A natural oil used for hundreds of years by blacksmiths to protect swords and other metalwork from corrosion could replace toxic paints when maintaining historic metal bridges, a new study has found.
The research, which was published this month in the ICE’s Engineering History and Heritage journal was carried out by engineers Dave Gent and Max Woof on four of our wrought iron bridges and viaducts, which are part of the current or planned National Cycle Network. The 16,575 mile network includes over 800 bridges and structures, many of which are metallic.
The engineers applied a single coat of linseed oil to the structures and monitored them over a 12-month period. Dave and Max also placed a number of small coin-sized samples of the metallic bridges in an accelerated climate chamber in which heated salt water was sprayed regularly on the metal discs to mimic weathering over a number of years. They coated the coins with one, two or three layers of linseed oil to investigate if repeated painting improved the longevity of the protection.
When the pair returned to the bridges a year later they found the linseed oil was still present, helping to prevent corrosion of the structure, while in most cases the oil also rejuvenated existing historic paint protection systems. In the ‘accelerated testing’ the uncoated coins showed greater deterioration compared to the coins painted with linseed oil.
Dave Gent, Chief Engineer at Bridgeway Consulting said:
“Although we do need to do more testing, this early study shows that linseed oil has great potential as a relatively cheap, environmentally-friendly alternative to the chemical-based paints that are generally used to maintain metal bridges.
“It is non-toxic and requires no cleaning of the metalwork before application, so the oil could be easily applied by most people and at most locations.”
Paul Thomas, our Asset Manager said:
“We own many old metal bridges throughout the National Cycle Network and maintenance is a constant challenge, both in terms of staff resources and funding. This traditional method of metal protection doesn’t pollute the environment and could help save us money for other maintenance projects. As it requires no special skills it could even be carried out by our volunteers.”
Our engineers now plan to use linseed oil for future maintenance work and the team will help promote the eco-alternative to other bridge owners and conservation groups around the UK.