Complex cover-up: firm finally finishes painting the Forth Bridge

There is a British expression “like painting the Forth Bridge” - coined to describe a never-ending job, one that takes so long that when you have finished it, it is time to start again.

But this particular task has finally been completed. Very few people are able to consign a well-established figure of speech from the lexicon of everyday use into the dustbin of history but that’s exactly what has been achieved by the union of Network Rail, Balfour Beatty and a team of some 200 painters.

Thanks to their efforts - and a specialist coating system developed by Leighs Paints - the colloquial expression for a never-ending task, is no more.

The scaffolding and covers have just been removed from the 1.5 mile-long rail bridge, which connects Edinburgh to Fife across Scotland’s Forth Estuary, to reveal its new red coat and the expectation is that at least 20 - and perhaps as many as 40 - years will now pass before the job needs to be done again.

It cost 130 million pounds and took the team 10 years to apply 230,000 square metres of a triple layer of glass-flake epoxy paint, creating an almost impenetrable chemical barrier that should seal and protect the bridge's Victorian steelwork from the weather.

Before they could begin the job, all previous layers of paint had to be blasted from the bridge for the first time in its 120-year history, to allow extensive repairs to be made to its steel.

One of the biggest hazards facing the bridge is its location, an aggressive and sometimes hostile environment incorporating fast flowing coastal waters with moderate to high salinity, high winds and sea mists. The bridge’s structure is exceptionally complex; its 53,000 tonnes of steel includes 6.5 million rivets, back-to-back angles, sandwiched steel plates and corrosion traps.

The piers that support it are faced with two-feet thick granite and comprise 120,000 cubic yards of concrete and masonry.

At the height of its construction, more than 4,000 men were employed and in the seven years it took to build, 57 lost their lives. Its importance cannot be overstated; 150 trains cross its span every day, carrying some three million passengers and eight million tonnes of freight each year.

It has also become something of an icon in and of itself, attracting a significant number of visitors throughout the year. Perhaps, unsurprisingly, given its striking design, it is frequently used as a backdrop in photo-shoots.

Leighs Paints, based at Bolton in north-west England, chose the glass-flake epoxy paint system because it had proven itself in the far harsher environment of North Sea oil rigs. Its effectiveness is due in part to its excellent adhesion and anti-corrosion properties that act as a powerful barrier against the harsh weather conditions.

The selected system consists of a higher build blast primer, an epoxy glass-flake build coat and an acrylic urethane finish, as well as a stripe coat of epoxy glass flake. It was important to maintain the striking red-oxide colour of the Forth rail bridge, and so the team ensured that the primer, stripe and intermediate coats had a sufficient colour contrast, while complementing the traditional Forth rail red finish.

The finish coat is based on an acrylic urethane resin system manufactured to the required gloss level and colour shade; it has very good colour and gloss retention properties and is indefinitely recoatable - advantageous for future repaints because surface preparation can be kept to a minimum.

Dave Bottomley, Leighs Paints technical manager, said: “We are delighted to have played a part in the restoration of such an iconic structure as the Forth rail bridge. The paint system used on the structure has primarily been used in the offshore industry. Its glass-flake epoxy formula bonds with the metal to keep moisture out.”

Engineering group Balfour Beatty had the unenviable task of restoring the structure and started the process in 2002, blasting the 53,000 tonnes of steelwork back to bare metal before applying the tough coating.

David Simpson, route managing director for Network Rail Scotland, added: “Network Rail is the proud steward of our railway history which the Forth Bridge exemplifies. Since 1890 it has been a working monument to the genius of British railway engineering. Over the last decade, the bridge has been restored to its original condition and its new paint will preserve the steelwork for decades to come.”