For the last twenty years, the bridge has been protected against corrosion by a combination of special epoxy undercoats and acrylic gloss finish-coats. During the refurbishment works, we’ll be using the same kind of epoxy and acrylic urethane coating system on the visible parts of the suspension chains, plus a bitumen-based coating system on the chains and saddles in the tops of the towers and underground in the anchorages. A mix of silicone, aluminium and zinc-based products will be used along the sides of the bridge to coat the lattice straps, stanchions and parapet girders. The paints are all lead-free, compatible with the many layers of previous paints, and can be applied even in temperatures as low as 0 degrees Celsius.
Before the paint can be applied, the ironwork will be washed with detergent & water, and any loose paint carefully removed through a process of scraping and abrading using a combination of power tools and hand tools. The painters will be using a ‘surface tolerant’ primer, meaning that the new paint is ideally suited for application on to older structures where it is not practical to remove all the old paint layers back down to the bare iron.
All of the surface preparation and painting works will be undertaken from temporary platforms which will be fully enclosed with sheeting to prevent any debris, dust or paint spatters escaping into the surrounding environment.
History
The bridge has not always been grey. Early accounts of the bridge describe the chains as being painted chocolate brown and the bolts on the chains were gilded with gold.
However, the principal paint used to stop the bridge rusting was red lead. This was a mixture of red lead, boiled linseed oil, turps and litharge (one of the natural mineral forms of lead oxide). The under cross girders (visible when looking up at the bridge from below) and the anchorages where the chains were anchored underground were covered with bitumen tar. In 1955-56 the cross girders under the carriageway were sand blasted and coated with molten zinc by the Bristol Metal Spraying and Welding Co Ltd.
Maintaining the paintwork was a regular job that was carried out by hand by teams of maintenance men when the weather was fine. To repaint the whole bridge took between 8 to 10 years. Once completed, the cycle would begin again.
From red to silver-grey
A major repainting programme was carried out from 1959 to 1960. At this point the main colour of the bridge changed from dark red to silver grey. Throughout the 1950s, the city architect, Mr J. Nelson Meredith campaigned for the repainting of Bristol’s built environment and promoted the repainting of the bridge to a light grey which he considered to be ‘a bright, clean, cheerful yet restful colour.’ As well as reflecting a change in taste, the new paint system was also more durable and offered a more reflective surface for lighting up the bridge.
After this re-painting programme, the lifecycle for re-painting doubled to approximately 20 years, with different parts of the bridge being painted at different times within the cycle and other parts ‘patched-up’ when needed. The bridge’s wrought ironwork has been through two 20-year major repaint cycles since the 1960s and is now due for its third.
Painting underground
As well as painting the chains high above the river, the painting team will also need to make their way into narrow underground inclined tunnels to clean and repaint the parts of the chains that are below ground level. These chains have been protected with bitumen paints since the bridge was constructed almost 160-years ago! Many modern paints are not compatible with old bitumen coatings and therefore bitumen paint continues to be applied successfully for the protection of the ironwork below ground.
