When the dome of the Old Capitol building began showing wear and tear from exposure to the extreme Midwest weather, it was critical that the existing gold leaf be removed and replaced without damaging the copper substrate.
Built in 1840, “Old Cap” stands in the heart of the University of Iowa and once served as the state capitol, then housed the entire campus of the university. As UI grew, it remained a focal point of the campus. During the 1970s, a massive renovation took place, and most of the building was restored to its original condition. In 1976, it opened as a National Historic Landmark and museum. "The Old Capitol" remains one of the most recognizable images and landmarks in the state of Iowa," as noted by the University of Iowa website.
OPN Architects, a Midwest based firm with offices in Iowa City that look out to the iconic Old Capitol, first worked on the restoration of the building following a fire in 2001. OPN oversaw the 2022 restoration and provided stewardship 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 550ft2 (50m2) dome and left the specified 1 to 2 mil (50 micron) profile,” continued Hansen.
Once the scaffolding and full containment was in place, the Allen Blasting and Coating crew began the surface prep process using Silver 120 Sponge Media™. One of the biggest advantages to sponge media blasting is the built-in dust suppression. This was especially important on the Old Capitol, as there was 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. Compared to ordinary abrasives, sponge media is recyclable, allowing for cost savings - both when it came to media consumption and the labor necessary for collection and disposal.
The project began in the summer and was completed well before the university’s more than 33,300 students returned to campus. The sponge media blasting was effective and efficient, taking 17 hours, with a production rate of .5ft2 per minute (2.4m2 per hour). This allowed the project to remain on schedule for Evergreene Architectural Arts to apply the primer, intermediate coating, sizing and then 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.
Throughout the job, the Old Capitol Museum was open to the public. “With visitors and staff coming and going daily, we only had about 300ft2 (2m2) to stage equipment,” said Hansen. This included the blasting system (one blast unit or Feed Unit and one Sponge Media Recycler). In addition, the crews were working nearly 100 feet (27 to 30 meters) in the air on scaffolding that was erected around the dome. Safety was the top priority, with all crew members using fall protection with full body harnesses throughout the entire project.
“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 proudly.
Sponge-Jet’s Iowa-based Regional Manager, Cliff Mohling laughed when he said, "I had to swallow my UNI 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."