In Part 1, we learned how a plaster on wood lath ceiling is made, how it functions as a loosely suspended system and how it deteriorates systematically over time. In Part Two, we find out how a residential contractor in Canada took an idea from the pioneer of architectural conservation and turned it into a state-of-the-art treatment method called plaster consolidation.

By understanding how a plaster ceiling functions as a system, Rod Stewart was able to figure out how and why it systematically deteriorates:

“Okay, you’ve got a 10,000 square-foot plaster ceiling that’s being held up by thousands of beautifully formed keys and lugs. What happens if one of these keys and lug deteriorates and breaks? The answer is simple: the support work it was performing is passed onto the adjacent keys on either side. This represents a 50 percent increase in the load they are taking up. If the next key breaks, the load on its neighbor increases to 150 percent. As more keys break, the load on other keys increases exponentially and the deterioration is hastened. The situation can—and will—only get worse. While it is true that some areas of the ceiling are in better condition than others, it is certain that all areas of the ceiling have deteriorated to some extent and that this process of deterioration is unrelenting. And as they deteriorate they become more and more fragile.”

“Apprehended Collapse”

Stewart believes there is a pressing need for a comprehensive or holistic approach to the repair and restoration of historic buildings erected in North America, mostly during the 1800’s. He points out that many of these buildings are now in the midst of complete dismantling and renewal programs, almost entirely because they were constructed with premeditated haste. Referencing the writings of architectural historian and critic Herbert Muschamp, Stewart notes that the buildings in which he specializes were the products of the social history of the 19th century, when governmental and religious authorities sought to quell revolutionary fever and establish dominance and order over an unruly population.  Cathedrals, churches and government buildings were swiftly erected to create imperious and majestic barns that were designed for awe-inspiring intimidation but not for longevity. One hundred and fifty years later, this New World approach—radically different from the European tradition of brick, stone and mortar that could see decades, even centuries pass before the completion of a structure—has resulted in buildings that are, from top to bottom, in immediate need of rehabilitation. Stewart compares them to aging stage sets: temporary, flimsy and well past their maintenance-free service life. “Piecemeal repairs do not address the endemic problem of overall deterioration,” he states. “The plaster requires a systematic treatment that is consistent with the program being applied to the rest of the building—a holistic approach.”

Stewart is quick to point out that while the Phillips’ method of reattaching plaster does not constitute a holistic way of conserving plaster, it was by no means a failure.  “The idea of using acrylic adhesives was itself a major breakthrough. It was actually brilliant in many respects, but it offered only an interim repair at isolated spots on the ceiling. My goal was to find a method that would offer a systematic and lasting repair of the entire ceiling. When the mechanical suspension system has failed and where loss of the ceiling is imminent, plaster should not be a sacrificial component in the way that mortar is a sacrificial component of a masonry wall.”

Stewart’s point is that a 150-year-old plaster ceiling has been experiencing gradual deterioration—often accelerated by outside forces—from the day it was built. While failure of the ceiling may not be imminent, it is unquestionably inevitable.  It is in a state that Stewart calls “apprehended collapse.”

At this point, Stewart philosophically parted ways with Phillips. “Phillips treatment method basically made points of contact between the plaster and the wood lath and then strengthened those points of contact with an acrylic adhesive. He found a way to get the acrylic delivered to spots on the ceiling that he thought were most vulnerable and he made connections at those locations. So it’s very much like a ‘chemical nail’ or a ‘chemical screw’:  he’d drill a hole from the top side of the wood lath to the surface of the backside of the plaster and introduce an acrylic adhesive to that location. And because he used a thickened or filled adhesive, he was able to pile up that material so that it came back up through the space and connected to the wood lath. It was indeed like a ‘chemical nail’.”

Stewart’s essential problem with Phillips’ method was that while these “chemical nails” did succeed in connecting different parts of the ceiling to the wood lath, it was only a matter of time until another set of chemical nails would be needed because the overall systemic problem of unrelenting plaster deterioration had not been addressed.

