Built heritage in the United States is composed of a rich diversity of materials. However, many of the country’s most prestigious and iconic structures incorporate stone as a prominent building material. While renowned for its permanence and durability, stone is not immune to deterioration. Some varieties are known to be inherently susceptible to decay. Other stones, known to be durable, may fail due to natural variations inherent in the material. Deterioration can be further exacerbated by inappropriate treatments, repairs, or other human-related factors. While the Secretary of Interior’s Standards for the Treatment of Historic Properties advocate for the retention and repair of original historic materials where possible, it is sometimes necessary and acceptable to selectively replace deteriorated stone to ensure structural stability and preserve built heritage for future generations.
The Secretary’s Standards promote the replacement, when unavoidable, of historic materials with in-kind materials. Indeed, within the field of stone conservation, it is considered a "best practice" to use replacement stone which matches the original in its mineral composition, density, and porosity. Failure to do so could hasten deterioration of the original materials in situ. Furthermore, incompatible replacements are prone to weather and take on a different appearance in juxtaposition to adjacent original materials, altering the historic character of a building.
Though in-kind replacement may be preferred, it is not often possible. Many of the original quarries have closed or are no longer producing dimension stone. Further, detailed information on the type of stone used in a building’s construction may not be available. These factors make locating suitable replacement stone difficult. When an appropriate match cannot be found, specifiers must substitute an inappropriate stone or choose a plastic repair.
In order to facilitate better matching of replacement stone for conservation purposes, knowledge of currently available sources is critical. Typically, this knowledge is dependent upon the experience of the craftspeople, architects, engineers, or conservators engaged in a particular project. There are limited resources available to assist them in making a selection. However, these resources are scattered across the internet, trade publications, and other media and are not specifically designed to provide researchers with the information necessary for stone matching purposes.
Efforts are underway in several countries to create publically accessible, detailed inventories of building stone sources to aid in stone matching. These inventories commonly include color photographs to help users identify the color and texture of stone types, data regarding their physical composition and petrology, as well as information about current availability necessary for sourcing replacements.
This project aims to build on the precedent established in other countries with the development of a National Building Stone Database for the United States. Making this information available may help improve the quality of repair work and ensure the preservation of culturally significant buildings and monuments. The project may also help identify gaps in the supply of stone suitable to match historic varieties. The benefits of such a database are not limited to the historic preservation industry. Information about available building stone is of interest to the new construction industry and will generally help promote domestic building stone products. Possible end-users include architects/designers/specifiers, conservators, contractors, geologists, and students.
The need for an inventory and publically accessible catalog of building stones for conservation purposes has long been established, as noted in the recommendations of a 1982 report by the National Research Council's Committee on Conservation of Historic Stone Buildings and Monuments.1 A 2010 publication from the Getty Conservation Center states, "Clearly, to improve on the current situation, each country with significant heritage in stone should have a centralized lithological library, and an associated database, that includes not only the petrographic and mineralogical characteristics of its stone but also petrophysical ones, including pore size distribution, porosity, capillary uptake coefficient, and hydric and hygric dilatation."2
Goals and Objectives
Catalog currently exploited deposits of dimension stone. The primary purpose of the project is to connect end users to currently available sources of stone. All stone types used in building construction and monuments, including those used purely for decorative purposes, are to be cataloged.
Provide technical documentation of stone characteristics for matching purposes. One aspect of this project that sets it apart from existing resources is that it aims to provide users with the highest, most detailed level of data possible. In addition to macro and micro scale photographs, the database will include physical test measurements, color observations, and descriptions of the mineralogical characteristics of each specimen.
Aggregate data from existing resources. While certain elements of the target data set already exist, one goal of this project will be to aggregate this information in one place to aid research efforts.
Provide free access to data. This project will result in an online database that is available to the public, free of charge. In addition, the entire database and individual records from the database will be made available to researchers to download in a machine-readable format, complying with the Federal government's Open Data Policy.
The nature of this project is intentionally limited in scope to make what would otherwise be an immense undertaking manageable. These limitations should not, however, be considered exclusive. Rather, the project will essentially be open-ended, allowing for continual expansion. The following list suggests a few areas for consideration:
Extend to historical or disused quarries. While it is not the immediate aims of this project to document historic building stone resources, the database could be expanded in the future to capture historical or disused quarries that once produced building stone.
Document prominent built examples. Examples of building stone from the built environment can help researchers better understand the behavior of particular stones over time (especially their deterioration under exposure to weathering). A number of resources including historical sources, geologists' city guide books, building records, and historic structure reports may be used to document the origins of stone building materials. Monuments, funerary or otherwise, could also be documented as a source of information.
Expand to include foreign stones. Many examples of culturally significant structures incorporating non-indigenous stone exist in the United States. In cases where a particular domestic stone is no longer available, stone from foreign quarries might provide a suitable match. The database could be expanded to include information about materials extracted from foreign quarries.
Suggest matches for unavailable stone. When a particular stone is no longer available, the database could provide additional utility in listing possible appropriate replacements. This information could be based on successful matches known from specific projects. Care must be taken, however, to caution users against relying solely on such information without conducting their own analysis.
- 1. National Research Council, Conservation of Historic Stone Buildings and Monuments (Washington, DC: The National Academies Press, 1982), p. 3. Available online at http://www.nap.edu/catalog/514/conservation-of-historic-stone-buildings-and-monuments
- 2. Eric Doehne and Clifford A. Price, Stone Conservation: An Overview of Current Research, 2nd ed. (Los Angeles: Getty Publications, 2010) p. 64.