Howrah bridge is set to be repainted for the first time in eight years, a task as imposing as the 26,500-tonne structure that bears the weight of a lakh vehicles every day.
Calcutta Port Trust (CPT), which maintains the city’s busiest bridge, has already started removing rust from the structure and hopes to complete the painting job within six months.
The biggest challenge for the agency contracted to paint the colossal structure would be to avoid traffic disruption. Since 1943, when the bridge was opened to traffic, it has been the main link between Calcutta and Howrah.
According to experts, the decision to give the bridge’s superstructure and belly a coat of primer and paint has come not a day too soon.
The structure hasn’t been repainted since 2005 and its wait for a fresh coat has stretched around three years beyond the recommended period.
“An internal study last year revealed corrosion in several parts of the bridge’s steel surface because of vehicular pollution and moisture,” a senior official said.
The superstructure and belly would need six coats of paint and primer each to keep them corrosion-free for the next five to six years. That works out to around 25,000 litres of primer and paint!
Metro highlights what it takes to paint Howrah bridge.
How important is it for Howrah bridge to get a coat of paint immediately?
Metallurgy scientists say a steel structure like Howrah bridge requires a fresh coat of paints every five to six years. “The steel structure faces regular corrosion because of moisture from the river and the generally high humidity in this part of the country. Vehicular pollution is also a factor,” an expert said.
A study by Calcutta Port Trust in early 2013 revealed significant wear and tear with rust settling on parts of the structure where the surface paint had peeled off.
What will be the expenditure?
The estimated cost is about Rs 1.5 crore.
What type of paint will be used?
The superstructure is 2,150ft long from one end to the other and 280ft tall from its foundation. After the old paint and rust are removed from the surface, two coats of yellow zinc chromate primer will be applied on the steel work. Yellow zinc chloride is said to have anti-corrosive properties.
“Even if the upper layer of paint peels off, the zinc chloride will provide protection to the main structure,” an expert said.
Two layers of aluminium paint will be used as primer. Aluminium paint functions as a barrier coating that doesn’t allow moisture and water to corrode the steel surface. Aluminium also provides shine and glow.
Two layers of chlorinated rubber-based paint will be used over the primer. It is estimated that around 25,000 litres of paint will be required.
The paints have been procured and sent to a laboratory for tests.
“We will start work as soon as the reports reach us. The contractor has been finalised and the process of removing rust has begun,” a CPT official said.
Will the painted bridge look different from what it is now?
Howrah bridge will retain its existing aluminium shade. Aluminium has been the preferred shade from the time Howrah bridge was opened 71 years ago.
“It glows under the blue lights that line the bridge. After the fresh coat of paint, the bridge will obviously have a shinier look,” an official said.
How many workers will be deployed for the paint job?
A minimum of 100 and a maximum of 150 every day for six months.
Will traffic on the bridge be affected?
No, there won’t be any traffic disruption since the workers will mostly use built-in ladders and harnesses to reach every part of the bridge. The few extra ladders that will be required won’t cause disruption, say officials.