The Building Conservation Directory 2020

32 T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 0 C AT H E D R A L C O MM U N I C AT I O N S monitoring requirements, and these should be minimised as far as can be justified. In some cases problems arise because well- meaning owners have only partially monitored the CP systems, have used unqualified people, or have misplaced the annual reports. Although this has sometimes led to physical damage to the system/structure, problems are more likely to arise when the building is sold or leased and the new owners ask for the monitoring records. If these are inadequate or incomplete, the purchaser’s representatives have, in recent times, started to ask why and to demand compensation. On a more practical and positive note, the major reason to monitor the CP system is so that the owner knows the structure is protected, that the system’s life is being maximised, that any faults are identified, and maintenance can be planned well in advance. Many buildings were treated with CP in the late 1990s and early 2000s. They are now reaching the stage where first major maintenance is required. In some cases, the DOS and floppy-disk based control equipment is beyond economic repair, or the reference electrodes have reached the end of their service life. In recent years several buildings have had programs of work which have included an overhaul of the CP system. This has ranged from a few thousand pounds of work to back-up the aging IT of the controllers and re-pointing a few metres of anode, through to large contracts to refurbish the system and extend its service life by several decades. Orient House, in the Sackville area of Manchester, was successfully protected in the early 2000s using ribbon anodes placed in the masonry joints (Figures 5 & 6). However, by 2017 the CP system was in need of upgrading and the new owner saw the opportunity to also renovate the CP system, for a manageable cost, while carrying out a programme of facade cleaning, window repair and water- proofing. Most of the system was intact and, with the provision of new monitoring sensors and modern control equipment, the system was effectively re-commissioned in 2017 to maintain ongoing protection. To conclude, Regent Street Disease affects a variety of buildings throughout the world and is particularly prevalent in the city centres of the UK. So long as the condition is properly diagnosed, it can be treated effectively. CP is one option but not the only one, and it may be possible to control corrosion simply by preventing moisture ingress. Each circumstance should be carefully considered. If CP is the correct solution, a variety of anodes, products and approaches are available to the designer to suit the circumstances. All systems need to be monitored and maintained and, if done properly, this can limit the life-time cost of a building with Regent Street Disease. It is likely that there is a case study for every type of early 20th century structure and this experience can be used to determine which system, approach and products are correct for any given circumstance. Further reading The Corrosion Prevention Association publishes a useful series of technical notes, including Technical Note 7, Cathodic Protection of Early Steel-Framed Buildings (Peter Gibbs, 2016) – see www. corrosionprevention.org.uk/publications/. Articles by Chris Wozencroft can also be found on his website at www. corrosionengineering.co.uk/knowledge- library/. See also: Chess, Paul M & Broomfield, John P [2014]. Cathodic Protection of Steel in Concrete & Masonry. CRC Press Taylor & Francis Group: USA. ISBN 978-0-415-39503-8 Clarke, Jonathan [ 2014]. Early Structural Steel in London. English Heritage: Swindon, England. ISBN 978-1-84802-103-7 Historic Scotland Technical Advice Note 20 CHRIS WOZENCROFT is a chartered civil engineer specialising in forensic investigation – see www.corrosionengineering.co.uk. He has extensive expertise in the diagnosis and treatment of Regent Street Disease and corrosion issues in civil engineering structures, and he is a former chairman of the Corrosion Prevention Association. Fig 5. Orient House, Manchester Fig 6. A close-up of the ribbon anode being installed into the masonry joints (Photo: Chris Wozencroft)