The Building Conservation Directory 2020

PROFESSIONAL SERVICES 1 31 C AT H E D R A L C O MM U N I C AT I O N S 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 is suggests this will be a good solution for many situations but there is (presently) only one supplier and single source procurement rarely achieves good value. From a health/ safety perspective it carries similar risks to ribbon anodes, since installation usually by chasing in shallow channels which are then filled with the mortar. Considering the number and variety of anodes available, and that most have been shown to be effective in the right situation, the owner should be wary of advice from the supplier of only one type or brand of anode. They may claim it will solve every problem but there may be a better, cheaper solution out there. TYPES OF STRUCTURE Schemes have been successfully developed for steel-framed buildings with a wide variety of cladding, including sandstone, limestone, glazed terracotta, render and brickwork. The metalwork protected has included embedded columns, beams, support angles, cantilevered beams and cornices/hangers. Late 19th- and early 20th-century terracotta structures are particularly vulnerable to steel frame corrosion because the light breeze concrete used to fill the hollow pots was rich in soluble salts, so water which finds its way in is rich in electrolytes, encouraging corrosion. One of the first to be protected was the London Underground station at Gloucester Road (figure 1). This is a red glazed terracotta tile facade, typical of railway architecture of that era. And many other glazed terracotta facades have been treated with CP, including the Boots Building in Nottingham (figure 4). This building has a series of iron and steel beams and columns protected using a combination of discrete rod anodes and ribbon. The system was installed from both the inside face and external masonry joints, to maximise the access and effectiveness. WHO SHOULD BE DOING WHAT? The owner should carefully consider who they get to design and/or install a CP system. Fortunately, there are qualifications to indicate who is, or is not, qualified for any given activity within a CP project. BS EN ISO 15257:2017 clearly defines these qualifications and, in the UK, there is a compliant training and certification scheme run by the Institute of Corrosion. The certification scheme has four sectors which can loosely be summarised as marine structures, buried structures, reinforced concrete, and the internal surfaces of tanks. The reader will notice that there is no category for ‘early 20th century masonry- clad steel-framed buildings’. It is generally accepted that the reinforced concrete category is broadly applicable. However, while the general principles and products are similar, designing and installing CP to fight Regent Street Disease requires a detailed understanding of the materials and construction type, as well as a sophisticated approach to heritage and design coordination. Someone who is an expert in protecting 1960s concrete bridges is unlikely to have the required experience to tackle an early steel- framed building without assistance. Using a contractor who has installed a similar system, on a similar type of building, can often save much time, hassle and money. LONG TERM PERFORMANCE AND MAINTENANCE All CP systems require monitoring to some extent. The nature and frequency of the monitoring will be dependent on several things: • criticality of the structure • the historic significance of the materials • type of control equipment • location of the structure • likely seasonal variations in moisture and sunlight. BS EN ISO 12696:2016 gives clear guidance on what monitoring is required and when. As this is a standard, it is the baseline in the absence of any other consideration. A more sophisticated discussion of monitoring is presented in the Corrosion Prevention Association’s Technical Note 17. The summary is that the designer should specify the Fig 4. A detail of the Boots Building (now Zara) which opened on Nottingham’s High Street in 1905: its terracotta clad steel frame is now protected by a combination of rod and ribbon anodes