In the first half of the nineteenth century, typical construction of city centre buildings involved steel framed structures closely clad with stone, brick or terracotta with no gap between the frame and cladding materials. Many of these materials were often porous so over time and out of sight, water ingress caused the steel frames to corrode. By the time it becomes visible the problem is already well advanced.
The 1930s Building Act required building frames to be treated with some corrosion protection but this was often inadequate, ineffective or short-lived. Post 1950s, construction required a cavity between the frame and masonry, allowing for some movement of the frame without dislodging the external facade. It is primarily buildings from before this period that are of concern. Evidence of what came to be known as Regent Street Disease (RSD) began to emerge in the 1970s in London.
Rust grows on the surface of steel frames and this ‘expansion’ gradually pushes against the building fabric causing cracking. Eventually this displacement can dislodge the external stonework, making the building dangerous. Investigation and treatment is highly specialised. It can be expensive, problematic and disruptive as the frame is embedded in the external stonework. At the same time, remediation needs to be discrete and sympathetic to the building. It can be very difficult to eliminate, so preventative measures and a planned maintenance programme is necessary.
John Day, Director of Building Consultancy at Cooke & Arkwright said, “For many years the only remedial method was to remove the external stonework to expose parts of the steel frame and use sand blast or needle gun cleaning methods prior to reinstating the original or new stone. This is both lengthy and disruptive, albeit it provides the opportunity for a visual assessment of the steelwork. It can be difficult to access all the steel so there is always the residual risk of unseen corrosion which can continue to progress.
“A more modern method has been developed using Cathode Protection. This involves the installation of an electrical system which applies a DC current to reverse the direction of the current between the environment and the frame from a positive, rust-forming flow to a negative flow. This will arrest the formation of rust although it does not reverse previous corrosion.
“There are also 3D laser scanning and monitoring processes which can map the building over time and show if any movement has occurred, highlighting potential ongoing problems.
“These require very specialist skills including expert knowledge of historic material and construction methods.
“There are buildings in Cardiff city centre which are of that period and we would highly recommend owners of any such property to consider a specialist survey. As with humans, the earlier you catch the disease the better the chance of a cure.“