Bridge Painting Robot: From Forth Bridge to ABB Arms

Steel bridges rust unless their paint is kept up, and for more than a century that has meant crews with brushes and blast hoses working high above water and traffic. A bridge painting robot is meant to take the worst of that work off people, stripping old paint and rust with grit and spraying new coats in places a painter could only reach from a rope or a lift. This post follows the job from the Forth and Sydney Harbour bridges to the blasting robots Rosie and Sandy and a drone that paints over graffiti, then looks at where ABB's arms could fit.

Early morning view of the Sydney Harbour Bridge from the southeast, with Hickson Road Reserve at left, 2017. Photo: Bahnfrend / Wikimedia Commons (CC BY-SA 4.0)

How crews kept the Forth and Sydney bridges painted

The Forth Bridge in Scotland was completed in 1890. Its steel was prepared and painted with boiled linseed oil in a yard at South Queensferry. "Painting the Forth Bridge" became a phrase for a job that never ends. The story that painters started again as soon as they finished was never true, but the bridge did keep a permanent maintenance crew. The Sydney Harbour Bridge, opened on 19 March 1932, has 485,000 square metres of steel to paint, and each coat takes about 30,000 litres. Its painters use a fast-drying paint so drops dry before they reach the cars, and the comedian Paul Hogan once worked among them.

Painters on the central arch of the Sydney Harbour Bridge, 1932. Photo: Powerhouse Museum via Wikimedia Commons (public domain)

Old paint and rust have to come off first. Benjamin Chew Tilghman patented abrasive blasting on 18 October 1870, and Thomas Wesley Pangborn added compressed air in 1904. When Balfour Beatty started a £130 million contract in 2002 to repaint the Forth Bridge fully for the first time, the bridge was wrapped in a climate controlled membrane and every old layer was blasted off with copper slag fired at up to 320 km/h. Then 240,000 litres of a three-coat system based on North Sea oil industry coatings went onto 255,000 square metres of steel. It was designed to last 25 years, and the bridge no longer needed regular painters.

Riveted steel of the Forth Bridge behind scaffolding, blasted and ready for paint, August 2007. Photo: Neil Armstrong / Wikimedia Commons (CC BY-SA 2.0)

Blasting is dangerous because many old bridges carry lead paint, and blasting it fills the air with lead particles. In 2003 Sydney's roads authority began repainting the southern approach spans from platforms below the deck, collecting the lead waste for disposal. Inside those spans the steel vibrates with traffic and the geometry is complex, so the agency asked the University of Technology Sydney whether a machine could do the job. Professor Dikai Liu's team built prototypes with the agency from 2006, and since 2013 two 25 kg robots nicknamed Rosie and Sandy have blasted there. Each one maps its surroundings in 3D and works out where to aim its nozzle, then starts when an operator presses the blast button.

The southern approach spans of the Sydney Harbour Bridge from George Street North, July 1927. Photo: State Records NSW via Wikimedia Commons (no known copyright restrictions)

Crews, drones and spin-offs on today's bridges

UTS describes Rosie and Sandy as the first machines of their kind. With money from Burwell, a Sydney maker of abrasive blasting equipment, the researchers formed a spin-off, Sabre Autonomous Solutions, to adapt the robots for the wider blasting industry. By the university's count there are 270,000 steel bridges in the US, Europe and Japan. Crew work takes time. Chattanooga's Walnut Street Bridge, one of the world's longest pedestrian bridges, reopened on 3 October 2026 after an 18-month restoration. Its fresh blue paint was the most visible change, though crews also replaced the decking and installed new post-tensioning cables.

