Leighs Paints’ glass-flake epoxy coating system restored the red luster to the landmark cantilevered Forth Rail Bridge in Scotland. The coating project, completed last December, covered 230,000 m2 and will protect the bridge for a minimum of 25 years. Courtesy of Leighs Paints
A new red coat of paint on Scotland’s Forth Rail Bridge has been applied, finishing a 10- year job. A three-coat system was chosen to restore the luster to the iconic 19th-century railway bridge and protect it for years to come.
February 14, 2012—A special three-coat paint system developed and supplied by Leighs Paints, based in Bolton, England, was applied for the restoration of the landmark cantilevered Forth Rail Bridge in Scotland. The repainting of the 2,500 m long Forth Rail Bridge, completed in December, involved the application of a coating that covered 230,000 m2 at a cost of U.S.$1.4 billion. The Forth Rail Bridge is operated by London-based Network Rail and carries more than 200 trains each day. The principal contractor to Network Rail on the Forth Rail Bridge restoration project was the Edinburgh, Scotland-based engineering firm Balfour Beatty Regional Civil Engineering, a division of London-based Balfour Beatty Group Ltd.
The striking Forth Rail Bridge opened in 1890 as the world’s first significant steel bridge. The bridge spans the fast-flowing waters of the wide Firth of Forth estuary, and stands 110 m from its top to the high-water level. The bridge is subject to the hostile coastal conditions of high salinity, high winds, and sea mists. To repaint the bridge, Network Rail, which led the project from its office in Glasgow, Scotland, chose Leighs Paints’ three-coat paint system because of its anticorrosive and adhesive properties. The coating, a glass-flake epoxy coating system, bonds with the bridge’s steelwork to protect the structure against moisture and oxygen generated by the coastal environment and weather. A total volume of 240,000 liters of paint was used on the project. The coating is expected to protect the bridge for a minimum of 25 years. The process is based on one that the coating company uses on offshore industry structures to help them withstand harsh sea and weather elements.
The bridge spans the wide Firth of Forth estuary and stands
110 m from its top to the high-water level. The bridge is subject
to the hostile coastal conditions of high salinity, high winds, and
sea mists. Courtesy of Leighs Paints
“It is probably the first time in its history the bridge has ever been totally repainted,” says Dave Bottomley, the technical manager for Leighs Paints. “There is a myth in the United Kingdom that painting the Forth Rail Bridge is a never-ending task. It is not true, [although] for many years, there were large areas that were not painted. The old British rail painters could reach only certain parts because access was limited—they were swinging off ropes.”
Balfour Beatty Regional Civil Engineering undertook the restoration work with four principal subcontractors: Gateshead, England-based Pyeroy Ltd., specialists in blasting and coating; the global firm Harsco Infrastructure, specialists in access systems and encapsulation; Aberdeen, Scotland-based RBG Ltd., specialists in steel repairs; and Coventry, England-based ThyssenKrupp Palmers Ltd., which facilitated all three activities. During the 10-year project, more than 1,500 people worked on the structure, with as many as 400 people per day on the bridge at the height of the refurbishment work.
The first step in the paint restoration project commenced in 2002 and involved blasting the old paint, repairing steel, and performing structural maintenance. The team blasted the previous layers of paint from the steelwork, rendering it to a bare silver-grey metal. Workers performed on 4,000 metric tons of scaffolding and in encapsulated, or screened, work areas that prevented debris from affecting or contaminating the surrounding environment. Small sections of steel were replaced, and some of the bridge’s 6.5 million rivets were replaced with nuts and bolts. The architectural lighting system was also refurbished. Walkways were repaired and replaced, and new walkways and catwalks were installed to allow access to the work and to assist in future examinations and maintenance.
Many of the Forth Rail Bridge’s 6.5 million rivets were difficult to
reach and needed to be cleaned and then painted by hand.
Courtesy of Leighs Paints
Following blasting and repairs, the glass-flake coating was applied to the steel in three protective layers by 200 painting contractors using spray equipment, and, in some cases, brushes and pots.
For the first layer, a thin primer was applied to the blast-cleaned steelwork. A black stripe coating was added to the thin primer. For such difficult-to-access areas as sharp edges or corners, the painters used brushes and paint pots to apply the stripe coat by hand and to clean away debris. This was also done for every single rivet head. A high-build primer epoxy—that is, one with a high solids content—was then applied onto the stripe coat. The high-build primer epoxy is made of zinc phosphate, an anticorrosion pigment. This finalized the first layer.
