Repairs to Chester’s historic Watergate Bridge have revealed an unorthodox repair technique used by 19th century stonemasons.
While the discovery is a fascinating one, it will lead to delays to the repair scheme which will now continue until the end of the year.
Cheshire West and Chester Council’s Bridges Team and the specialist stonemasons have been amazed at what has been uncovered as the bridge parapet was dismantled during a comprehensive programme of works to repair the structure.
Instead of a single foundation stone, the parapet is now actually built on two foundation stones - with a cavity in the middle.
This is a technique that some of the most experienced stonemasons working on the site have never seen before and explains why the parapets have been leaning outwards.
The discovery means the repairs will take much longer than previously estimated.
Further investigations have revealed that work on the bridge in the 1920s resulted in the cavity being ‘filled in’ with cement – a new material at that time.
However, the rigidity of the cement has meant that trapped moisture couldn’t escape through the hard mortar and has travelled through the softer stonework instead.
Initially the project estimated that 10% of the stonework on the bridge would need to be replaced due to ‘delamination’ – where water flakes away outer layers of stonework.
However, recent findings now indicate that perhaps up to 90% of the stonework will need to be replaced because the hard cement has bonded so strongly to the stone that it cannot be removed without causing damage to the stone.
The council’s director of place operations, Maria Byrne, said: “Skilled stonemasons working on the repairs are using traditional techniques and materials to restore the bridge to its former glory so that it can be enjoyed for generations to come.
“Our Bridges Team had no idea that this rather strange repair method would be revealed when the Grade I listed bridge was stripped back. The filling in of the cavity with cement in the 1920s has caused moisture to travel through the stonework itself, rather than the mortar – essentially ‘killing off’ the stonework. It’s a much larger repair project than we first thought but the end result will look wonderful.”
The programme of repairs is now expected to finish at the end of the year.