By Lorayne Bryan

	Cleaning and maintenance restored Trinity Church to its former beauty. Photos courtesy of Gary Henry, PROSOCO

When builders constructed Manhattan's beautiful Trinity Church in 1846, they could not have envisioned that this ornate Gothic Revival sandstone structure, which then dominated the lower Manhattan skyline with its soaring neo-gothic spire, would someday rest in the shadows of some of the world's tallest buildings.

Nor could they have envisioned that the golden sandstone would need protection from the air and the rain, which would become increasingly polluted over time. Forty years later, conservators added a wax coating to preserve the beautiful sandstone (specifically a New Jersey brownstone), but whatever protection it provided was nullified by the tendency of the sticky surface to attract dust and dirt.

As the decades passed and New York City grew, industry contributed to the grimy buildup on the surface of the sandstone, and by the turn of the century, the golden beacon had become as black as the soot that often hung in the surrounding air. The stone remained dirty for so long that most New Yorkers came to believe that black was the historical church's natural color. Imagine their surprise when in 1990 the landmark church went from black back to its original light color in a matter of weeks. Initially, area police received reports from concerned locals that the church was being vandalized. The remarkable transformation/restoration was achieved with the application of appropriate stone cleaners made by PROSOCO, a family-owned Kansas company dating back to the 1930s.

According to Gary Henry, a spokesman for PROSOCO, its cleaners have been used to clean and protect landmark architecture across America — from the U.S. Capitol and the Pentagon to Dodger Stadium and the Walt Disney Concert Hall in Los Angeles. "We don't just make products and put them on the market," he says. "We provide a level of customer care unmatched in the industry, including technical support, free jobsite troubleshooting and training presentations. We offer quality products, but the most important ingredient isn't in the products — it's the people who stand behind them."

In the case of Trinity Church, PROSOCO experts conducted a careful analysis of the sandstone, gauging its fragility, and an analysis of the various components that had contributed to the dark buildup, which not only coated the stone but was imbedded in it.

"Correctly identifying and evaluating the stone fabric of historic architecture is the crucially important first step on the road to a successful project. Not all stone can be cleaned by the same type of cleaners, and there are specific cleaners for specific stains and imbedded contaminants and debris," Henry explains. For example, some types of stone tolerate aggressive acidic cleaners and some stone types will dissolve along with the stain if cleaned with acidic solutions — leading to etching, discoloration and even more significant damage.

Before it was cleaned, Trinity Church's sandstone appeared black. It had been dirty for so long, that many people believed it was supposed to be this color. Photos courtesy of Gary Henry, PROSOCO

One of the etched-in-stone rules of restoration is to identify every substrate on the building. In the case of Trinity Church, 150 years of bird droppings, mildew and environmental pollutants had significantly altered the appearance of the sandstone. It had long bore the patina of coal-operated boilers, soap factory smokestacks and Hudson River power plants. But old photographs and records depicted a lovely, light-colored façade. And the restoration team used definitive tests to confirm that the sandstone was indeed sandstone. That is not always the case. Although Chicago's Church of the Epiphany appeared to be made entirely of sandstone, apparently during construction, workers replaced crumbling sandstone coping stones with granite that looked similar. Granite, like sandstone, is a siliceous stone and can tolerate aggressive acidic cleansers, but coverage rates for the two stones are different. So the distinction between the stone types was significant.

While many industry professionals are able to visually examine stone and determine the composition, few are willing to stake their business solely on a visual identification. For the purposes of initial identification, industry professionals usually can determine if a stone is siliceous or calcareous based on color and appearance.

Commonly used siliceous stones — granite, sandstone and slate — are made mostly of quartz-like particles (silica). Some granite can be identified by the tiny mineral flecks uniformly distributed throughout the stone. This often is referred to as a salt-and-pepper effect. Varying mineral content creates the variation in granite color. Sandstone color varies according to mineral content as well, ranging from light gray and yellow to red and brown (New Jersey brownstone). Slate is usually dark green, gray, black or dark red and has a distinct cleft texture.

Calcareous stones frequently used in construction include marble, limestone and travertine. Limestone is the most widely used building stone in North America, with the Empire State Building being one of the most widely recognized examples. Typically, it is light gray in color and may reveal various fossils upon close examination. Marble varies in color according to its mineral content with high concentrations of colored minerals forming veins. Like granite, marble often is polished to a sheen, and this similarity sometimes leads to mistaken identity. Travertine is a sedimentary stone made essentially of calcite, deposited by calcareous waters. Its color is whitish, slightly yellow or reddish. Typically, it is used for floors or as a veneer. It is common in Tuscany, Umbria, Lazio and Marche, Italy. The Colosseum in Rome is likely the most well-known travertine structure.