For the second layer, a high-solids glass-flake epoxy that contains a barrier pigment was applied; the barrier pigment is designed to protect the bridge from the elements. “Imagine a flakelike particle,” says Bottomley. “There are lots of these in the film, and they overlap and form a physical barrier, parallel to the substrate, against oxygen and moisture that tries to get through the film to the substrate.” The glass-flake epoxy also contains the zinc phosphate oxide. The glass-flake epoxy was applied with smaller spray tips, and left a smooth finish. “In some areas closer to the water they put two coats of additional protection, down in the spray zone areas, where there is salt water hitting the bridge,” says Bottomley.
Earlier in the process the glass-flake epoxy had been tested because of concerns that a thick film of the substance might not be able to cope with the movement of the structure, especially as trains passed over the bridge, and would crack over time, particularly around rivet heads. Leighs Paints put the epoxy to a severe test. An in-house “flexometer” test used a specially designed rig that strenuously flexed a 90 cm long coated-steel panel. The forces created by these processes both compressed and extended the coating. The test found no evidence of cracking or detachment, and the use of the glass-flake epoxy was approved by Network Rail.
The primer, stripe coat, and an added intermediate coat of red oxide created a color that would complement the bridge’s iconic red finish. The final coat, an acrylic urethane, was then manufactured to the correct red shade and sheen. This coating has gloss retention properties yet is indefinitely recoatable, Bottomley says. “If they need to come back and brighten the structure, they wouldn’t have to start blasting the old paint off,” he explains.
All of the layers, including the primer, passed an accelerated weathering test program at the start of the project before application. The tests included resistance to sulphur dioxide, water immersion, humidity, ultraviolet light, condensation, and 5,000 hours of exposure to salt spray.
Bottomley says that one significant challenge in repainting the bridge was the hostile environment. “Even with encapsulation and good working conditions, we did get strong winds,” he says. “It reached a point where the workers had to vacate the structure. They had three or four days when it was too cold or windy to paint. Some days the humidity was too high to paint. A dehumidifier was put in the encapsulation [work area] to counteract it.”
Additional challenges included reaching the bridge’s angles and sandwiched steel plates. “The bridge was a major project because it was difficult to access,” says Bottomley. Corrosion traps, built into the structure, were found to contain dirt and water, which are potentially aggressive to the new coating, and these had to be cleaned out. But the painting crews did not discover any significant structural issues with the bridge as they completed their work, Bottomley says.
The glass-flake epoxy coating system bonds with the bridge’s
steelwork to protect the structure against moisture and oxygen
from the coastal environment and weather. Courtesy of Leighs
In a press release, Marshall Scott, the managing director of Balfour Beatty Regional Civil Engineering, said, “It is a testament to the skill and commitment of the project team, and the subcontractors and suppliers involved in this significant and complex program of works, that the iconic Forth [Rail] Bridge has been returned to its original condition.”
David Simpson, the route managing director for Network Rail, added, “The completion of this refurbishment will safeguard the future of one of the country’s most famous landmarks. Repainting the bridge has long been considered one of the world’s never-ending tasks, and the refurbishment program we have just completed has been one of the biggest engineering challenges Network Rail has faced.”
Repainting is an unenviable task for any operator of a very long and complex bridge; just as it is often said that the Forth Rail Bridge repainting would never end, it is often said of the Golden Gate Bridge in San Francisco that if one started painting it at one side, by the time the job was completed at the other end, it would be time to start over again. Not so, says Mary Currie, the public affairs director for the Golden Gate Bridge. “We don’t paint the whole bridge from one end to the other,” Currie says. “I don’t think any bridge does. We paint by priority.
“The Golden Gate Bridge is sitting in a marine environment with fog and sea salt,” she explains. “As part of the federal inspections and our own ongoing inspection, every year we create our budget and look at what needs to be painted and what is the next priority.”
Currently the Golden Gate Bridge’s main cable is being painted, with scaffolding at midspan on both sides. “We started last April,” Currie says. “With the rigging, painting, and containment, it will probably take six years.”
Even at the newly-finished Forth Rail Bridge, work continues. Contractors will work through spring to decommission site compounds and restore a public viewing area. Network Rail has stated that a small team of specialists and engineers will continue to monitor and maintain the bridge in the years ahead.
Bottomley says that if he were to pick one bridge in the United Kingdom to paint, the Forth Rail Bridge would be the one. “It is an iconic structure,” he says. “I am proud to be associated with it.”