masonry, stone, brick, chimneys

Terra Nova

A careful investigation of the conditions is required before recommendations can be made for treatments to repair architectural terra-cotta surfaces.

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By Nicole V. Gagné

To date, Chinese archaeologists have unearthed more than 7,000 life-size statues – soldiers, horses, chariots – dating from the Qin Dynasty (221-206 B.C.). These marvels were made not of stone but of terra cotta, a fired clay that achieves a hardness and endurance rivaling stone. Terra cotta’s central importance in the ancient world’s sculpture and pottery was so fundamental that it’s easy to overlook the equally vital role this material played in the bricks and roof shingles of construction. As a thrifty substitute for carved stone, terra cotta eventually became a prominent feature of exterior ornamentation in Western design and made its presence felt in American architecture.

“Its first use in the United States happened in the late 1840s and ’50s,” says Susan Tunick, president of Friends of Terra Cotta (FOTC), a national non-profit organization founded to promote education and research in the preservation of architectural terra cotta. “Terra cotta was made by small companies that tended to be from the East Coast. The main development, what we call the second revival of terra cotta in the United States, took off in Chicago after the fire of 1871. As this phase developed, there were Midwest, West Coast and East Coast companies. The real period of popularity would be from the mid-1880s until the late 1920s, when the Depression hit. Changing tastes and developing technologies also lessened the use of terra cotta, but the main impact was the fact that fewer buildings were being built in the Depression.”

FOTC has performed a great service in encouraging the restoration of exterior terra cotta. “Our organization has been in operation for 25 years,” says Tunick. “In the early ’80s, there were only three or four New York projects that used new terra cotta for restoration. Now there’s got to be at least 150. We’ve seen a very steady increase in the use of actual terra cotta for replacement. Proper, in-kind repair becomes more economical if you’re able to look at the long view.”

Among suppliers of true terra cotta, two internationally respected and sought-after firms are Gladding, McBean of Lincoln, CA, and Boston Valley Terra Cotta of Orchard Park, NY. Neither business restores damaged terra-cotta ornament; they only create pieces that follow new designs or replicate earlier work. But experts with both firms agree: When vintage terra cotta suffers damage and requires replacement, the fault does not lie with the material.

“Terra cotta doesn’t fail,” insists Gretchen Krouse, vice president of sales and promotion at Boston Valley Terra Cotta. “It’s fired at 2,000 degrees, and it actually lasts longer than stone because it doesn’t deteriorate.” Pete Pederson, national terra cotta sales manager for Gladding, McBean, echoes her. “Terra cotta has an unlimited life expectancy,” he says. “The typical reason for its replacement is moisture intrusion, brought about by faulty joints or flashings or improper installation procedures, such as using incorrect anchoring systems – or a lack of any anchoring systems. In many areas, severe weather problems cause expansion and contraction during freeze-thaw conditions. In other areas, you have salt-water conditions that will affect the anchoring and the actual building.”

Krouse knows the spots where terra cotta fails most frequently. "Down the corners of the buildings," she explains, "up in the parapet area, around the windows, where water can collect. It starts rusting the steel, and the steel expands and breaks the terra cotta.”

“It boils down to the era in which the building was constructed,” notes Jim Anderson, marketing manager at Gladding, McBean. “Earlier buildings used steel or galvanized anchors instead of the later stainless-steel anchors, and these erode over time.”

Not surprisingly, the older systems for anchoring terra-cotta pieces are still preferred today, although the materials comprising them have changed over the years. “The engineering hasn’t changed a whole lot,” Krouse explains. “And of course we don’t make the attachment systems. We tend to go with what the engineer or architect designs. But the methodology of anchoring and hooks is still pretty much the same, only stainless steel is the preferred anchoring-system metal now because it won’t rust.” These replacements sometimes extend further than the old anchors, notes Pederson. “The actual substrate or original steel structure can deteriorate to the point where it has to be removed and replaced along with the old anchoring devices. But in some instances, the substrate or the original steel can be cleaned to a degree that it can be coated and reused.”

