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Terra Cotta Repairs: Navigating the Challenges and Safety Concerns

Dane Barnes
Joseph K. Blum Co.

“Cracks in terra cotta can imply much more significant damage underneath — and pose a dangerous hazard” 

Facade repairs are a never-ending challenge, but add in the unique requirements of terra cotta and the stakes become higher. From replacement questions to Landmarks Preservation Commission oversight, projects that may have started out as a minor repair can quickly grow into a major one. Dane Barnes, a partner at the engineering firm Joseph K. Blum, recently helped one Upper East Side prewar co-op on Fifth Avenue navigate its way through the terra-cotta maze.

When a Crack Is More Than a Crack

While performing a routine facade inspection at the co-op, Barnes found a number of cracks on the cornice, which was made of terra cotta. A decorative design element, cornices are part of the masonry that sticks up above the roof. “Many people think of them as parapets, but cornices have an additional component because they actually cantilever out and over the sidewalk,” he says. At this 14-story building, the cornice spans 150 to 200 feet across the width of the front facade. 

The reason cracks in terra cotta can be cause for alarm is that they can imply much more significant damage underneath. “Think of it like clay pottery — terra cotta is hollow on the inside and only about 1 inch thick, so when you start to see cracks, they probably penetrate through the entire thickness,” Barnes explains. Because terra cotta is heavy and cannot cantilever without additional support, it is held up by a steel substructure of angles and threaded rods that are tied to the building’s structural skeleton. Over time, water penetrates terra cotta, typically through the joints, and the steel substructure becomes exposed to water, causing it to rust. As a result, deteriorated terra cotta can pose an extremely dangerous hazard.  “When steel rusts, it increases in volume and pushes outward, causing cracks in the terra cotta,” he says. “Unfortunately, that can cause pieces of terra cotta to fail suddenly and unexpectedly. A piece that falls from the building could easily weigh 10, 20 or 30 pounds. So these are things that can be lethal.”

A Zoom Show-and-Tell Session 

It’s one thing for an engineer to tell you that you have a potentially serious problem. It’s quite another to see it for yourself. In order for the board to actually see the extent of the issue firsthand, Barnes arranged a show-and-tell. Using Zoom, Barnes had the operator of a boom truck show board members the damage up close. “I directed the operator to move to various points where we had seen some concerning conditions, and I explained what was going on underneath the facade,” he says. In a number of locations, the operator was actually able to remove chunks of crumbling terra cotta with his own hands. “When they see that, people often think, ‘Well, stop that. You’re causing damage to the building,’” Barnes says. “But we’re gentle when we’re doing this. When you lightly tap a section and a piece of stone falls off, it becomes very obvious how serious the problem is. Also, a moving image helps people understand scale. Boards don’t have to simply take our word on this.” 

Choosing Between Patch Repairs and Replacing Terra Cotta

Terra cotta is a strong, durable material, but after 100 years — which is roughly the age of the building — it inevitably starts to fail. “Once it does, there are really no good options for repair,” Barnes says. “You can patch it, but I really don’t like to patch terra cotta because being hollow makes it really hard to be sure that you are creating a sound patch. It’s easier to patch limestone or cast concrete because the material is solid all the way through and the patch has a good bond to the rest of the stone. There’s no way to ensure that with terra cotta.” 

Like many prewar structures with terra-cotta design elements, this was a landmarked building, which posed another knotty problem. The city’s Landmarks Preservation Commission requires terra cotta to be replaced with identical, matching materials. But when replacing terra cotta with terra cotta in kind, costs soar, and repair time often drags on and on. There are only two facilities in the U.S. that produce and replicate terra cotta for architectural facades. Boards must send them pieces of undamaged terra cotta so molds can be created to cast new ones, which are shipped back. That can often take as long as 12 months because there are long waiting lines for both manufacturers.

Barnes brainstormed an alternate solution: replacing the damaged pieces with glass fiber reinforced concrete, also known as GFRC. “It has a steel substructure and has a similarly thin shell as terra cotta, and to the layman, it looks identical to the real thing,” says Barnes, who rejected another option, fiberglass, which can fail sooner than GFRC. 

The new material solved two problems in one. The concrete pieces could be tied to the building’s structural skeleton and welded in place. And because it’s lighter than terra cotta, GFRC offers an additional benefit. “We had originally proposed replacing the cornice all the way down to the window heads of the top-floor apartments, which also had terra-cotta design elements ­— in this case, decorative semicircles with masonry in between that would also have to be replaced,” Barnes says. “Being so light, it wouldn’t impose any structural load onto the material below, so we could preserve the terra cotta there.” The board approved, and the LPC also gave its stamp of approval. 

Terra-Cotta Repairs Are Expensive, but You Can Reap Big Savings

The project cost is significant, but by using GFRC instead of terra cotta, the board will save an impressive $500,000. “When we see these kinds of conditions that can look minor to the untrained eye, our heart sinks because we know we’re going to have to give bad news to the board,” Barnes says. “We don’t have any interest in finding big, expensive and difficult projects for buildings. The obligation is always first and foremost to public safety and the people walking underneath these cornices. If people are reluctant to replace their terra cotta, I always say, ‘Who are the ones walking underneath your building more than anybody else? You, the people who live there.’ They usually get on board when they hear that.”

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