Institute of Historic Building Conservation No 139 May 2015 Working with metal Cathodic protection in church towers Iron frames in textile mills Brunel’s other bridge
C O N T E X T 1 3 9 : M A Y 2 0 1 5 1 Cover: Wrought iron (see page 9) (Photo: Topp & Co) www.ihbc.org.uk Registered as a charity in England andWales number 1061593 and in Scotland number SC041945. Company Limited by Guarantee. Registered in England number 3333780. Registered Office: 3 Stafford Road,TunbridgeWells, Kent TN2 4QZ. Officers President Trefor Thorpe, president@ihbc.org.uk Chair Mike Brown, chair@ihbc.org.uk Vice Chair Emilia McDonald, vchair@ihbc.org.uk Secretary Jo Evans, ihbcsecretary@ihbc.org.uk Treasurer Richard Morrice, treasurer@ihbc.org.uk National Office Director Seán O’Reilly, director@ihbc.org.uk Projects Officer Fiona Newton, projects@ihbc.org.uk Consultant Consultations Coordinator James Caird, consultations@ihbc.org.uk Membership Services Officer Carmen Moran, membershipservices@ihbc.org.uk LETS Officer Kate Kendall, lets@ihbc.org.uk Administration Officer Lydia Porter, admin@ihbc.org.uk Committee Chairs Policy David Kincaid, policy@ihbc.org.uk Membership & Ethics Paul Butler, membership@ihbc.org.uk Finance & Resources Richard Morrice, resources@ihbc.org.uk Education David McDonald, education@ihbc.org.uk Communications & Outreach Charles Strang, communications@ihbc.org.uk Branch Officers North Geoff Underwood, 0191 433 3435 NorthWest Crispin Edwards, 0161 474 2620 Yorkshire David Blackburn, 01943 603479 West Midlands Charles Shapcott, 0121 7044312 East Midlands Roy Lewis, 01623 756623 South Julia Foster, 01296 585888 SouthWest JamesWebb, 01202 732849 East Anglia David Andrews, 07760 208231 South East Sean Rix, 01483 523379 London Sheila Stones, 01223 582716 Scotland Stuart Eydmann, 07525 479835 Wales John Edwards, 07796 440934 Northern Ireland Jill Kerry, 028 9048 7395 Republic of Ireland Cormac O’Sullivan, 00353 5677 62907 Institute ofHistoricBuildingConservation No 139May 2015 Working with metal Cathodic protection in church towers Iron frames in textilemills Brunel’s other bridge 2 Briefing 3 Out of Context 4 Letters 5 Periodically 7 The writer’s voice METAL 9 Editorial 10 Wrought iron, yesterday and today Chris Topp 14 Dredge’s Victoria Bridge Richard Baister 17 Brunel’s other bridge in Bristol Geoff Wallis 20 Cathodic protection in church towers David Farrell 24 Iron frames in textile mills Mark Watson 28 Aspects of copper roofing Jonathan Goode 31 Going underground Justine Page 34 Sweating heritage assets Justin Webber 39 Notes from the chair 40 Director’s cut 41 New members 42 Vox pop 43 Book reviews 47 Products and services 48 Advertisers index
2 C O N T E X T 1 3 9 : M A Y 2 0 1 5 Editor Rob Cowan Editorial Coordinator Fiona Newton, 01507 602567 editorial@ihbc.org.uk Editorial Board Nigel Crowe Peter de Figueiredo (book reviews) Rebecca Madgin Fiona Newton (chair) Elizabeth Smith Michael Taylor Cartoons by Rob Cowan Context is distributed to all members of the Institute of Historic Building Conservation. © Institute of Historic Building Conservation 2015 ISSN 0958-2746 Publisher Cathedral Communications Limited, High Street, Tisbury,Wiltshire, England SP3 6HA 01747 871717 context@cathcomm.co.uk www.buildingconservation.com Non-member subscriptions to Context Context is available to corporate bodies at an annual subscription rate, including postage, of: United Kingdom £60.00 Elsewhere £90.00 The views expressed in Context are not necessarily held by the IHBC or the publisher. Neither the publisher nor the IHBC shall be under any liability whatsoever in respect of contributed articles. We gratefully acknowledge the support of firms whose advertisements appear throughout this publication.While every effort has been made to ensure that the information contained in this issue of Context is current and correct, neither the IHBC nor the publisher can be held responsible for any errors or omissions which may occur. Briefing Context Copy deadlines Context is published five times a year, in March, May, July, September and November. The next four copy deadlines are: September, issue 141 17 July November, issue 142 11 September March, issue 143 15 January May, issue 144 11 March Partners at Sussex Brighton and Hove City Council, the University of Sussex and English Heritage are set to sign up to a listed building heritage partnership agreement. It is likely to be the second such agreement in Britain and the first involving a university. The first listed building heritage partnership agreement in England was signed between English Heritage, Maldon District Council and the trustees of Stow Maries Great War Aerodrome in Essex last year (see Context 138, March 2015, page 2). The University of Sussex was the first of a new wave of universities created in the early 1960s. The early buildings were designed by Sir Basil Spence, and include one Grade I and seven Grade II* listed buildings. They have many common design features, such as flat roofs, red brick and concrete arches. The university claims to have continued to develop the site in sympathy with the early design and site layout. The agreement will mean that listed building consent for general or repeated work would be granted without the need for the university to individually apply for consent – cutting red tape and saving time and money. This includes work to repair or replace the external fabric of buildings, internal fixtures and finishes, upgrading teaching facilities and works to improve safety and accessibility. The agreement would set conditions to ensure that work is carried out consistently using materials in keeping with buildings. A draft listed building heritage partnership agreement was agreed by the council in January and since then has been subject to public consultation. The proposed agreement will run for 10 years, subject to periodic review. Samantha Johnson, inspector of historic buildings and areas for English Heritage in the south east said: ‘Spence’s buildings at Sussex University are an outstanding example of 20th-century architecture. Spence’s inspiration was from the classical forms of ancient Rome. ‘At Sussex, the voids and spaces he created at Falmer House capture the idea of the ruinous condition of the Colosseum. He was also influenced by Le Corbusier’s Maisons Jaoul, which is seen at Sussex in the concrete arches and austere red brickwork across the campus.’ Archiving Insall Conservation architects Donald Insall Associates have handed over significant records from 1960s Chester to Cheshire Archives for safe keeping. Comprising over 5,000 slides and six boxes of files, the documents, drawings and slides were important research for the preparation and presentation of the 1968 Insall Report, a landmark in the history of conservation in the city and of professional conservation Falmer House and its courtyard, inspired by the Colosseum
C O N T E X T 1 3 9 : M A Y 2 0 1 5 3 ‘ESSENTIALLY the architecture is part of the country’s historical fabric, representative and testament to a period of a nation’s history. In terms of interpretation of the past, Germany is widely regarded as a leader in dealing with its darker history. ‘It is evident in German museums and heritage sites of the period that a fastidious approach to documentation and evidence dominates. Built heritage and architecture simply have to be treated in the same way. ‘Interest in the history of the period is well documented and the buildings are part of the historical legacy constituting visitor attractions in many parts of Europe.’ John Lennon of Glasgow Caledonian University introducing a conference exploring opportunities for tourism in Germany to National Socialist architecture, some of which requires conservation. The conference was held at the Peenemünde Historical Technical Museum, which between 1936 and 1945 was a technological facility where slave labourers, concentration camp inmates and prisoners of war built armaments. Sir Donald Insall with Lisa Greenhalgh, senior archivist at Cheshire Archives practice. Cheshire Archives hopes to secure funding to repackage, describe and digitise the slides, making them accessible for researchers. In the 1960s, Chester’s historic centre and its remarkable heritage of historic buildings were still suffering from years of wartime neglect. The loss of archaeological remains such as the baths, still of great size and a high degree of preservation, had also provoked much controversy. By 1966 opinion was changing. The government’s minister of housing and local government commissioned a pilot study of four towns of special historic importance, including Chester, to elicit what special problems such places faced in relation to their modern development. The study led to the formulation of a national policy on conservation. The Insall Report dealt with all aspects of town planning, from traffic management to tree-planting. It recommended that the restoration of old buildings could enhance both their own value and that of the whole city centre. The report provided a realistically costed 15-year programme which identified the buildings most in need of saving. In 1969 a conservation area of 200 acres was declared, including the city within the walls. The council began acquiring, restoring and selling endangered buildings, and encouraged private owners, developers, and architects to undertake similar renovation work. In 1971 Chester appointed what was Britain’s first local authority conservation officer. ‘IT WOULD be a huge pity if we decided that by the time we had reached the 200th anniversary of the vast fire which consumed the old Parliament and brought this one in to being we had to abandon this site and look elsewhere in order to serve the public interest properly. ‘Yet I will tell you in all candour that unless management of the very highest quality and a not inconsequential sum of public money are deployed on this estate over the next 10 years that will be the outcome. ‘This is a fabulous institution located in awesome surroundings. It must not have the ethos of a museum. It will require bold and imaginative managerial leadership to ensure that we are a parliament fit for purpose and that this Victorian legacy can be rendered practical for contemporary representation.’ John Bercow, Speaker of the House of Commons, warning the Hansard Society of the urgency of repairs to the Palace ofWestminster. ‘THE CARLTON Tavern, built in 1920–21 for Charrington and Company, probably by Frank J Potter, was an early inter-war improved public house, carefully detailed and built of good quality materials, showing the vision of a leading London brewery. ‘It was laid out as an improved pub with a public bar, and originally off sales, a saloon, and unusually a luncheon and tea room. The site was remarkably well-preserved externally and internally, it displayed the hierarchy of rooms in their fixtures, fittings and decorative treatment and retained all its external signage. ‘Few pubs were built at this date and fewer survive unaltered. It also had great historical interest as an improved pub, illustrative of growing concern at raising the reputation of public houses, by providing family facilities and reducing drunkenness.’ Historic England expressing regret at the sudden demolition of a pub in Kilburn, London, which it had been considering recommending for listing.