Just as anchoring methods have survived more or less intact, the terra-cotta formulations currently in use are also largely those of an earlier era. “Boston Valley Terra Cotta is run by a ceramic engineer,” Krouse points out, “and our terra cotta has been formulated and engineered to withstand freeze-thaw, so its ability to last many, many generations is outstanding. But it’s still pretty much the same, just better quality, more refined, so you don’t have inert materials in there.”

Terra cotta from Gladding, McBean, according to Pederson, “is formulated to be greater than specification requirements for moisture absorption, saturation coefficient, compressive strength and freeze-thaw conditions. The materials manufactured today are of better quality than, say, a hundred years ago, because the firing process is now much better controlled. Many of the kilns are computerized and controlled with a more accurate temperature gradient.”

Of course, true terra cotta is no longer the inexpensive item it once was; the more complex the replication, attachment or both, the greater the cost. “Prices vary greatly with the degree of difficulty in producing the units,” comments Anderson of Gladding, McBean. “The minimum would be a flat piece, maybe $75 or so per square foot.” Krouse of Boston Valley Terra Cotta didn’t offer a minimum, saying instead that “there’s definitely some basic square-footage costs, but each project is different because you have to start out with new models and molds to match that existing building.”

Both firms can also require a significant lead time for their work. “Lead times vary with the size of the job, how many models and molds. It could be five or 105. But I would say an average is 12 to 14 weeks,” says Krouse. “We can start on the project as soon as we have access to the building,” notes Pederson. “But the preparations that lead up to the actual receipt of the replacement materials can be quite a lengthy time frame.” These suppliers also offer secure warranties for their terra cotta, contingent upon the installation and the original design specifications of the project architect.

Substitute Materials
Meanwhile, suppliers of substitute materials such as GFRC (glass-fiber-reinforced concrete), cast stone and fiberglass agree on the characteristics of true terra cotta, while offering alternatives. “The biggest problems are usually never with the terra cotta; it’s the steel behind it,” says Philip Gallagher, president of Towne House Restorations, a Brooklyn, NY-based supplier of cast stone. Charles Wittman, president of Architectural Fiberglass Corp., of Copiague, NY, a supplier of fiberglass, agrees. “Typically, the problems with terra cotta are caused when water gets in and corrodes the structural steel and the steel hangers – or, in many cases, the cast-iron or wrought-iron hangers and straps.”

David Talbott, president of Architectural Reproductions, a Portland, OR-based supplier of GFRC, expands the problem list, observing that people can be as destructive to terra cotta as water can. “Wear and tear and changes of styles are the most common problems,” he says, “such as storefronts torn out and modernized or cornices that have fallen because of lack of maintenance.” However, Talbott has also seen situations where the original material carries some of the blame. “We’ve also replaced terra cotta that has not weathered tremendously well. Like other materials, terra cotta took a while to evolve, and in some earlier installations, it’s not unusual to see stress cracking because of a heavy compressive load and insufficient stress release in the wall. That’s a problem with learning to use the terra cotta, but one problem that’s hard to attribute to anything but the terra-cotta piece itself is glaze failure.”

Substitute materials have stimulated new approaches to anchoring replacement ornament. Talbott notes that, with GFRC pieces, attachments still employ “the flex-anchor situations. But there are variations in what was done with original terra cotta, with holes that go entirely through flanges and webbing, and stainless-steel rods that might be used. There is the potential to use a cut, slotted, kerfed connection with a stainless-steel strap anchor, much like is used in stone masonry. We’ve done a lot of work and a lot of testing of those connections. Flexibility in the mounting systems, even with smaller pieces and premix materials, is still desirable. Molding things down rigidly is typically not a very good idea.”

Wittman attributes a special advantage to fiberglass because “it’s extremely lightweight compared to terra cotta. So there have been cases where the steel supports were inadequate to support the terra cotta, but the engineer has been able to adaptively reuse the original steel spandrels and outriggers to support the fiberglass. If they were redoing it in terra cotta, they would have to completely redo all the steel.”

