With the best of intentions, workers applied elastomeric coatings to the Ca­bildo around 1998 and the Presbytère in 2004. Around the same time, the Old Ursuline Convent in New Orleans and the Old State Capitol in Baton Rouge received similar applications. But what was first seen as a state-of-the-art technique soon turned out to be a preservationist’s nightmare. As it turns out, exterior masonry and stucco require a certain amount of moisture to main­tain their structural integrity; without it, the exterior cracks and crumble.

“Elastomeric coats are designed to exclude water from buildings, and in theory they don’t cause problems as long as all water is excluded from en­tering a building. But that is impossible to do,” said Cangelosi. “Water can come from rising damp, hairline cracks, movement, interior sources includ­ing condensations, failure of adhesion of the stucco and other sources. And once in the moisture is in, it cannot escape, as the coating is designed to prevent the transmission of moisture.”

Trapped behind the paint, this moisture has no place to go except through the building’s interior plaster walls. But before this was realized, damage had been done. The Old Louisiana State Capitol building was one of the earliest buildings in Louisiana to report damage after it was discovered that the elastomeric coatings had been the culprit behind decay caused by trapped moisture within the building walls.

“Historic buildings and their fabric must be able to breathe,” Cangelosi said. “History has shown that any product which prevents that will have an adverse effect.”

Elastomeric coatings did not go from panacea to poison overnight, of course. But by 2005, the Vieux Carré Commission (VCC) rejected the Ur­suline Convent’s request to repaint an elastomeric fence. Staff analysts con­cluded that such paints “are disastrously inappropriate for historic masonry walls and structures in all high humidity/high temperature climates and especially in sub-tropical and tropical climes like New Orleans.”

These words proved prophetic, and work to remove the elastomeric coat­ings on the Cabildo and the Presbytère began in 2014. By that point, the dam­age done to those buildings by the coatings was severe. “”I received a video early one morning from someone passing the Cabildo as parts of it literally were exploding off the building as the trapped moisture was trying to escape,” Cangelosi said. “Not only did it cause extensive damage to the building, but someone could have been seriously hurt.” Koch and Wilson Architects was selected to oversee the work of associated waterproofing at the Cabildo, and Jahncke & Burns Architects was chosen as the architect of record for the work of advanced waterproofing at the Presbytère. Associated Waterproofing is the contractor of work on the Cabildo, and Advance Waterproofing LLC served as general contractor for the Presbytère‘s first phase of work.

At first, the plan was to remove the coating from only the front façade of each building. As the work proceeded, however, it quickly became clear that not only would the other sides of the buildings need to be stripped, but that stucco and masonry underneath the elastomeric coatings had suffered extensive structural damage and would need repair.

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