4 C O N T E X T 1 3 9 : M A Y 2 0 1 5 ‘IS UNESCO world heritage status worth the paper it’s printed on? ‘Edinburgh’s role as a quality European destination underpins its economy, bringing in an annual £1.6 billion to its coffers and its architectural heritage plays a huge role in this. That is why I am submitting a report to members of the UN Board of Auditors at UNESCO headquarters in NewYork (assuming they’re prepared to listen) in a bid to persuade them to overturn the city’s world heritage status... ‘Why do the powers-that-be want to trash this treasure?... I don’t simply refer to the local council, which seems minded to sanction developer mediocrity on an alarming scale. There’s also the Scottish government, which has declared an intention to offload the most architecturally significant public building in Scotland – Robert Adam’s General Register House. Its functions, it is claimed, can be transferred to a wasteland at distant Sighthill. ‘Or how about the National Trust for Scotland, which decamped from its neoclassical headquarters in Charlotte Square to another outof-town pale of settlement?... ‘You’d think lessons might have been learned. Not a bit of it. There are plans to raze the last Georgian block between St Andrew Square and General Register House. Nearby, the hope is to reconstruct 1970s St James Centre, once vilified as a looming mass. ‘So what has UNESCO world heritage status done for us? Frankly, it’s been an unmitigated disaster, and we’d have been better off without it.’ David Black, chair of Edinburgh’s Southside Association, writing in the Guardian ‘THIS IS YET another attack against the Iraqi people, reminding us that nothing is safe from the cultural cleansing under way in the country: it targets human lives and minorities, and is marked by the systematic destruction of humanity’s ancient heritage. ‘The deliberate destruction of cultural heritage constitutes a war crime. There is absolutely no political or religious justification for the destruction of humanity’s cultural heritage.’ Irina Bokova, head of UNESCO, telling the BBC of her outrage at the bulldozing of the ancient Assyrian city of Nimrud by Islamic State militants in Iraq. Letters Trinkets and cappuccino From John Fidler, Marina Del Rey, California I enjoyed the focus on changing retail impacts in the latest issue of Context (No 138, March 2015). But what struck me most upon reflection on my home town of Stockport was the slow and painful socio-economic injury caused to historic cores by associated strategic planning decisions. For example, back in the 1960s, the borough council cleaned away Georgian and Victorian ‘slums’ and moved the residents a bus ride away from the town centre. This resulted in empty, unsafe streets at night and fewer punters for basic groceries in the market square. Less than half a mile from the marketplace, a large shopping precinct was built on Church of England land with a lease condition that no alcohol be served in the area. This resulted in no night-time restaurants, and little street life except for vagrants and vandals. In the 1980s, retail boxes were added to the ends of the precinct, along with copious car parking remote from the historic core, resulting in further commercial erosion of the market place and ancillary streets. The retail threat here came from adjacent retail development, not tin sheds out beyond a ring road several miles away. Only now, in the second decade of the 21st century, have local councillors woken up to the issues. These are: • facilitating inner-core housing in both new and sensitively rehabilitated buildings (mostly funded by far-sighted housing associations) • engineering park-and-ride and microbus routes over the steep topography back to the restored marketplace • investing heavily in town scheme projects of repair and enhancement. But is it too little, too late? Look at the photo of the historic Underbank in the heart of the primary conservation area. Notice the large number of For Sale and To Let signs. On a recent return to my roots, I counted at least 30–50 per cent of all property in the inner core to be for sale or lease, or under-utilised on the upper floors and clearly at risk. Worse, the large Victorian market buildings stand comparatively empty, selling hardly any staple meat, cheese or vegetables and only trinkets now – each sadly competing with one another and with adjacent pubs and cafés to sell trendy cappuccino drinks to the odd tourist and occasional passer-by. Locals complain in the Manchester Evening News about increasing levels of crime and a new Market Superintendent who jacked up the stall rentals so much that everybody left for better pitches in nearby Hyde, Ashton and Macclesfield. Shop signage (Context 138, page 23), frankly, is the least of local concerns. John Fidler Stockport’s Underbank: painful injury
C O N T E X T 1 3 9 : M A Y 2 0 1 5 5 Periodically The latest issue of the Institution of Civil Engineers Proceedings on Engineering History and Heritage (Vol 168, issue EH1, February 2015) presents three papers from different research groups concerning robust engineering processes required to answer questions of structural decay caused by increased environmental loading. The papers explore different structural materials and types, and widely different levels of exposure. They explain differing techniques of assessment, ranging from on-site monitoring, to numerical modelling and the microscopic analysis of materials. The first paper, by a team at University College London, involves a traditional timber-framed and brick infill 16th-century building in Tewksbury (a town not unfamiliar with the problems of flooding), and the lessons to be learned from monitoring internal variations in temperature and moisture over a 12-month period. The team used dynamic vapour sorption (DVS) to determine how hygrothermal damage might occur with a resulting loss of strength and physical integrity of the structure. By measuring the temperature and relative humidity at the external surface and within the thickness of the walls, the temperature gradients show that micro-cracking can occur. This leads in turn to the uptake of moisture and water penetration. The conclusion reached is that tests should be undertaken before the installation of dry-lining where the prevention of heat loss is desired, as the insulation material can substantially alter the temperature profile within the wall, increasing both moisture movement and relative humidity, and therefore the risk of fungal attack. The second paper looks at vernacular Scottish mud-wall construction and its vulnerability to water penetration and freeze-thaw cycles. Examples in and around Errol in the Carse of Gowrie were selected, as this represents the greatest regional