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Materials I: “Performance-based Evaluation of Materials & Methods for Monument Conservation”

Norman R. Weiss and Irving Slavid

This paper discusses laboratory and field studies undertaken by the authors to determine and/or predict the effectiveness of a range of stone conservation treatments used in historic cemeteries. The techniques utilized to evaluate treatment efficacy range from laboratory instrumentation to inexpensive, low-tech procedures (such as tape testing) that are suited to being performed on site.

The choice of particular materials and methods involves a surprising variety of parameters, including ease of use, which is often related to the conservator’s level of skill. Manufacturers’ recommendations and product cost also play significant roles in the selection process. In most situations, the decision to accept a treatment (and to use it extensively) is only based on an initial sense of success, related to appearance upon completion of the remedial work, or to short-term behavior without obvious failure.

When systematic testing is done prior to product selection, another problem is encountered: the lack of deteriorated stone from which to produce specimens for comparative laboratory assessment. The authors will discuss the use of small specimens (derived from weathered building materials) in their work, presenting information on breaking strength and ultrasound measurement.

Ultimately, however, the key issue is that of performance, that is, long-term behavior in service. Most experts agree that the best approach to studying performance is periodic inspection. Cemeteries, essentially arrays of stone outdoors, lend themselves to this concept, if stone conservation efforts are thoroughly and systematically documented, and if we come together as a community to share information on product performance.

But even experienced practitioners seldom return to re-examine their work years later, nor do most of us have the patience to wait for such long periods of time to fine-tune our conservator’s bag of tricks. Accelerated weathering tests (such as freeze/thaw and acid rain simulation) will be reviewed in this presentation, and compared with observations made on technical aspects of the authors’ fieldwork over the past decade.

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