Cast stone is a different story, as Gallagher explains. “The anchoring usually changes considerably because we’re putting in solid blocks," he says. "The terra-cotta pieces were hollow, and they would backfill them with masonry; and that masonry would attach into the masonry back-up conditions and oftentimes interlock the piece with the building itself. We usually use a different type of anchor to anchor back into the masonry: all stainless-steel clips and pins with epoxy or expansion bolts that will tie to the back-up masonry or be welded to the back-up steel.”

Gallagher points out that “roughly 80 percent” of Towne House Restorations’ work involves the replacement of terra cotta. “The majority of it being probably water tables, header stones, lintel units – the areas where they mostly have steel," he says. "I give a ten-year guarantee on my products, although I’ve done jobs 16 to 17 years ago, which still look mint. But concrete certainly won’t last as long as terra cotta.” The real advantage to using cast stone, he notes, is the cost. “Terra cotta is usually over 50 percent more expensive. Also, it usually takes twice as long to get the material; there aren’t a lot of terra-cotta companies, the demand is great and the client has to wait longer. For most jobs that we do, it’s only about eight to 10 weeks before we can start providing product.”

At Architectural Reproductions, replacing terra cotta accounts for “close to 50 percent of our work,” according to Talbott. He credits this frequency to innovations in GFRC formulation. “A decade ago, we tended to see GFRC as a little too complex for a lot of terra-cotta replacement. What changed our approach was a change in the technique. Traditional GFRC was nominally a half-inch thick – a very thin-shell material. But this new evolution of GFRC is a hybrid material, about an inch thick. It’s called premix material. This thicker, heavier GFRC is quite comparable to terra cotta itself in terms of wall thickness and would even at times have interior webbing within the parts. It ends up having physical properties much closer to terra cotta – weight, an ability to handle even in a semi-structural capacity. True GFRC is a cladding only, with no real structural capacity. But the premix variation has different glass contents and admixes within the concrete, enabling it to gain significant strength. There are still very particular engineering requirements in terms of attaching stuff. But now we can make individual parts, or we can consolidate two or three parts into one molding with false joints, for example.”

These developments, Talbott believes, are responsible for the growing reliance on GFRC when replacing terra cotta. “When substitute-materials producers like ourselves can take molds off original parts, we can offer very substantial savings, 50 percent or more over terra cotta,” he says. “Without coatings and even without maintenance – and it’s safe to assume that lots of buildings aren’t maintained after installation – the margin for error with GFRC is quite large. With some other materials, FRP or in some cases polymer gypsum, if things aren’t installed the way they were intended and designed and engineered, they’re likely to fail sooner than the premix GFRC.”

Wittman estimates that the frequency of Architectural Fiberglass’s terra-cotta-replacement jobs at around “20 or 30 percent,” due in part to the savings in lead time over true terra cotta. “I have no idea what the actual terra-cotta costs are, but I know they’re significantly more,” he says. “Sometimes people are willing to pay more just to get it done. But the lead times for terra cotta can be long; their product might be cheap, but if you can’t get it, it’s no longer cheap. Typically, the installed cost of the fiberglass is a considerable advantage over the terra cotta. And this stuff is going to be up there long after we’re gone. Fiberglass is an inert material. It doesn’t rot. It doesn’t corrode. It doesn’t rust. It doesn’t break down. You’re not going to have the kind of catastrophic failures you have with other materials. As long as the substrate is structurally sound and the fasteners are properly installed, it’s not going to fall off the building.”

When vintage terra-cotta ornament falls off a building, more than design work is lost – a piece of history is gone as well. But with the burgeoning of expert and responsible firms that supply true terra cotta, as well as those that produce appropriate substitute materials, the experience of history, which is the great gift of period architecture, can be reclaimed.

Click here for a list of terra cotta & terra cotta repair materials
Click here for suppliers of terra cotta replica materials
Click here for companies specializing in facade restoration