The Walnut Street Bridge over the Tennessee River in Chattanooga, 2013. Photo: Stephen Matthew Milligan / Wikimedia Commons (CC BY-SA 3.0)

Some of the new painting robots fly. Lucid Bots of Charlotte, North Carolina, makes the Sherpa, a drone that washes building exteriors up to 150 feet high. On 8 October DRONELIFE reported that a local highway system in North Carolina uses its Shield Payload, which sprays coatings, to paint over graffiti on highway bridges. A painting payload is in late development, and one customer has already painted a large new warehouse with it. Heavier work still happens by hand. On 17 October a photographer in Moscow caught a worker in a full blasting suit sandblasting the piers of the Krasnokholmsky Bridge from a lift on a barge.

A worker in a blasting suit sandblasts a pier of the Krasnokholmsky Bridge in Moscow from a lift on a barge, October 2026. Photo: Retired electrician / Wikimedia Commons (CC0)

ABB has no bridge painting robot, but its arms already do the blasting half of the job in factories. At Guyson in Skipton, England, an ABB Foundry Plus robot holds a boron carbide nozzle inside a blast cabinet and keeps the angle, speed and distance to the part steady, a cell described in our post on robotic shot peening and blasting. Foundry Plus arms are sealed to IP67 and finished in two-component epoxy paint, so grit and water stay out. A cell like that could prepare steel parts for a bridge before they are coated. Nobody has announced such a project, and taking the arm onto a vibrating bridge would be much harder than working in a cabinet.

An ABB robot between the open halves of a die casting die. ABB builds protected Foundry versions of its robots for wet, dirty cells. Photo: ABB

Painting is the other half. ABB builds its IRB 5500 robots for car paint shops, and with the PixelPaint head they print a design through 1,000 nozzles without masking. In 2022 they reproduced two artists' designs on cars in less than 30 minutes. Bridge coatings go on in several plain layers, yet the robot's task is the same: hold a spray head at the right distance and angle over a large surface. If a fabricator coated new bridge girders in a shop, a paint robot like this could do it, with the paths checked in RobotStudio first, although ABB has announced no such project.

An ABB IRB 5500 paint robot with its PixelPaint print head over a car body, 2022. Photo: ABB

Where bridge painting robots go next

Longer-lasting coatings are on the way. On 20 October Graphene-Info reported that a graphene-based anti-corrosion coating from a Chinese Academy of Sciences institute in Ningbo has been applied at scale on the 8.28 km Xiangshan Port cross-sea railway bridge in Zhejiang, and its developer says it doubles the service life of conventional coatings. In September researchers at the University of Queensland's AIBN described a self-repairing coating that restricted corrosion to about 37 nanometres a year in electrochemical tests, which they say is 600 times better than many high-performance products. That could make repaints rarer, but each one would still need careful blasting and coating, the work Rosie and Sandy were built for.

The Forth Bridge in July 2015, a few years after its long-life repaint was finished. Photo: PAUL FARMER / Wikimedia Commons (CC BY-SA 2.0)

For factories, Liu says the bridge robot technology can be adapted to steel fabrication, construction and cleaning, so the same machines may end up preparing steel in shops long before it reaches a bridge. For homes, the flying painters are the nearer change. A drone that already washes building walls and has painted a warehouse could plausibly move on to the outside of a house. That is my guess; Lucid Bots has announced nothing of the kind. Painting inside a house is a different problem, covered in our post on paint robots from car booths to home walls.

Advait Kolarkar watches an ABB IRB 5500 robot paint his design onto a car with PixelPaint, 2022. Photo: ABB

Money is the first hurdle. The Forth Bridge repaint was a £130 million contract, and Brisbane's Story Bridge, open since 1935, faces a full restoration that an independent committee said would cost more than the city council can pay. Safety cuts both ways: Sydney built its robots to keep workers away from lead paint and asbestos, but any machine working over traffic brings risks of its own. People stay in the loop as well. Someone has to plan the work and check the steel, and on Sydney's robots a person still presses the blast button.

The Story Bridge and Brisbane's city centre from New Farm, 2013. Photo: Lachlan Fearnley / Wikimedia Commons (CC BY-SA 3.0)

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