concentration of such buildings. Two representative case studies demonstrate the typical issues that can be encountered and how the monitoring of each building was undertaken, with reference to climate models, current weather data and the local climatic context. Temperature and humidity data were collected from within the walls for a year from April 2012 (during which the area experienced a range of extreme weather events). The data collection and analysis has enabled some conclusions to be drawn about the potential impact of climate change and the formulation of recommendations on how an integrated approach to the analysis of other historic mud-wall structures can be achieved. The third paper looks at buildings in the much more extreme environment at the Prince of Wales Fort, Manitoba, northern Canada. Originally built to secure the fur trade, the surviving 18th-century masonry walls were partially frozen for much of the year when built, but recent climate change has raised average yearly temperatures. Consequently the pattern of freezethaw cycles has altered significantly, resulting in a breakdown of the mortar within the stonework; washout from melting snow and rain; and lateral deformation of some sections of the walls and collapse of others. Micromodelling techniques were employed to assess the in situ condition of the damaged walls, and establish the general susceptibility of such historic fortifications to failure due to changing environmental conditions that practicing engineers should be aware of. The latest ASCHB Transactions (Vol 37, 2014 [sic]) has six major papers, all of which are of interest and well illustrated in colour. They start with an exposition of the recent repair and refurbishment of Harvey Court, Gonville and Caius College, Cambridge, listed Grade II* in 1993. Matthew Goulcher of Levitt Bernstein describes works that began by addressing pre-existing defects and water leaks, and widened to include modernisation of the student accommodation, and better security and access. Harvey Court is considered to be a seminal late 20th-century collegiate building, noticeably influenced by the work of Alvar Alto. When designed by Sir Leslie Martin and Colin St John Wilson in 1960–62, the building form reinvented the traditional Oxbridge transactions volume 37 for 2014 ASSOCIATION FOR STUDIES IN THE CONSERVATION OF HISTORIC BUILDINGS
6 C O N T E X T 1 3 9 : M A Y 2 0 1 5 college quadrangle. The introduction of a stepped section influenced other significant post-war listed buildings such as the Alexandra Road housing estate in Camden and student housing schemes by Denys Lasdun. Moving from 20th-century conservation issues to those related to the early 16th-century, Andrew Harris describes in summary the continuing works at Hampton Court Palace to the Great Hall, the Buttery Roofs, Anne Boleyn Gatehouse, Base Court and Clock Court. Harris describes the repair work needed, some of which challenged the archaeological understanding and the uncovering of previously unknown repair issues and worrying structural problems. He explains how difficult aesthetic issues prior to and during the works were considered. The author’s overriding lesson on sensitive work of such complexity is to take nothing for granted. The IHBC member and former conservation officer for South Shropshire District Council, Colin Richards, promotes the revival of traditional building crafts in Shropshire and Transylvania. Members with quite long memories may recall Richards’ demonstration beehive brick kiln project at Acton Scott in use during a hands-on craft day during the Shrewsbury Annual School in 1998. In the article Richards describes his personal experience of conserving buildings and landscapes in the Welsh Marches as a platform for economic regeneration. He discusses the support of craft skills of contemporary relevance not only in the UK, but also revitalising heritage building crafts and craft training in Eastern Europe, and Romania in particular, through the work of the Transylvania Trust. Another international perspective is given by Andrew Smith’s account of the current social and economic context for conservation of the built heritage of Jamaica. The island is characterised by net emigration, a balance of trade deficit, and great disparities of wealth and influence. One-fifth of the nation’s income derives from ex-patriots. Problems of heritage management include opacity about the ownership of heritage assets; wanton and accidental destruction (for example of the island’s architecturally important historic courthouses); the perils of restoration in the primary interests of external tourism; and a lack of indigenous skills and understanding in the execution of repairs. Smith notes the good work being done by the Jamaica National Heritage Trust. He gives an example of a successful conservation project: the Iron Bridge, Spanish Town. But he concludes that ‘If conservation of the built heritage of Jamaica is to gather momentum, that will, as everywhere, only come from some force of intelligent belief in the mind of the people that it is needed: topdown can not work on its own, for small projects bottom-up probably can, but working together they could tackle the wonderful range of Jamaica’s built heritage.’ Conservation in the extreme cold of northern Canada was noted above, and the fourth paper in Transactions addresses equally inhospitable territory. Michael Morrison describes the physical legacy of the largely forgotten, abandoned and derelict whaling stations on the Antarctic Island of South Georgia (see Context 129, May 2013). It is argued that they may be suitable for world heritage site status. While they are considered a liability for the government of the island, interest in the heritage legacy is international, ranging from the South Georgia Heritage Trust, based in Dundee, to the Friends of South Georgia in the USA, and particular interest and support in Norway. The island is a British Overseas Territory but much of the heritage is Norwegian. Encouragingly their government is funding (along with British Foreign Office and South Georgia government contributions) a detailed survey of the current state of what remains. The prevailing official view is that what survives should remain in situ, that nothing should be removed, and that the sites should be allowed to decay naturally in this unforgiving climate. Finally, Katherine Watts explains the complexity and extraordinary collaborative effort in melding three different approaches to architecture, conservation and reuse for the Grade I listed Kings Cross Station to create an outstanding example of place making. The aim of conserving as much historic fabric as possible was constrained by the destruction of most of the station archives by bombing