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After nearly 90 years, Duluth City Hall's walls get a deep clean

Walter Hankins, a technician with Premium Plant Services of Hibbing, uses air hose to shoot small, dry sponges at 40 pounds per square inch at the marble in the entryway of the Duluth City Hall Monday night. The sponges, which contain aluminum oxide particles, slowly and steadily remove years of stain and grime. Bob King / rking@duluthnews.com2 / 5
Tiny, gray-colored, granular sponges that contain aluminum oxide particles are used in the micro-abrasion process to clean grime from marble. Bob King / rking@duluthnews.com3 / 5
Walter Hankins, a technician with Premium Plant Services of Hibbing, uses air hose to shoot small, dry sponges at 40 pounds per square inch at the marble in the entryway of the Duluth City Hall Monday night. The sponges, which contain aluminum oxide particles, slowly and steadily remove years of stain and grime. Bob King / rking@duluthnews.com4 / 5
Walter Hankins (center) uses an air hose that blasts soft, sponge-like material to micro-abrade years of grime from the marble in City Hall Monday night. James Blight (left) sweeps up used abrasion material that will be re-used after a special machine removes dust-sized particles. DJ Reichensperger supervises at right. Bob King / rking@duluthnews.com5 / 5

Tari Rayala strode through Duluth City Hall, surveying wide-open spaces across the second floor and down into the first.

"Do take note of the white walls and how dingy they are," said the city's architect.

Then she turned a corner for the big reveal.

"It's so much brighter," she said from inside the entry hall along Fourth Avenue West as it radiated natural light.

For the first time since city hall opened in 1928, the natural stone walls that make up the first two interior floors are being given a proper cleaning. Yellowed and dulled like old newsprint, the travertine walls — noted for their bony whites and muted grays, and the elegant scars in the soft stone — are returning to a form first envisioned by the late Thomas Schefchik when he earned the commission in 1926 as one of the city's up-and-coming architects.

Rayala explained that decades of smoking inside the building and dirtier forms of heating, as well as skin oils from people rubbing against the walls, had robbed the stone of its pristine beauty.

The city council approved in April the nearly $107,000 restoration project. The work that began in late June is expected to take up to a month.

Important to preserve, "because they're part of our heritage," Rayala said, the walls have been entrusted to a Hibbing contractor using a state-of-the-art process that's being performed after dark.

Premium Plant Services is conducting the work using a special process invented by a New Hampshire company, Sponge Jet.

Mark Parenteau, CEO and owner of Premium Plant Services, and representatives of Sponge Jet were on hand last week to survey the early work.

"It's phenomenal," Parenteau said.

"I'm very pleased," said Ted Valoria, Sponge Jet's vice president for North America, who explained the process that, for this particular job, feeds aluminum oxide particles wrapped in tiny dry sponges through an air hose at 40 pounds per square inch.

Don't call it blasting, said Valoria, who noted the projection of the sponges offers a more delicate touch than sandblasting, which he added would have gouged the travertine.

"In historical preservation, it's called micro-abrasion," said Valoria, who works for the company that invented the sponge-fed process 27 years ago. It's been used in more than 100 countries around the world and boasts the White House as a client, said Valoria. It has applications that delve into industry and go far beyond cleaning walls, even though that's what New York City's famous Guggenheim museum used it for, too.

When asked why he made the business trip to Duluth, Valoria said, "It's a very high profile project for Duluth; I wanted to make sure we're supporting it."

Valoria praised Parenteau's crew, saying it was performing the techniques in textbook fashion, spraying the sponges like one would eat a corn cob — side to side, row by row.

"The workmanship is truly professional," Valoria said. "They've got an appreciation for the finesse that's required."

The work is noisy and dusty (though far less so than normal blasting), requiring it be done after hours. Parenteau's crew gets going at about 6 p.m. weeknights, setting up plastic sheeting for roughly two hours to keep the resulting dust from places it shouldn't go.

With heavy air hoses snaking the ground and the massive air compressor over his shoulder in the city hall garage, Parenteau grabbed a handful of the sponges from one of the many, hefty bags full of the reusable material.

"I compare it to being like an eraser," he said.

Parenteau explained his crew usually gets busy with the micro-abrasion work by 8 p.m. and wraps up no later than 5 a.m. By the time city workers arrive, there's no sign of the work or the crew — other than newly gleaming walls.

"I tend to be partial to history," Valoria said. "Being able to renovate and restore a place is the most appealing part of the process."

While city hall is part of a historically established district that includes the Federal Building and the St. Louis County Courthouse, it's the only building that's undergoing such a renovation at this time. With each building being funded and operated by separate government entities, there's no telling if or when further restoration efforts will expand into the other entities.

But Rayala is confident the results will be inspiring.

"Once they see what we've done," she said, "they'll be copying us."