Those who know Stewart will attest to the fact that when he starts thinking about something, remarkable things tend to happen. Neal Mednick, a colleague and friend of Stewart for more than 35 years, said, “He has a feverishly inquisitive and imaginative brain that is unfettered by the constraints of a formal education. He always thinks outside the box. His brilliance lies in his ability to look at a problem and come up with a simple, sensible solution that, for some reason, no one else has thought of.”

Unsatisfied with the Phillips method, Stewart focused his attention on finding a variation that would address a plaster ceiling as an entire system. He began experimenting with the concept of “flooding” the ceiling from above with acrylic resins, selected for their flexibility, strength and non-toxicity. He observed that when flooded, the resins would go where they were needed, finding and filling the fissures and cracks that, along with broken lugs and keys, are the cause of failing plaster. This flooding procedure was then followed by an application of a filled adhesive to replicate missing or broken keys and lugs.

After choosing a remote room in the Barnum house, Stewart cut out a small square of plaster from the ceiling in order to have a “before” sample. He then “flooded” the back of the ceiling with two applications of acrylic adhesive—one diluted to act as a primer.  Twenty-four hours later, after the adhesive had dried, another square was cut out of the treated ceiling.

“The results were astonishing, far exceeding our expectations,” Stewart recalls. “Our primary objective was to adhere the plaster to the wood lath. That in itself was a great success. But we also found that not only did the resins fill the fissures and cracks but they infused the plaster matrix and made it significantly stronger. When we compared the before-treated sample with the after-treated sample, the difference was like night and day.”

The Remote Consolidant Applicator

After a number of commercial successes with his new method, Stewart coined the term “plaster consolidation” to describe what his treatment method achieves. “As far as I know, we are the first people to think of converting a plaster ceiling from being a suspended, mechanically hung system to being a unified, consolidated, adhered system.”

In 1985, Stewart formed Historic Plaster Conservation Services Limited.  Over the years, Stewart has modified the Phillips’ acrylic resin-based formulas to improve penetration into the plaster, and along with his partner and wife, Masumi Suzuki, has developed a roster of plaster conservation products that not only consolidate plaster systems but address virtually every conceivable challenge that fragile plaster can present.

Stewart has also invented a number of extraordinary tools, including HPCS Micro-Jacks to gently lift detached sections of a ceiling back into place, and the HPCS Remote Consolidant Applicator that can apply consolidation products to the backside of plaster from a blind location when there’s no access above the ceiling. He also invented and patented a double-chambered cartridge that enables the user to mix the Phillips’ filled adhesive formula directly within the cartridge rather than having to formulate the material in a bucket on site.

In 2010, he developed a new product comprised of acrylic resin and Dupont Kevlar that has been used to successfully stabilize and reinforce the fibrous plaster coffered ceiling panels in Frank Woolworth’s office in the Woolworth Building in New York.  There are thousands of fibrous plaster ceilings in America, and just like their earlier plaster-on-wood-lath cousins, they too are approaching the end of their maintenance free life span and need to be addressed.

“One of the most rewarding challenges in the field of heritage conservation,” Stewart states, “Is to anticipate an endemic problem and develop systemic solutions that will allow future generations to enjoy these remarkable assets.”

To date, the HPCS method and products have been used to consolidate or reinforce more than 100 plaster ceilings in important buildings in the United States and Canada, including the Lower East Side Tenement Museum (New York), St. Patrick’s Old Cathedral (New York), Iviswold Castle (Rutherford, New Jersey), Alexander Hamilton House (New York), Old City Hall (Toronto), the New Brunswick Legislature (Fredericton) and the Prime Minister’s Residence (Ottawa).

When asked to succinctly describe what HPCS does, Stewart replies, “We extend the useful service life of fragile plaster ceilings in historic buildings.”

Some of the HPCS plaster consolidation projects are now more than 30 years old. Last year, Stewart visited a few of them to see how the ceilings were holding up. “They’re as good as the day after we treated them. No additional cracking and no deterioration. I would bet they will still be in great shape 100 years from now.”