in 1941. The building history had to be pieced together using a few surviving original railway documents and on-site assessment. Completion of the operational work for the railway was required prior to the Olympics while still maintaining a full schedule of train services. The Main Train Shed, for example, was reglazed by removing previously installed seriously discoloured polycarbonate sheeting, greatly enhancing the experience of the main internal spaces, while still in use by travellers below. This work was complemented by the spectacular addition of the semi-circular new Western Concourse roof, which adds so much to the architectural expression of the station and to the anticipation of arrival and departure. The January/February 2015 issue of Natural Stone Specialist deals with stone for hard landscaping. Flametextured Blue Pennant stone features prominently (the Apple stores use it for flooring). It originates from the Bixhead Quarry in the Forest of Dean. But a considerable amount of the stone used in paving schemes is imported. Natural Stone Specialist reports that most of the stone used in hard landscaping projects in the UK last year came from China, which has overtaken India as the main supplier in the sector. Chinese granite seems now to be more popular than Indian sandstone for paving, influenced by price and currency fluctuations. Other imported stones being used include Belgian limestone paving from the Les Carriés de la Pierre Bleue Belge quarry. This is used extensively at Historic Chatham Dockyard, Kent, where the Command of the Oceans project, supported by the Heritage Lottery Fund, is regenerating the most complete example of a Georgian dockyard in the world. The series examining great British stones continues in the March issue
C O N T E X T 1 3 9 : M A Y 2 0 1 5 7 with the geological and quarrying history, properties, testing methods and uses of Ffestiniog slate. This article usefully isolates the characteristics of this slate, particularly for those who have a tendency to lump together all Welsh slate as a single product. Barry Hunt ably explains the reasons that this particular slate is considered one of the world’s best for roofing. C20 continues to provide an excellent mix of features, casework, reviews and illuminating event reports. The main feature worth highlighting in Issue 1, 2015, is a remarkable set of interwar photographs of the Boots d10 Factory in Nottingham, taken from the company’s archive. The building, by Sir William Owen in Beeston, completed in 1932–3, is widely seen as one of the most important industrial estates of the 20th-century. It was listed (now Grade I) as early as 1971. The photographs had a clear social purpose in promoting the company’s inter-war publicity message that machinery could be used to create a better society. The Boots archive is not currently open to the public, but a five-year programme to make the collection more accessible has begun. The issue features the life and work of pioneering designer and champion of design, Misha Black. His work will be familiar, even if unconsciously, to all Londoners. Black was responsible for all the Westminster street signs with their distinctive black-and-red Univers Bold Condensed lettering. The article illustrates and explains much more of the work completed up to his death in 1977. This included, for example, the once derided and ubiquitous house style of pub lettering for Watneys Brewery. These two examples perhaps do Black an injustice: in a career spanning more than 50 years, he did more than anyone else to shape the British design profession. As the director of Britain’s first major design consultancy, a leader of professional organisations, and as a prolific writer, teacher and lecturer, Black opened up the possibilities of 20th-century design. But in many ways he remains a mysterious figure. This article by Harriet Atkinson may help to dispel that. The most recent edition of The Victorian (No 48, March 2015) provides appreciations by former chairman Peter Howell and Louise Nicholson of the former Victorian Society secretary, distinguished architectural historian and general editor of the Survey of London, Hermione Hobhouse, who died in October last year. Hobhouse ran the society during a period of great change, and as the attitudes to Victorian architecture were changing from abhorrence and widespread dismissal to proper appreciation. These tributes provide an affecting picture of her impact on conservation. The cover features Tower Bridge. This iconic building (not an overused epithet in this instance) has been the subject of a major art exhibition (now closed) at the Guildhall Art Gallery, depicting the bridge over 120 years. For those who missed it, some the striking images from the exhibition are reproduced in the article. On the technical side, Moses Jenkins of Historic Scotland answers some of the questions that recur regarding the maintenance and restoration of fireplaces, chimneys and flues. Bob Kindred MBE From the manifesto of the Society for the Protection of Ancient Buildings, written by William Morris and others and issued in 1877 For Architecture, long decaying, died out, as a popular art at least, just as the knowledge of mediaeval art was born. So that the civilised world of the nineteenth century has no style of its own amidst its wide knowledge of the styles of other centuries. From this lack and this gain arose in men’s minds the strange idea of the Restoration of ancient buildings; and a strange and most fatal idea, which by its very name implies that it is possible to strip from a building this, that, and the other part of its history – of its life that is – and then to stay the hand at some arbitrary point, and leave it still historical, living, and even as it once was. In early times this kind of forgery was impossible, because knowledge failed the builders, or perhaps because instinct held them back. If repairs were needed, if ambition or piety pricked on to change, that change was of necessity wrought in the unmistakable fashion of the time; a church of the eleventh century might be added to or altered in the twelfth, thirteenth, fourteenth, fifteenth, sixteenth, or even the seventeenth or eighteenth centuries; but every change, whatever history it destroyed, left history in the gap, and was alive with the spirit of the deeds done midst its fashioning. The result of all this was often a building in which the many changes, though harsh and visible enough, were, by their very contrast, interesting and instructive and could by no possibility mislead. But those who make the changes wrought in our day under the name of Restoration, while professing to bring back a building to the best time of its history, have no guide but each his own individual whim to point out to them what is admirable and what contemptible; while the very nature of their task compels them to destroy something and to supply the gap by imagining what the earlier builders should or might have done. Moreover, in the course of this double process of destruction and addition, the whole surface of the building is necessarily tampered with; so that the appearance of antiquity is taken away from such old parts of the fabric as are left, and there is no laying to rest in the spectator the suspicion of what may have been lost; and in short, a feeble and lifeless forgery is the final result of all the wasted labour. Themagazineof the TwentiethCenturySociety Issue12015/£4.50 Amodernwonder: the1930sBootsfactory MishaBlack: pioneeringdesigner Seasidepleasures: C20Bournemouth 9772055503003 15 ISSN 2055-5032
