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Golden Gate Painting Off to Slow Start

Friday, August 26, 2011

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After months of scaffolding and containment construction, painting is finally underway—sort of—on the Golden Gate Bridge.

The four-year project, which began in May, marks the first complete repaint job ever for the two main suspension cables of the storied bridge, which opened in 1937.

Crews expect to use 10,000 gallons of the bridge’s iconic “International Orange” paint each year coating the outer layer of the cables, after the Navy lost its bid for high-visibility black paint with yellow stripes.

24,500 Tons of Cable

Just over three feet in diameter, each main cable is comprised of 27,572 individual galvanized steel wires—80,000 miles of wire in all—bundled into 61 larger strands and wrapped inside a casing that is then painted for protection.

The 24,500 tons of cable stretch for 1.7 miles over the bridge’s two towers, serving as hangers for the vertical suspender ropes that hold the roadway 220 feet above the bay.

 Golden Gate Bridge

 Rich Niewiroski Jr.

The two main bridge cables top the 746-foot-tall towers and are 7,650 feet long.

The bridge district’s own paint crews are doing the work after pricing an outside contractor at about $30 million. (The first paint job, in the 1930s, cost $112,431.84.)

Scaffolding construction began in February, followed by construction of the containment system.

‘You Really Can’t Paint in this Weather’

Unfortunately, fog and rain have been playing havoc with the painting schedule.

“We are putting a whole coating system on the main cables,” Rocky Dellarocca, paint supervisor, told the Marin Independent Journal as foghorns sounded. “This weather out here right now, with the fog, you really can’t paint in this weather.”

“We haven’t been able to put a coat down in 14 days,” bridge painter Ronald Chatham told the paper Wednesday, standing midspan in a moist wind. “It’s been too wet, and it won’t stick.”

The thick fog shrouding the structure—with towers that rise 500 feet above the busy six-lane roadway—hasn’t made the already-dangerous job any easier.

“You sort of work in slow motion up here with the heights,” Dellarocca told the Journal. “You respect the heights.”

Prep Work Continues

While awaiting better weather, the crews of eight and 10 painters keep busy. The cables must be washed to remove the mildew, salt and residue, and tools used to carefully remove the old coatings without damaging the interior wires. The surface is then sanded, to ensure good coating adhesion, and two coats of elastic paint applied, the newspaper reports.

“The whole bridge moves, so the paint has to move,” Dellarocca said. “A suspension bridge has to be able to move.”

In fact, thermal expansion causes the Golden Bridge to rise and fall up to about 16 inches, sagging in the heat and rising as the cables contract in cooler temperatures.

Bridge officials declined a request to provide more details on the project.

Cable Construction

The main cables were constructed in 1935 and 1936.

First, workers built work platforms that hung under the area where the main cables would be spun. The wire was then laid and a loom-type shuttle moved back and forth, spinning the cables over six months and nine days.

The cable stringing operation was accomplished using four spinning carriages, two working from each anchorage. As one carriage left its anchorage base and went up and over the main tower, then down to midspan, it was then met by another carriage bringing the wire from the opposite anchorage. The wire bights were exchanged, and each carriage returned to its starting point.

Compacting machines were used to “squeeze” the cables into their circular shape. Each consisted of a frame that surrounded the cable with 12 hydraulic jacks around the circle.

Painting History

The bridge was painted when it was originally built with a red lead primer and a lead-based topcoat.  For the next 27 years, only touch-up was required.

By 1968, advancing corrosion sparked a program to remove the original paint and replace it with an inorganic zinc silicate primer and vinyl topcoats.  The topcoat was changed to acrylic emulsion in 1990 to meet air quality requirements.  The original program was completed in 1995 with continuous touch-up on areas with the most severe erosion. 

 Golden Gate Bridge painter

 Goldengatebridge.org

The Golden Gate Bridge, Highway and Transportation District includes 38 painters for bridge maintenance.

“The original coating system has lasted really well, considering how long the bridge has been here,” Dellarocca said. “It has been touched up through the years, but this is the first time the whole thing will be done.”

Dellarocca said most people may not understand the work that goes into their jobs.

“There’s a lot of different variables that affect it. It’s not just the weather,” he told the Journal. “It’s manpower and equipment. There’s a lot of stuff that goes along with it to get the bridge painted.”

   

Tagged categories: Bridges; Containment; Corrosion; Project Management; Scaffolding

Comment from MAHER AL-KHASHRAM, (8/29/2011, 4:54 AM)

consider the rust grip or rust bullet or tarmurust


Comment from Ken Poon, (8/29/2011, 10:49 AM)

I agree with Mr. Al-Khashram's recommendation. As a retire chemist on coating technologies, I prefer Termarust. It chemically reacts with all the rusty components of carbon steel, and effectively displace moisture deep inside the aged cable. Being a flexible coating, it would not crack even at 20 mils, as a barrier to hostile environmental elements.


Comment from peter gibson, (8/29/2011, 11:07 AM)

What coating has been specified for the Golden Gate project. Hostile weather conditions.Would a MC product be suitable ?


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