The five-story Cadena-Reeves Justice Center in San Antonio turned heads when it was completed in 1988. Pecos Red sandstone trim around windows, arched entrances, and under-roof overhangs accented the Texas Cordoba Cream limestone walls to lively effect.
But weather and water had other plans. It repeatedly wetted out the limestone, which had trouble drying in the South Texas humidity, especially on the north and east elevations.
Within a few years, green and black biological stains spread on the once-pristine stone. The moisture also helped particulates penetrate the stone, graying out its cheerful color.
But it was the bleeding that made people look twice. Water streamed down the walls in places, leached iron oxide from the sandstone, and deposited it in long orange sheets and fingers on the limestone.
“That's not the image the justice center wanted to project,” says Mackey Welch, vice president of One State Contractors, Buda, Texas. Welch and his crew were charged with cleaning and repairing the building's exterior fabric. They were part of an effort led by VITETTA, a Philadelphia architectural and engineering firm.
The project took a first step in spring 2007 with an onsite evaluation by VITETTA masonry specialist, Nan Gutterman, who investigated with a hand-held microscope, and tested various cleaning methods. Stone samples were sent to AMT Laboratories in Lawrence, Kan., for water-repellency testing.
Gutterman found that the staining, though vivid, had not penetrated deeply into the stone. She specified both general and specialty cleaners for the building.
In late 2007, One State Contractors began scraping off the urethane sealer over the building's mortar joints. The sealer was due for replacement, and VITETTA needed to assess the condition of the joints.
The crew hand-scraped and hand-sanded miles of joints. Noisy power tools weren't allowed, as the justice center remained open throughout the project. Underneath, the joints were in remarkably good shape, so no tuck-pointing was needed. A Dow-Corning silicone sealer replaced the worn urethane.
After a 10-day cure in early 2008, the first of three cleanings commenced.
Getting rid of general dirt and grime that could interfere with the more specialized washes to come was task one. Workers used Enviro Klean 2010 All Surface Cleaner from PROSOCO, which contains several detergents and surfactants.
The cleaner has no harsh acids, caustics, or solvents, but it does contain chelating agents. Chelating (from Latin “chela” for “claw”) agents are molecules that can pull some contaminants, including some metallic staining, out of masonry pores too small for many other cleaning molecules.
With dirt and grime gone, the workers focused on the biological staining on the red sandstone. Using a bucket and brush, they gently scrubbed the stone with Enviro Klean BioWash, a mild cleaner made for light-to-moderate biological deposits.
Results were immediate, as the cleaner released the dark colonies for rinsing away with a maximum 400 psi pressure wash. A sprinkler system wet the surrounding limestone to keep the spent cleaners and dissolved contaminants from soaking in as it ran down the walls.
None of the 4000 gallons of rinsewater per day hit the streets. A vacuum boom collected the rinsewater, which usually measured about 7 to 7.5 pH, before it was released to the sanitary sewer.
The third wash took aim at the biological and pigment staining on the cream-colored limestone. Workers used Enviro Klean SafRestorer. a non-fuming, low-odor restoration cleaner, which uniformly dissolved the microscopic surface layer discolored by the red runoff.
At the same time, the cleaner broke the carbon-based bonds anchoring the biologicals to the limestone. “It looked like the day it was built,” Welch says.
Meanwhile, after testing several protective treatments on the stone samples, AMT Labs recommended Sure Klean Weather Seal H40. The penetrating, breathable treatment consolidates masonry and makes it more water repellent.
The idea is that a more cohesive and water-repellent sandstone will be less susceptible to water runoff. And if some limited iron-oxide runoff does occur, the water-repellent limestone gives it less chance to penetrate.
The stone also becomes much less hospitable to algae, mold and mildew, which need damp environments. The crew used pump-up sprayers to apply the H40 in three cycles of three coats each.
One State Contractors finished the justice center in late fall 2008. “We've received excellent feedback on the building,” Welch says. “Justice center employees, county commissioners, and even people just walking by have told us the building looks great. I like telling people I worked on this building.”
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