8 C O N T E X T 1 3 9 : M A Y 2 0 1 5 Puddled Wrought Iron Puddled Wrought Iron Facts: • Corrosion resistant - Withstands atmospheric pollutants and even continuous immersion in salt water far longer than mild steel due to its fibrous nature. • Easy to form- High ductility makes it soft under the hammer, so it forges quickly. Traditional smithing techniques were developed specifically for wrought iron. • Easy to fire-weld-Withstands higher welding heats than mild steel and has its own built-in flux (iron silicate). • Matches closely the materials used in historic ironwork - If authenticity in restoration concerns you, there is no better choice. • Available in both standard and bespoke sections - Available in square, flat and round sections plus special sections such as handrails and glazing bar. We operate our own rolling mill. • Best quality - The puddled wrought iron we supply is of high quality and checked rigorously for anything that makes it not fit for purpose. • Authentic - Wrought iron has been recycled for many centuries by the same process we use. • Seems expensive? - No – steel is very cheap! Your work is worth the best, especially considering the ratio of labour to material costs! The finest material for traditional work, restoration work or conservation repairs enquiry@toppandco.com • +44 (0)1347 833173 • www.toppandco.com Architectural & Engineering Metalwork Conservation • CONSULTANCY • PROJECT MANAGEMENT • CAST & WROUGHT IRON • BLACKSMITHING • IRONWORKING • BRONZEWORKING • BRONZE, COPPER, ZINC • NEW WORK UNDERTAKEN • MILLWORK – INDUSTRIAL MACHINERY FOR FURTHER INFORMATION VISIT www.dorothearestorations.com OR EMAIL john@dorothearestorations.com Telephone: 0845 478 0773 Unit 4, William Street, St Philips, Bristol BS2 0RG 209102-11-14RBCON Dorothea.indd 1 24/10/2014 09:00 Tel: 07883 205704 • email: peter.meehan@hm-cc.co.uk www.hm-cc.co.uk Historic Metalwork Conservation Company Ltd “HMCC Limited provides conservation advice on everything from air frames to iron gates.” Direct your enquiries to Peter Meehan ACR
C O N T E X T 1 3 9 : M A Y 2 0 1 5 9 Material world WORKING WITH METAL Crystalline and coarsely granular Doulting Stone; honeycoloured Bath stone, turning golden at sunset; pink Weatherbed Ancaster stone; pale brownish-cream Stemford stone; lumpy Coral Rag; tawny-yellow, deep brown, greenish and greyish blue Hornton stone; fine-grained Barrington Clunch; greyishgreen Upper Greensand; shelly Portland Roach; brown-flecked, creamy white Hardwhite Ancaster; blue-grey, pale cream, light brown or buff-coloured Clipsham stone; cinnamon- and crimson-hued sandstone; whitish-grey Blue lias... The cussems, muffities, tants, wivetts and longbecks of Cotswold roofs; pink Suffolk limewash; sandcast lead; bright green copper; iron-hard ancient oak; Kent cottage weatherboarding; fish-scale oak shingles; delicate Regency ironwork; Georgian spun crown glass; orange-pink bricks; red, brown, biscuit or creamy-white terracotta; reed thatch with sedge ridge; Cumberland clay daubins... No apologies for the list. Building materials are wonderfully evocative. Much of building conservation depends on understanding how materials were used, whether it was in a long tradition or at the cutting edge of technology, and on how they can be repaired or renewed today, either with traditional methods or with the latest technology. In Context 134 (May 2014) we focused on timber conservation and repair. In this issue we look at metals: wrought iron, two iron bridges, cathodic protection, iron-frame mills and copper roofs. Read on if you are interested in sweetness of line, 500-year-old cramps, forged billets, green-stick fractures, makers’ marks, friction-grip bolting, hot-set riveting, depassivation, hydroxyl ions, impressed current, magnesium anodes, slow-burning floors, parabolic hog-backs, fish-bellies, Polonceau trusses and kaleidoscopic patina. If none of those grab you, what about the Swiss long-strip method, wood-core rolls and dummy welts? Now read on.
10 C O N T E X T 1 3 9 : M A Y 2 0 1 5 CHRIS TOPP Wrought iron, yesterday and today Wrought iron has not been made since 1974, but some is available and in recent years the blacksmiths of Britain have slowly taken up the ancient ironworking skills again. Wrought means ‘worked’, which refers to the method of manufacturing the metal by working repeatedly under a hammer. In the past the work of the blacksmith became known as ‘wrought ironwork’, a name that has persisted for the art form even though the metal in use may not be wrought iron. Today the common material of the blacksmith is mild steel, a cheap industrial product lacking many of the virtues of its ancestor. Wrought iron is a two-component metal consisting of iron and a glass-like slag. The slags are in effect an impurity, the iron and the slag being in physical association, as contrasted to the chemical alloy relationship that generally exists between the constituents of other metals. Wrought iron is the only ferrous metal that contains siliceous slag. It is to this slag that wrought iron owes the properties, which are of interest to the conservator and the blacksmith. There are essentially two types of wrought iron: ‘charcoal iron’, made in a charcoal fire and used from the iron age to the end of the 18th century, and ‘puddled iron’, made from cast iron in an indirect coal-fired furnace, and used since the dawn of the modern industrial era. Historically wrought iron has been worked by blacksmiths, using traditional techniques in both forging and construction, to make high-end decorative wrought ironwork. Today the term wrought iron is becoming debased and misinterpreted, to cover all ornamental ironwork, including cast iron and mild steel, as well as incorporating modern construction techniques. The difference in quality and value is enormous. Whereas it would be unthinkable to repair historic stonework with concrete or cast stone and Portland cement, it is