Stone conservation has come long way in the modern era with extensive research into the methods of repair. Over the last fifty years, a number of routine methods overlooking the compatibility of materials or utilizing an abrasive approach have been proven harmful to the long-term stability of the stone. Damage can be avoided and the historic stone preserved, cleaned, or repaired through a thorough understanding of the material make-up of both the stone and mortar as well as the repair required. Whether stone has been discolored or damaged due to age, elements, or trauma, it is prudent to conduct a cursory analysis of the material to devise a sustainable approach to conservation.
Like any conservation analysis, a Historic Stone Analysis is carried out to determine and inform on a number of factors. The specifications uncovered during the onsite testing aid in developing the conservation program and allows the conservator to address the work fully informed on the unique status of the project. Additionally, the report informs the Owner on the time and money required for the repair thus assisting in the development of project budgets and timeline.
A Historic Stone Analysis is a combination of onsite testing, laboratory analysis if necessary, and research. The findings and research are compiled in a report with recommendations for conservation. The following points are what you may expect detailed in a report:
Description of the Material & Damage / Decay
Whether the damage is a result of the elements, poor conservation efforts, or surface trauma; understanding the underlying need for conservation in tandem with the physical make-up of the stone will drive the conservation program. Stone decay or discoloration occurs in many different forms depending on the type of stone and the location. The severity and rate of decay/discoloration will determine the extent of remedial action and the urgency. In effort to take sustainable conservation actions, identifying the cause of discoloration and decay may also encourage the building owner to take preventative measures.
Onsite Observations and Testing Results
Onsite testing utilizes a number of hands-on and observational techniques. A comprehensive understanding of the stone and its properties as well as experience working with stone will inform the observations relating to the origin of decay/discoloration/damage. Onsite testing will depend on the object being studied. Laboratory analysis may also be conducted to further study the mortar mixture and properties of the stone. Surface damage may be studied with line profilometry measuring technology and interior damage studied through ultrasonic technology to determine the presence of cracks and inconsistencies in the stone. In cases of extreme decay, consolidation may be required to reconstitute the strength. In areas of loss, replacement and color matching may be explored. Cleaning tests may be carried out to determine the most effective method. Stone may be cleaned through use of poultices, solvents, and resins. For example, a different approach will be required for an interior statue to an exterior wall: they are separate types of construction and serve different purposes.
Recommendations for Conservation
Following the guidelines from the American Institute for Conservation (AIC) to “do no harm,” recommendations should be restrained and effective. We strive to determine the least invasive and most effective solution that will ensure long term stability. Since every project is unique, recommendations will vary depending on the observations and a modified approach may be required in certain areas due to the level of stability noted. It’s critical to remember that the appearance of cleanliness does not always correlate to the stability of the stone. Determining the extent of cleaning in relationship to long term stability and aesthetic appearance should be clearly explained to manage the project expectations.
With the report from the analysis, the Owner should clearly understand the properties of the stone, the cause of the damage specific to their project, onsite testing statistics, recommendations for repair, and in cases of cleaning tests, tangible evidence. With an informed approach, the report not only guides the project but also becomes archival documentation for future reference.