Stone Restoration Guidelines Identify every substrate on the building. Use a proprietary cleaner from an established company that offers not only customer service, but tech support and jobsite and specification-writing assistance. Test the products thoroughly using the same conditions and variables that will effect the actual cleaning. Devise a plan for identifying the type of wastewater you will be producing and consult with regulatory authorities prior to beginning your project. Rely on the expertise of the product's technical support department rather than relying on your ability to guess.

For cleaning and treatment purposes, the most significant difference between siliceous and calcareous stones is that calcareous stones are much more sensitive to acidic cleaners. Another distinction is that many products used for consolidation and water protection on siliceous stones won't work on calcareous stones. To accurately ascertain which category a stone falls into, a simple acid test is used. A few drops of a 10-percent solution of hydrochloric acid will create a bubbling reaction on calcareous stone and little or no reaction on siliceous stone. Be sure to apply the solution to the bare surface of the stone (in an inconspicuous location) rather than on a sealed or polished surface.

Determining the type of stone being restored or cleaned is just the first analysis in determining which products are most appropriate for the project. Other considerations include: the fragility of the stone, what finishes currently are on the stone, whether the stone is polished or unpolished, and the density and porosity of the stone. When all points have been considered, and the appropriate products selected, a test application should be performed prior to proceeding with treatment.

After work crews striped off the layers of contaminants that threatened the building, and completed the cleaning treatment of Trinity Church, conservators assessed the condition of the New Jersey brownstone construction and elected to strengthen the deteriorating stone by applying stone-strengthening and water-repellent consolidation treatments. The treatments replace the stone's natural binding cement matrix lost to time and weather, essentially fortifying the façade and ensuring the integrity of the structure for perhaps another 150 years. On Sept. 11, 2001, the church was covered in smoke and pummeled with debris from the nearby World Trade Center disaster. Fortunately, damage was minimal, and the church served as a sanctuary for rescue and recovery workers. In the wake of Sept. 11, PROSOCO representatives volunteered as consultants in the architectural restoration and cleaning effort of Trinity Church.

The cleaning effort was minimal because of the earlier treatment of the stone. Unlike the 19th century wax coating that attracted grime and trapped water vapor, today's treatments are nearly 100-percent breathable, letting vapor out without letting liquid in, and without changing the appearance of the stone. "Water is the greatest enemy of stone," Henry emphasizes. "If allowed to penetrate into the story, it carries contaminants from air pollution into the stone. But the greatest threat to the integrity of the stone is caused by the freeze-thaw cycle — the expansion and contraction can damage the stone's structure. That's why using the proper protective treatment is so important."

So what are the recommended cleaning and protective procedures for the most popular construction stones? General parameters follow. However, get professional advice when necessary, and test the product on a small area prior to full application.

Granite and Granite Tile
Granite is extremely durable with an absorption rate often below 1 percent. Clean construction dirt from the surface and use a non-acidic cleaner for general cleaning. Sealing the surface with a film-forming sealer or coating is not recommended and a granite floor need not be finished either.

Honed Limestone, Marble and Travertine
Most honed limestone is extremely durable and scratch-resistant, however etching and oil stains from common household food products can present a problem. Do not use acid-based cleaners unless testing indicates that it is safe. A general, all-surface stone cleaner should work on most construction soiling, as well as grease and oil stains. Oil repellants are recommended. These can last up to two years on exterior applications and up to five years on interior applications.

Polished Marble, Travertine and Limestone
Polished marble (and travertine and limestone) though durable, is highly prone to scratching, etching and oil staining from common household food products. An all-surface stone cleaner is recommended for removing general construction soil, as well as grease and oil stains. Do not use acid-based cleaners as they will etch the stone. A penetrating oil repellent will help keep countertops new. Floor finishes are not recommended.

Sandstone Floors
With a wide range of colors and textures available, sandstone often is used for flooring. It can range from very porous to very dense, therefore, a consultation with your stone sales representative is recommended to help you determine the properties of your particular flooring. An all-surface stone cleaner will remove general construction soil as well as oil and grease. Sealing the surface with a film-forming sealer is sometimes desirable to prevent oil staining. Floor finishes often are used to prevent oil and dirt from penetrating the surface. Be sure and select a product that will not reduce slip resistance.

Slate
Slate is a durable stain-resistant flooring material that is easy to maintain. You can clean it with a general-purpose, all-surface stone cleaner. Most water-borne stains will remain on the surface of this dense stone for easy cleaning; however oil-borne stains may penetrate beyond the reach of most cleaners. Therefore, a film-forming sealer is often desirable, depending on the location of the flooring.

Numerous stone restoration and protective treatments are available for commercial and consumer use. With all the many variables that can affect product selection, it is advisable to work with a company that offers technical support and even onsite evaluation and instruction.

Lorayne Bryan is a freelance writer.

Resources
For more information, visit these Web sites:
www.prosoco.com
www.bellinzoniusa.com
www.stonetechpro.com
www.tenaxusa.com
www.filachim.com
www.inland-inc.com
www.drytreat.com
www.glaze-n-seal.com

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