common for historic wrought iron to be repaired using mild steel and electric welding. Wrought iron has been used in building from the earliest days of civilisation, wrought-iron door furniture being common in Roman times. The structural use of iron dates from the middle ages, when bars of wrought iron would be used occasionally to tie masonry arches and domes.This use of wrought iron in tension guaranteed its use throughout the ascendancy of cast iron in the canal and railway ages, as cast iron is strong only in compression.The ill-fated first Tay Bridge was of cast iron beams tied with wrought iron. The demand for higher dynamic loads in bridges and warehouse buildings, and the ever-greater spans of train sheds towards the end of the 19th century, led the designers of buildings to acquire the technology developed to build ships of iron, and create beams of riveted wrought-iron rolled sections. By the turn of the century this had led to buildings completely framed in wrought iron, and later steel girder sections, and cast iron was once again relegated to an ornamental role. Our main concern with wrought iron, however, will be in its application to gates and railings, frequently given an ornamental treatment by the blacksmith. There are wrought-iron railings inWestminster Abbey from the 13th century which, in essence, display all the characteristics, which we have come to know as ‘wrought Australian blacksmith Dave Fleming forging at Chris Topp’s
C O N T E X T 1 3 9 : M A Y 2 0 1 5 11 ironwork’. Although often lacking modern refinements such as symmetry and sweetness of line, the great age of British ironwork, known as the English style, began at the end of the 17th century. A French fashion for the baroque style in gates and railings swept the country houses of Britain following the import of craftsman byWilliam and Mary, and the greater part of our national stock of good ironwork dates from the early years of the 18th century. After the rise of cast iron as an ornamental medium, wrought iron tended often to take a secondary role, owing to its comparative expense, each piece being made by hand, while castings could be repeated infinitely once the patterns had been made.Technically, however, the craftsmen of the age of machines technically bettered their forebears, as indeed they must while making mechanical components. The ornamental blacksmith work of the 19th century displays a perfection of manufacture not seen before or since. After the introduction of mild steel, cheap because of its ability to be mass produced, wrought iron, and the craft skills associated with it, gradually disappeared in accordance with the general decline of craft standards in the 20th century.The last ironworks ceased production in 1974. From 1982 Chris Topp & Company and the Real Wrought Iron Company have made available a limited supply of puddled wrought iron.The subsequent years have brought a steadily increasing demand, as the blacksmiths of Britain have slowly taken up the ancient skills again. To the naked eye there is no visible difference between forged bars of wrought iron and mild steel (its modern day equivalent). However, wrought iron is not distinguished by its looks but by its working properties and its resistance to corrosion. Wrought iron is softer to forge, as it is workable at a higher heat than mild steel, making it more malleable under the hammer. It is wrought iron’s superior weathering properties that are most notable. Like all ferrous metals, wrought iron does corrode in certain circumstances, but evidence of its durability and long life expectancy is common in our towns and countryside.Victorian town house railings have wrought iron 200 years old. Vast ornamental gateways to 18th century great houses have wrought iron 300 years old. Stone cramps on Tudor bridges have wrought iron 500 years old.The simple fact that so much ornamental wrought ironwork survives, often with little or no maintenance, speaks volumes for the material. Problems with the rapid corrosion of mild steel in comparison with wrought iron were well known by the beginning of the 20th century.This prompted Matthew Verity to investigate in the USA. He concluded that the carbon in steel is responsible for its corrodibility, leading to the theory that removing the carbon removes the problem of corrosion. His efforts to produce pure iron resulted, not in a metal that was proven to have any resistance to corrosion, but which was very tough and malleable, and found favour in the emerging markets for mass-produced cold pressings: ARMCO iron. No convincing evidence was ever produced to back up claims of the non-corrodibility of pure iron, and pure-iron manufacturers themselves make no claims to its corrosion resistance.These same manufacturers offer other materials known as ‘weathering steel’ in Britain, or Far left: 19th century work restored using wrought iron New gates in wrought iron for Royal Chelsea Hospital
12 C O N T E X T 1 3 9 : M A Y 2 0 1 5 ‘Corten steel’ in the USA, for which they do make such claims. One of the chief uses for pure iron in today’s industry is as sacrificial anodes to protect steelwork tanks and ships, as it has been found to corrode preferentially to mild steel. Verity’s examination of puddled wrought iron and mild steel was a chemical analysis, which appears to have overlooked the presence of the slags. During the manufacturing process, wrought iron does not become molten, as do more highly refined metals, so impurities are included in the matrix of the iron rather than being separated and disposed of. At these high temperatures the impurities are turned to glass, and are commonly known as ‘slag’, consisting of carbides and silicates which give wrought iron its fibrous structure. Approximately 250,000 siliceous fibres appear in each cross-sectional square inch of high-quality wrought iron. The slag present in the structure of wrought iron inhibits corrosion in a number of ways: 1. Slags themselves are non-corrodible and serve as an effective mechanical barrier against the progress of corrosion. 2.The structure of the iron gives rise to a very rough (microscopically speaking) surface texture, which interlocks with the oxide layer, be it rust or mill scale, preventing it from flaking off the surface.The oxides act as a protective coating, preventing further corrosion. 3. Electrically speaking, where the slag appears on the surface it acts an insulator between the areas of reactive iron, retarding electrolytic action. When wrought iron is heated in the fire to a high temperature, the slag melts and covers the surface of the iron in a rather similar manner to flux. This glassy layer retards oxidation to the extent that the iron can be Polish blacksmith Arek Kropidlowski forging at Chris Topp’s Setting the shape of a hot scroll
