The Iglesia de San José in San Juan, Puerto Rico, is one of the oldest and most architecturally significant structures in the Americas. Built by Dominican friars in 1532, the church—which housed the remains of Ponce de Leon for some 300 years—is widely considered a masterpiece of Spanish Colonial architecture.

“It’s a huge Gothic and post-Gothic masonry church; a very significant building given that it’s one of the earliest expressions of this style in the New World,” says Matero. Despite its rich history, the church had fallen into such disrepair that it was closed to the public and placed on a watch list of endangered historic sites. Decisive action was needed.

At the behest of the World Monuments Fund, and in collaboration with the Polytechnic University of Puerto Rico, the National Park Service, and other institutions, the ACL responded with a campaign of emergency stabilization measures.

“A whole series of our summer and post-graduate interns have been involved with this project and have had an opportunity to bring their training to it,” says Matero.

One of the most distressed parts of the church was a domed chapel dating from the 17th century, the Capilla del Nuestra Virgen de Rosario. Years of water infiltration had badly weakened the interior plaster, threatening to turn a series of historic mural paintings into a pile of rubble. The Penn team and its partners quickly arrested and repaired the damage by injecting special grouts and adhesives into the weakened areas, ensuring the survival of the plaster—and paintings—for generations to come.

An intriguing question then arose—what had caused the roof to leak in the first place? The answer proved pretty decisively that new does not necessarily equal improved. As Matero and his students began to examine the layers of protective coating on the dome’s exterior, they made an interesting discovery: Later layers were white; earlier layers, red. Laboratory analysis showed the white to be portland cement, a British invention of the early 19th century that is now the world’s most commonly used cement. The red layers, though, were something entirely different.

“It turned out to be lime mortar mixed with brick dust,” Matero explains.  “The brick dust made the mortar hydraulic, which is to say waterproof, and it’s a perfect material to use in the humid environment of Puerto Rico, where traditional lime mortar won’t set and the good flexural strength of the lime makes this waterproof skin flexible as the dome expands and contracts.”

This elegant, low-tech solution goes back a long way.

“The Romans actually invented this technology,” Matero explains. “It came to the New World by way of the Spanish because it had been used extensively on the Iberian Peninsula. So now this masonry tradition hybridizes into something completely New World.”

As it turned out, the red mortar didn’t just look better, it worked better.

“We know now that the artificial cement was largely responsible for the water damage,” Matero says. “Such materials have wreaked havoc on these types of buildings. They’ve caused leakage from cracking and water entrapment; they’ve changed the historic appearance; and they perform totally unlike the traditional masonry that comprises the structural aspects of the buildings.”

Having arrived at this conclusion, Matero and his colleagues learned all they could about the composition of the mortar, and even found ways to improve it slightly. Then, working with a group of local masons, they set about reproducing it.

“It’s been the input of many, and we’re finding it’s really working,” says Matero. “So we’re about to—hopefully—change the face of San Juan by reintroducing this material that has been lost for many years. It will make the domes red and white again in an ornamental way, but it also has to do with function.”

Furthermore, it provided an environmentally friendly solution—at a reasonable price.

“Everyone is talking about sustainability, with respect to food, in terms of local produce,” says Matero.  “Well, the costs of restorations are often skyrocketed by the need to import materials from very select places. That is not true in this case, given that we’re using local materials. This technique introduces a new notion of sustainability, using traditional technology based on recycled materials such as used bricks for waterproofing, which had been abandoned with the advent of cement, and even later, membrane coatings, which are based on the oil industry.”

In addition, the ACL’s work on the Iglesia de San José should spark new research. Matero outlined his findings in a paper given in Lisbon last September, and hopes to conduct further research in conjunction with the Getty Conservation Institute.

“When something like this happens, I realize that it’s really why I do this,” he says. “History showed the way.”

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FEATURE:
The Future of Our Past By David Perrelli

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Three degrees of stabilization: The Iglesia de San José’s Rosario Chapel before it was stabilized by the ACL (below); the chapel’s dome murals during treatment (middle); a digital reconstruction of the chapel in the 17th century (bottom).