Track 2: Materials over Time: Points of Change
Conservation of Charles Follen McKim’s unique façade design at Pierpont Morgan’s Library
Tuesday, September 25
10:30 AM - 12:00 PM
Location: BNCC- 101BG
The Morgan Library and Museum is a complex of buildings in New York City, one of which is Pierpont Morgan’s original library designed by Charles McKim of McKim, Mead, and White. The 1906 McKim building, as it’s now known, is poised to undergo a comprehensive restoration of the exterior, and ICR is conducting a program of extensive research, investigation, field survey, and testing to develop the treatment plan.
This presentation will focus on the original use of thin sheet lead in lieu of mortar placed at the joints between the stone courses, survey of existing conditions, the inquiry into repair options, and the challenges that these lead joints present in developing a holistic conservation approach for the McKim building.
Built of Tennessee Pink, a thick-bedded crystalline limestone, the McKim Building is a magnificent example of Italian Renaissance-style, and no expense was spared in bringing the grand design to life. As a young man, McKim visited the Acropolis and was deeply moved by the elegance of the tight spaces between the dry laid stone units. Years later, McKim had the opportunity to present this idea to his client Morgan, who agreed and one of the most unique construction techniques in the United States commenced.
Sheet lead approximately 1/64“ thick was added to the external edge of the horizontal beds of each stone block. This building technique’s success relied on the precision and quality embedded in the design specifications for both the stone selection and the carving process, which was done locally.
While lead was not a new or innovative material at the time of this building’s construction in the early 1900s, its use in this context nearly unprecedented. Lead, used as a narrow joint material, has a significantly longer service life than mortar—yet a mortar joint can be easily raked and repointed when necessary. By contrast, the lead sheet presents greater challenges, since the large stone blocks are bearing on the lead and on one another.
Existing conditions at the lead joints consist of open joints (full loss of lead), heavily deteriorated lead, previous interventions, and staining of adjacent stone. ICR conducted comprehensive surveys to better understand the extent of these conditions present.
We believe staining to be a result of the lead weathering and its primary composition of lead carbonate and lead sulfate, which are generally insoluble compounds. This compelled targeted stain removal testing, in addition to general cleaning tests for the full stone façade.
We have begun in-situ repair trials with the aim of exploring repair techniques: for example, inserting new lead into some of the weathered or open joints where water infiltration is a concern. This presentation will evaluate the efficacy of these trials.
- Describe the development of McKim’s design goals for the façade of the Morgan Library and how critical Morgan’s acceptance of McKim’s vision was to the success of the building.
- Demonstrate familiarity with the architectural conservator’s approach of conducting surveys, testing, and developing treatment options with which to move the goals of a project forward.
- Describe the masonry construction techniques that were utilized to create the incredibly thin joints of the McKim building and how these techniques were adapted from traditional dry laid masonry.
- Realize the intricacies and challenges of introducing repair materials into historic building facades, in addition to potentially changing the environmental behavior of that building system with the restorative intervention.