C O N T E X T 1 3 9 : M A Y 2 0 1 5 13 heated rather more than purer metal without burning. For this reason wrought iron is more malleable to forge than any other metal. More important, this is why it is so beautiful to fire weld, the slag acting as a flux. Smiths often comment on a property of wrought iron, which renders it softer to forge than even pure iron. This is brought about by the slags, which melt within the iron at forging temperatures and act as an internal lubricant, reducing internal friction and hence resistance to distortion under the hammer. Given its limited availability and high price compared to mild steel, wrought iron is not always the first or right choice for all metalwork projects.Wrought iron is ideally suited for external and traditionally forged work. Although a number of blacksmiths and commissioners utilise these properties in newwork, its prime use today is in the restoration and conservation of historic ironwork. Modern conservation practice insists on the replacement of materials with like materials. As wrought iron is available for the repair and replication of wrought ironwork, it is not appropriate to use mild steel or pure iron. It would, for example, be considered wrong to repair historic stonework with concrete or cast stone and a similar principle applies to wrought iron. It is generally accepted that mild steel used on external work should be zinc coated by galvanising or hot spraying.The intricate forms and water traps of traditional decorative ‘wrought ironwork’ are notorious hotspots for corrosion.As neither of these zinc treatments is permissible nor effective with ancient work, the use of mild steel is effectively ruled out. Wrought iron is unlike cast, in that it is not brittle, and will bend rather than break. For this reason, wrought ironwork is frequently far more delicate, although years of paint can obscure this. Cast iron is most frequently identified by its repetitive nature and forms, which could be carved into a wooden pattern, but not made by hammer and anvil. Telling wrought iron from mild steel is often more difficult for the layman, as both will bend, and not break. Work in mild steel is often readily identified by the lower standards of workmanship often used. Look for evidence of electric welding. Mild steel is often given away by more active corrosion, which tends to run out of the joints and stain paintwork and stonework.This is seldom the case with wrought iron. Wrought iron may also be dated approximately by its texture. Until the very end of the 18th century, sections of wrought iron were derived by forging billets by hand or waterpower. This resulted in a more-or-less uneven surface texture, and very sharp corners.A foreshortened view of a bar displays well the irregularities of the surface. Rolled bars, on the other hand, produced from the beginning of the 19th century, are perfectly smooth, and the corners can display a small radius. Nineteenth-century wrought iron is known as ‘puddled iron’. Here are two tests for wrought iron: Nick bend testThe sample is nicked by a cold chisel or sawing to approximately half depth and doubled back cold to show the fracture.Wrought iron will exhibit a ‘green stick’ fracture, showing the grain,whereas steel will exhibit a smooth fracture plane. Polish and examine for grain. The sample is polished in a plane parallel to the length of the bar, and the exposed bright surface examined for signs of a grain caused by linear slag inclusions. Spark test The sample is brought to an engineer’s grindstone and the resulting sparks examined for colour and nature.Typically a puddled wrought iron will exhibit a more-or-less dead reddish spark, whereas steel will have more-or-less bursting white sparks caused by the inclusion of carbon alloyed with the constituent iron. Charcoal irons, however, may be confused with steel in this test as they frequently contain large amounts of carbon. Pure iron, while containing no carbon, can be identified by the absence of grain in the nick bend test. Chris Topp is a director of Topp & Co. Far left: A nick bend test for wrought iron The grain etched in wrought iron Far left: A magnified image of a cross-section of wrought iron A nick bend on mild steel showing the absence of grain
14 C O N T E X T 1 3 9 : M A Y 2 0 1 5 RICHARD BAISTER Dredge’s Victoria Bridge The 1836 Victoria Bridge in Bath has been dismantled, refurbished and uprated to meet current design codes, with its original elements being retained wherever possible. Victoria Bridge in Bath is a Grade II* listed structure which was originally designed and constructed in 1836 by a local entrepreneur James Dredge to link the lower and upper Bristol Roads over the River Avon.The bridge is thought to be the first of some 50 bridges of its type designed by Dredge and constructed in the UK, India and Jamaica. Only a small number of these bridges survive as many have collapsed and others have been demolished over the past 180 years. The bridge, originally constructed as a toll bridge for vehicular traffic, has a clear span of 42.5m and an overall width of 6m. Since a major refurbishment in 1946/47 it has only been used by pedestrian traffic. The bridge was closed to the public by Bath and North East Somerset Council in 2010 following one of its regular inspections where a number of cracked deck hangers were discovered. Subsequent inspections revealed that the bridge structure was further degrading, with new cracks and defects being noted on a regular basis. As a result of this and the risk of overall structural failure the towpath and river were also closed to the public in the autumn of 2011. Emergency temporary works were hastily installed to support the historic bridge structure, allowing the towpath and river to be re-opened to the public in January 2012. With the temporary support in place, the bridge structure was safeguarded. Proposals needed to be developed for the refurbishment or replacement of the bridge structure. Bath and North East Somerset Council appointed Temporary support provided by the internal Mabey bridge structure carried the weight of the original bridge. The completed, refurbished bridge (Photo: Jonathan Taylor) Capita Symonds tomanage theworks,withAECOM leading the engineering design for the project. Consultation began with the planning authority, English Heritage, the Canal and River Trust, the Environment Agency and the residents of Bath to determine appropriate repair proposals. Retention and refurbishment of the original bridge structure was seen by all stakeholders as the most Temporary support provided by the internal Mabey bridge structure carried the weight of the original bridge.
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