The corrosion of steel building frames in London is becoming a problem.

This issue is largely reserved for metal buildings built in the first half of the last century. Pre-war architects' and engineers' understanding of the corrosion process was not as comprehensive as it is today. Therefore, it was typical for structures designed and built during that period to have masonry tightly packed around the steel building frame; any voids were generally filled with mortar and/or rubble.

This tight packing around the steel creates a sponge effect, which provides ideal conditions for corrosion to take place.

The corrosion process can take a long time to show any symptoms. However, once it takes hold, it can accelerate rapidly. As steel corrodes, it increases in size, by up to eight times its original volume. Without space around the steel building, this growth exerts significant pressure on the surrounding masonry. Small cracks can quickly worsen and masonry can become a significant risk.

When the disease first emerged in the 1970s, the only option for treatment was to remove the masonry to access the steel frame, treat and/or remove and replace the steel and finally replace the masonry. Clearly this was not only costly, but also highly disruptive to the daily business of a metal building.

The non-disruptive option, known as cathodic protection, was first used on the Royal College of Science, Dublin, in 1991. Dr Holger Garden, customer director at Taylor Woodrow's Technology Centre, explains the technique that helps with this commercial metal building problem:

"In order to reduce the risk of corrosion, the potential (voltage) of the steel needs to be reduced, i.e. made more negative. To achieve this, tubular anodes are strategically positioned in holes drilled around the steel frame. The anodes are then connected together in zones with wires hidden in mortar joints. The zones are powered by local rectifier units, which are controlled by a main computer.

"Post-installation, an internet link enables the team to keep a close watch on the performance of the system and the condition of the steel from the Technology Centre. Settings can then be adjusted as and when required."

Taywood's Dr Mohsen Mazraeh, senior corrosion engineer, and Richard Norwood-Grundy, head of building pathology, have also highlighted a number of examples, the most important being two years ago at the home of the Contract Journal Awards, the Grosvenor House Hotel on London's Park Lane.

The Grosvenor's lower three floors were clad in Portland stone and the upper six in red brick. In recent years, the masonry showed increasing signs of deterioration as a result of the corrosion of the commercial steel building frame within.
The hotel remained open throughout Taywood's work, as a lot of the work was carried out at night. Dr Mazraeh notes there were few complaints.
"The Grosvenor is the largest steel-framed cathodic protection installation in the UK," says Dr Mazraeh. "There are excellent opportunities [for us] off the back of it."