Sponge Media Restores University Capitol Building


Global manufacturer of dry, low dust, recyclable abrasive blasting media and related equipment Sponge-Jet (Newington, New Hampshire) recently worked on a restoration project of the University of Iowa’s Old Capitol building dome.

The “Old Cap” reportedly once served as the state capitol and is a National Historic Landmark. However, in 2001, a fire destroyed the cupola, dome and bell.

About the Project

Described as “one of the most recognizable images and landmarks in the state of Iowa,” the Old Capitol building was built in 1840. It once served as the state capitol before housing the entire campus of the university.

An accidental fire caused by a contractor using a heat gun during renovations in 2001 destroyed the cupola, dome and bell, requiring four and half years of repairs and renovations before reopening to the public.

Midwest-based firm OPN Architects had first worked on the restoration of the building following the blaze. Then, in 2022, they oversaw the latest restoration and provided guidance throughout the gilding removal and re-gilding process. 

“Working on a historical building with a copper dome meant we had to minimize potential warping of the substrate while still achieving an anchor profile for the gold application,” said Bill Hansen of Allen Blasting and Coating.

“Blasting with sponge media made the most sense for this job. It was gentle enough for use on the substrate, but removed all the existing layers of primer, sizing and gilding on the 550 square feet (50 square meters) dome and left the specified 1 to 2 mil (50 micron) profile.”

According to Sponge-Jet, the Allen Blasting and Coating crew began surface preparation using Silver 120 Sponge Media after the scaffolding and containment was in place.

The company reports that sponge media blasting was selected because of its built-in dust suppression. This was considered especially important on the Old Capitol, as there was reportedly a lead layer below the existing primer, sizing and gilding.

“We were able to minimize the exposure to any airborne lead during the process,” said Hansen.

The sponge media blasting reportedly took 17 hours, with a production rate of 0.5 square feet per minute. The project, which began in the summer, was completed on schedule for Evergreen Architectural Arts to apply the primer, intermediate coating, sizing and roll out the sheets of gold leaf.

“Once we rolled and brushed on the primer, we applied a gold size which is the layer on to which the sheets of gold leaf are pressed into. The size is essentially a slow drying varnish. When it’s dry to tack—about 12 hours—we lay down the sheets of gold leaf,” explained Terry Vanderwell of Evergreene.

Additionally, the museum within the building was open to the public throughout the project. Because of this, crews only had about 200 square feet to stage equipment.

Hansen said that this included the blasting system, which was one blast unit or Feed Unit and one Sponge Media Recycler. Sponge-Jet noted that crews were working nearly 100 feet in the air on scaffolding that was erected around the dome, safety was the top priority, including fall protection with full body harnesses.

“We believed that Sponge-Jet’s Sponge Media was the best choice for this historical restoration job. And I have to say, being a part of something as iconic as the gold dome of the Old Capitol, the center of the University of Iowa, was very special to me,” said Hansen.

“I had to swallow my (Univeristy of Northern Iowa) Panther Pride, but having witnessed the fire that originally destroyed the dome, I was excited and humbled to be able to provide a service to the architect, contractor, and the university to help preserve the iconic symbol that not only represents the university, but also the history of the great state of Iowa,” said Sponge-Jet’s Iowa-based Regional Manager, Cliff Mohling.

Other Recent Restoration Project

In December, Sponge-Jet reported that it played a role in a $300 million historical preservation and renovation project at the New Jersey State House. According to reports, work on the project involved restoring the structure’s gold dome, which called for surface preparation, new coatings and the application of gold leaf.

G.C. Zarnas & Co Inc. (Bethlehem, Pennsylvania) was tasked with the restoration of the 160-foot-tall (from floor to apex) cast iron dome structure at the New Jersey State House.

“Our scope of work was to remove all existing coatings on the substrate down to bare metal and install a new coating system,” said an unnamed project manager and estimator for G.C. Zarnas & Co Inc. In addition to the removal of the old and failing coating, the contractor was also tasked with the removal of all corrosion and oils, soluble salts and other environmental contaminants from the substrate.

According to reports, because the historic preservation and restoration project would take place at heights and over a busy downtown area, traditional abrasive blasting was not an option for the contractor.

In its report, Sponge-Jet shared that, unlike traditional abrasive media, sponge media is reusable, allowing for a significant reduction in media consumption and disposal. In addition, the reduced weight was critical for contractors working on scaffolding for the State House project.

According to the contractor, the biggest challenge on the job was staging the equipment. Members of the team also noted that this challenge would have been much more difficult if traditional abrasive media was used instead of sponge media. 

Once the surface prep was complete, the crew applied a new coating system supplied by Tnemec. The system consisted of four coats: a zinc-rich primer, epoxy patching of small dents and dings to the metal, an intermediate protective coat and a fluoropolymer topcoat.

In the final stages of the project, restoration experts and winners of the 2021 Elevation Awards, Evergreene Architectural Arts applied gold leaf to the exterior section of the structure.


Tagged categories: Blasting; Colleges and Universities; Completed projects; EverGreene; Historic Preservation; Historic Structures; Maintenance + Renovation; NA; North America; Program/Project Management; Projects - Commercial; Renovation; Restoration; Restoration; Sponge blasting; Sponge-Jet; Surface preparation; Surface Preparation - Commercial

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