This experimental program presents a methodology for preconstruction testing and offers an initial assessment of the results attained by using the JOS/Quintek System on this particular stone. Research using SEM, PLM, and so on suggested no potential negative effect on the long-term performance of the stone and concluded that this treatment effectively cleaned the stone and reestablished several potentially valuable attributes that will aid in long-term conservation. Accordingly, results from this testing program prompted the recommendation of the JOS/Quintek System as the primary cleaning procedure and formed the basis for specifications that guided work completed on the building from 1998 to 2000. While this study has incorporated a substantial amount of analytical testing, future studies could expand upon the effects of such treatments on different stone types, minute changes to surface roughness, and properties such as vapor transmission values.
Cleaning uncovered some surface conditions that were previously obscured by soiling, such as metallic and other staining. Some stains appeared on the surface several days after treatment rather than immediately afterward. This time lapse serves to reinforce the notion that final evaluation of test panels should be conducted only after an appropriate period (Boyer 1986). While a minimum of 10–14 days between treatment and evaluation was employed for this study, more extended evaluation periods are advisable to provide for the examination of treated surfaces in the presence of natural weathering.
The authors supervised the execution of all cleaning work on this building. Constant evaluation and adjustment to localized conditions were found to be essential components of the project and were particularly deemed necessary in light of the fact that the JOS/Quintek System was an emerging technology at the time of study, and studies assessing this technology were not widely available. While this cleaning system was determined to offer a materially appropriate solution, it is important to note that the containment, recapture, and disposal of several tons of media had to be considered in a construction project of this magnitude and therefore be among the criteria weighed in the final selection of the treatment. Ultimately, media containment and disposal issues were resolved with a combination of scaffold enclosures and collection at the base of wall surfaces.
As this technology gains wider acceptance and more contractors and individuals become certified to perform the treatment, the risk of the technology's being misused or misunderstood increases. It is important to recognize the lessons afforded by previous building treatments and understand that cleaning a particular surface may result in long-term negative consequences if the treatment is applied improperly or the effect of the treatment is not fully understood. While this treatment was deemed appropriate for the stone and the conditions that are the subject of this study, it may or may not be appropriate for other masonry materials or for projects where qualified supervision cannot be provided. It is simply not sufficient to visually assess a surface as being “clean” and then declare it to be materially appropriate. Testing, assessment, specification, and execution are all greatly enhanced by the input of a qualified architectural conservator who is familiar with the nature and limitations of the treatment as well as the surface that is to be treated.