Refurbishing a Jewel: How to Paint the Mackinac Bridge
By Kristi Kates | Aug. 26, 2017
If you think painting your fence is a tough summer project, imagine repainting the entire Mackinac Bridge.
The suspension bridge, which connects Michigan’s Upper and Lower Peninsulas, stretches nearly 5 miles, across the Straits of Mackinac.
“Every component of the bridge has an expected life cycle in the case of its paint,” said Bob Sweeney, CEO and executive secretary of the Mackinac Bridge Authority. “Each new full paint job will have a 35-year life expectancy — but to get that we have continually reapply some of the paint every 3 to 5 years.”
The smaller jobs are regularly completed by the Bridge Authority’s in-house painting team; its crew is monitoring the bridge all the time, watching for small flaws in the paint, so that the team can touch them up before they become major blemishes. “We have to keep an eye on where rust spots start to form, or where bubbles are surfacing in the paint,” said Sweeney. (The photo above shows some rust surfacing on the underside of the bridge.)
The Bridge Authority’s own painting team handles the day-to-day touchups, but the full repainting effort, which involves sandblasting off the old paint and repainting essentially from scratch, is contracted to large teams who specialize in the task.
“We usually get around a dozen bids to contract on our [full] bridge painting jobs,” Sweeney said, “and we require that they come and actually see our bridge firsthand before making their bid. We then take the lowest bid offered, but they’re all good companies — these are guys who are repainting bridges all around the world.”
The current cycle for the full repaint started in 1998, with the bridge divided into seven sections of repainting. Each section is stripped by high-pressure sandblasters right down to the metal and then repainted one section at a time.
“We picked the worst section first, the part with the most rust, which in this case was the south approach to the bridge,” Sweeney said. “Next, we worked on part of the suspended section, then the center span, the north side span, and the north approach. It continues in that way as we skip back and forth across the bridge, working from the worst to the best sections.”
The methodical approach serves a vital purpose: When the team reaches the bare metal, the authority gets an up-close look at the condition of the bridge’s components.
“We do have some fatigue on the bridge at times, so it helps when we get down to the metal, as we can see any small cracks and fix them,” Sweeney said. If this sounds scary, be assured that it’s not: “The cracks are something we expect on any typical steel-structure bridge that’s 60 years old,” he said.
The hazards for the painting crew are as you might expect for anyone working on a bridge: wind, heights, and potentially dangerous equipment. All workers are clipped into harnessed any time they have to work in a hazardous location, and they’re used to the conditions regardless; these guys are pros. Durring the current repainting project, only two have sustained any serious injurie, said Sweeney. “Mostly, we’ve been fortunate.”
If you drive across the bridge as repainting is underway, you might spot painters working inside a tented platform structure, made of canvas and roofing steel, that’s attached to the bridge. It not only offers them a safe, sheltered platform but also prevents the majority of paint chips from blowing out, keeping debris out of the water and in one spot so it can be collected with an industrial vacuum and sent to the appropriate landfill.
“We contain the work as the old paint is sandblasted off because the old paint has red lead in it from back in the day,” Sweeney said. “At the time, the lead was considered a rust preventative, but we stopped using lead-based paints in the late ’80s or early ’90s, and we now use a zinc-based paint.”
GREEN AND WHITE
The distinctive green of the lower part of the Mackinac Bridge is a paint color called Foliage Green Federal Standard 595b Color No. 14110. The white towers are painted in Ivory Federal Standard 595b Color No. 13711. They’re industry-standard colors of an extremely durable paint that are part of a three-layer process that includes a primer coat, intermediate coat, and a urethane final coat. “It doesn’t really ever fade,” Sweeney said.
As for the paint numbers, they’re staggering: The Bridge Authority’s in-house painting crew uses between 1,000 and 1,200 gallons of paint per year for those touch-ups. And repainting the entire bridge takes 135,783 gallons of paint — 128,503 green and 7,280 ivory.
For more information on the Mackinac Bridge, visit mackinacbridge.org, where you can also view the Bridge Cam, which offers glimpses of the painting crews at work.