On the morning of Sept. 11, 2001, Haywood Miller's crew was finishing work on the limestone exterior of Wedge One - the Pentagon's southwest-facing corner.
"I had two people on the roof and one inside," said Mr. Miller, operations manager for Forestville, Md.-based MBS Inc., a masonry restoration firm. "The rest were on the ground."
Then the unimaginable happened. At 9:38 a.m., Flight 757, hijacked and carrying 64 people and 10,000 gallons of fuel, slammed into the west side of the wedge. Along with the passengers, crew and hijackers, 125 people in the Pentagon died. Hundreds more were injured.
The MBS people were all on the south side of the wedge, Mr. Miller explained. Luckily for them, they happened to be at the jobsite's furthest point from impact.
"They were bruised and scraped," said Mr. Miller, who had left the job site at 8 a.m. to attend a meeting, "but they survived. And for that we're very, very grateful."
Mr. Miller and his crew had spent the summer of 2001 cleaning, patching and tuckpointing the 71,000 square feet of the Wedge One exterior. Their work was part of an overall $1.2 billion Pentagon renovation, inside and out, due to be completed in 2014. They encountered the usual soiling found on aged urban masonry, Mr. Miller said. Carbon, water stains and dirt.
For most of the project, they used Sure KleanŽ Limestone Restorer, an acidic cleaner for moderately dirty unpolished limestone. The restorer works by uniformly dissolving the thin, stained outer layer of the limestone. Workers applied the cleaner with garden sprayers and lightly scrubbed the treated surface with nylon brushes. They rinsed away the dissolved staining and the spent cleaner with high-pressure water.
Where staining was worst, such as under windowsills, the crew used Sure KleanŽ 766 Limestone & Masonry Prewash, followed by Sure KleanŽ Limestone & Masonry Afterwash. The two-step treatment uses an alkaline prewash to break up tough soiling, followed by the mildly acidic afterwash that neutralizes and brightens the cleaned surface.
"The products worked great," Mr. Miller recalled. "Our results were good and the Pentagon officials seemed happy with the way the stone looked."
MBS's facade cleaning of Wedge One capped a major milestone in the renovation. It was one of the final steps in the three-year renovation of the wedge. The wedge itself, one of five Pentagon sections, represented 20 percent of the project. Done.
And in a few catastrophic seconds, undone.
Between then and Jan. 1, workers labored 24/7, refusing to take holidays. Even now they work six days a week in 10-hour shifts. The effort is nicknamed "Project Phoenix," after the mythical bird of fire that rises from the ashes of its own destruction. Crews have cleared away wreckage, put up support columns, poured concrete.
They are racing the clock to have the exterior "E" ring of Wedge One rebuilt and re-inhabited by Sept. 11, 2002. It's a real clock. A big digital clock with the words "Let's roll" emblazoned across the top lets the crews know, second-by-second, how much time is left. Workers are shooting to have the wedge entirely repaired by Spring 2003.
Congress has added $300 million to the renovation budget, to speed up overall completion from 2014 to 2010. The repair of Wedge One alone is budgeted at $740 million.
The job of salvaging and cleaning the damaged limestone facade around the point of impact fell to Bessemer, Ala.-based MasonryArts. MasonryArts had just finished installing the blast-proof windows in Wedge One that were widely credited with helping to limit the attack's destruction.
The task required workers to take the burned and blackened stones off the wall, and clean them in a secured parking lot. The facade stones, 5 feet long, 2 feet wide and half-a-foot thick, each weighed about 600 pounds. Larger stones from the cornice above the fifth floor windows weighed between 4 and 5 tons each. Some stone was too damaged and had to be discarded. The MasonryArts crew cleaned the stones with EnviroKleanŽ Degreaser, an industrial-strength multi-surface detergent. Applied in concentrate and pressure-rinsed with clean water, it stripped away thick coatings of black carbon and jet-fuel residue.
The degreaser utilizes "chelating" (key-late-ing) agents, a technology that's been known for some time, but that's only now beginning to show up in the pressure washing industry.
Chelating agents are molecules that chemically latch onto the atoms of tiny contaminant molecules, like the jet-fuel residue on the Pentagon limestone. The term comes from the word "chela." A chela is a pincer-like claw, as on a lobster or crab.
Instead of drawing the tiny contaminants out of the limestone pores like a poultice, or emulsifying them like a surfactant, the chelating agents go in after the particles, where the bigger molecules of detergents can't reach. But the particles can't escape the "tweezer-like" chelating agents. They grab the rust particles and suspend them in solution, to be rinsed away.
Chemically what's happening is that metal ions in the contaminating molecules are irresistibly attracted to charged molecules in the chelating agent. Since molecules come in structures like rings or chains, when the ions bond, the contaminating molecules are pulled away from the surface and bound to the chelating agent.
Scientists have known about chelating agents for decades, but the technology has only recently been applied to cleaning. It has widespread application, from spot-cleaning laundry stains to cleaning skyscrapers.
Some of the stone was splattered with melted roofing tar. Solvent-based Sure KleanŽ Asphalt and Tar Remover was approved for that cleaning task.
By April, MasonryArts workers were putting the stone back on the poured concrete walls, both salvaged stone and newly quarried replacement stone, trucked in from Indiana.
The new stone came in on 50 flat-bed trucks, said MasonryArts Project Executive Roy Thompson. Each load of light-gray to buff-colored limestone weighs about 20 tons.
"The original Indiana limestone we salvaged is excellent material," Mr. Thompson said. "It looks as good and will perform as well as the new stone. After all, it came from the same place."
Like everyone else at the job site, the MasonryArts crew hustled to meet the Sept. 11 goal.
"There's a definite sense of urgency," Mr. Thompson commented. "It's fueled in large part by patriotism. I can't publish the schedule, but I can tell you we're ahead of it. We'll make that Sept. 11 goal. There's no doubt it will happen."
On June 11, exactly nine months since the attack, workers reattached the last limestone block. It was a salvaged stone, burnt and discolored, but still whole and strong, and purposefully not cleaned. It capped a niche in the facade, for a special dedication capsule. Inside the capsule - hundreds of cards and letters from school children, a plaque with the names of all 184 victims, Arlington County police and firefighter badges, and more.
The stone is inscribed with the date of the attack.
A final cleandown with Sure KleanŽ Vana Trol before the Sept. 11 deadline is the last step in the facade restoration. MasonryArts will try to duplicate, as closely as possible, the results achieved earlier by MBS.
MBS, meanwhile, is eagerly awaiting the call to take up where they left off. With Wedge One complete, MBS will join MasonryArts in renovating Wedges Two through Five, according to Mr. Miller.
"As MasonryArts gets the blast-proof windows in, we'll follow along, cleaning and repairing the facade," Mr. Miller said.
Though normal practice is to clean before installing windows, the procedure is reversed in this case.
"Replacing the windows involves some pounding to get the old windows out," Mr. Miller explained. "That could affect our patching and tuckpointing.
"I always wanted to work on the Pentagon," said Mr. Miller, who is in his 25th year in the industry. "I wanted to add it to the list of historic buildings I've worked on.
"My feelings go way beyond that now," he said. "This is something that will go down in history. It's a privilege to be part of that."