“The Evolution of Mortar”: A Presentation to Stone Mason Interns at Historic Eastern State Penitentiary Museum
My CSP colleague John Biehl and I recently spoke on the evolution of mortar for a group of stone mason interns at Eastern State Penitentiary Historic Site in Philadelphia, which was in operation from 1829 until 1971. The prison was abandoned for 20 years and is now a major preservation project. After our introduction, we conducted a hands-on Jahn training in stone repair.
Stonecutting interns gather for a CSP demonstration at Eastern State Penitentiary Museum.
I enjoy training young masons and stonecutters. It gives me a chance to get back to the basics of what we do—those key factors that, when done properly, result in a long-lasting patch.
Demonstrating the all-important “peanut butter coat”
We had the chance to demonstrate the “peanut butter coat” in person, demonstrating how to make sure the stone is fully saturated and then applying a thick enough coat, which is of utmost importance. This process helps create a permanent bond between the patching mortar and the substrate.
The interns learned why it matters that Jahn material does not contain bonding agents, latex, or polymers. The omission of such additives allows water and salts to pass through the patches without any interference or pressure buildup. Maintaining permeability is what allows these patches to perform at a high level for so many years.
We talked about the importance of compatibility–and how Jahn Mortars are specifically engineered per substrate. To maintain compatibility, Cathedral Stone tests for compression, bending tensile, expansion/contraction, permeability, and salt handling. We explained the long-term effects of repointing with materials such as lime and grey Portland on historic stone.
A cell block at Eastern State Penitentiary
The interns, who are just entering the stonecutting profession, were interested to hear why training and certification are so important for installers of Jahn mortars.
You can imagine why Eastern State was an interesting setting for this demonstration. It’s a massive granite and fieldstone structure. As you walk around the premises, you can really feel the history. The prison was the model for 300 others worldwide, and the design has a religious inspiration. It has a five-spoke radial floor plan of cell blocks that creates the feel of a church. Low doorways forced prisoners to bow before entering, and a single skylight in each cell suggested the “eye of God” was watching.
I found it fascinating, and it was great to talk about my interests and career with these interns, who had just completed their first historic preservation project. I’ve advised on techniques and methodologies and consulted with architects on some of the most prominent buildings in the northeast. Independence Hall. The Empire State Building. Ellis Island. I feel very fortunate to be a part of a team that helps restore and preserve these historic structures.
