CONTEXT - The Association of Conservation Officers No 49 March 1996
ijiubor ~oof ijIHe Olo. 1fiimiteb Manufacturerosf HANDMADCEIAYROOFTILES StrengthandFrosttestedto BS402 OSI~ iJ:/mr'tlio1 OFCERTIFICATIDII BllliES Certificate No. FM 11616 BS EN ISO 9002 Registered Company (formerly known as BS 5750) Suppliedwithfullrangeof fittings,OrnamentalsO, astand KentPegs,Flat and CrossCambered.Availablien fivecolours,SussexRed,SussexBrown, Red,MediumAntiqueandDarkAntique. NOWAVAILABLE, TudoruniqueINVISIBLUENDERTILEVENTINGSYSTEM. Theessentiacl omplemento a HandMadeclaytileroof. GolfCourseClubhousefn TUDORtraditionalHANDMADECLAYROOFTILESin a mixtureof MediumAntique and Red colours. Acceptedin sensitiveareasand regardedbythe mostdiscerningspecifiersas the finest handmadetileon the market.Tudorgivethe highestgradeof serviceto our customerswho cantakepleasurein theirinvestmenkt nowingthattheyare addingto the qualityofthe environmenat nd our heritage. TUDORROOFTILECO. LIMITED DengeMarshRoad,Lydd,KentTN29 9JH 1991 Telephone01797 320202 HistoricHousesAssociation AwardWinner Fax01797 320700
CONTEXT Editor: Bob Kindred (Ipswich Borough Council, Tel: 01473 262934, Fax: 01473 262974) 4 Henley Road, Ipswich IPl 3FS, Tel: 01473 259441 Deputy Editor: Llz Marten (North Herts District Council, Tel: 01462 474411) 10 Kristiansand Way, Letchworth, Herts SG6 1UE Production Editor: Jonathan David, Tel: 01582 763415, Fax: 01582 467480 Context is published quarterly and is distributed to all members of the Association of Conservation Officers. © Association of Conservation Officers 1996 ISSN: 0958-2746 Published for the Association of Conservation Officers by Hall-McCartney Ltd, PO Box 21, Unit 7 Campus 5, The Business Park, Letchworth, Herts SG6 2JF, Tel: 01462 675848, Fax: 01462 679356 Nonmember subscriptions to Context Context is available to nonmembers of ACO at an annual subscription rate, including postage, of: United Kingdom Elsewhere £35.00 US$93.00 Subscription orders, together with remittances payable to HallMcCartney Ltd, should be sent to the address shown above. OFFICERS CONTENTS No49 News4 March 1996 NEW TECHNOLOGY FOR CONSERVATION Conservation goes underground. Aidan Duffy and David Wrightson 6 Infra-red thermography. Robert Demaus 8 "I have just one word to say to you ... Plastics". Anthony Walker 11 In search of concealed timber decay. Chris Cullen 13 Computer networks without cabling for listed buildings 16 Metal stitching at Doncaster's Com Exchange 17 I'm sure that crack is gwtting worse. Ian Hume 18 Cold comfort for lime in winter. Peter Hood 20 Looking after earth buildings. Bob Nother 22 A time to think and plan - about the conservation problems of rural non-domestic buildings. Carol Ryan 24 'Gazebo': Statutory protection, conservation & strategic planning -the Berlin experience.Judith Roberts Tyne oarsmen.John Pendlebury 25 28 SirTitus: other people's view of conservation. David Morton 30 'Supporting Columns': alternative ways of repairing old walls. Brian Morton 31 Conference report: 'Got a project?'; ACO East of England Conference. Francis Biard 34 ACOnews 35 Book reviews 3 7 THEASSOCIATIONOF CONSERVATIONOFFICERS PHOTOGRAPHS IN TIIISISSUE Front cover: photo: Bob Kindred p5: grille, photo: Ann Periton pp6-8: Gloucester Road station, photo, drawings: David Wrightson pp9 and 10: photos, thermographs: Robert Demaus pll: design for a Milk Bar, photo: the Sylvia Katz collection p12: Summerwood School, photo: courtesy of Bruce Martin pl3: plastics relay cabin, photo: courtesy of Percy Reboul pp15 and 16: timber decay, photos: Chris Cullen pl6: radio LAN, photo: Azlan Ltd p 17: metal stitching, photos: Casting Repairs Ltd pp18 and 19: structural monitoring, photo, drawings: Ian Hume p23: North Street, Bere Regis, photo: Bob Nother pp25-27: garden conservation in Berlin, photos: Judith Roberts pp28 and 29: oarsmen's monuments, photos: John Pendlebury pp31 and 32: drawings by Brian Morton The views expressed in Context are not necessarily those held by the ACO or the publishers. Neither the publishers nor the ACO shall be under any liability whatsoever in respect of contributed articles. The products and services advertised in this publication are not necessarily endorsed by the Association. Chairman: Mary King (Liverpool City Council, Tel: 0151-225 5678), 24 Beech Road, Holt Green, Ormskirk L39 6SJ Vice-Chairman: Alan Taylor (Staffordshire County Council, Tel: 01785 277282), 15 Village Gardens, Walton on the Hill, Stafford STl 7 0LL Consultations Co-ordinator: Sally Stradling (Cherwell District Council, Tel: 01295 252535, Fax: 01295 270028), Hickory House, 136 Main Road, Middleton Cheney, Banbury, Oxon OXl 7 2PW Secretary: Dr Richard Morrice (English Heritage, Tel: 0171-973 3132), PO Box 301, Brighton, E Sussex BN2 lBQ Treasurer: Robert Parkinson (West Oxfordshire District Council, Tel: 01993 770247), The Old Priory, Priory Lane, Bicester, Oxon OX6 7BG Membership Secretary: Gus Astley (Bath City Council,, Fax: 01225 477674), Manor House, Wells Road, Hallatrow, Bristol BS18 5EJ, Tel/ Answerphone: 01761 453047 BRANCH OFFICERS North: Keith Murray, Tel: 0191-383 3237 ext 2237 North West: Graham Arnold, Tel: 0151-934 3574, Fax: 0151-934 3587 Yorkshire: Bob Scriven, Tel: 0113-266 8782 CONTEXT49 West Midlands: Richard Cullimore, Tel: 01926 450000 ext 3107, or Peter Davies, Tel: 01782 742402 East Midlands: Graham Beaumont, Tel: 0115-982 3823 South West: Paul Dadson, Tel: 01823 255425 Education Co-ordinator: John Selby (South Cambridgeshire District Council, Tel: 01223 351795), 77 Deacons Lane, Ely, Cambs CB7 4PS Technical Panel Co-ordinator: Marion Brinton (Basingstoke & Deane Borough Council, Tel: 01256 844844), Development Department, Civic Offices, London Road, Basingstoke, Hants RG21 4AH. Publicity Officer: Kathy Baird (North Staffordshire DC, Tel: Business: 01939 232771; Other times Answerphone/Fax: 01691 636516), Edinburgh House, New Street, Wern, Salop SY4 4DB South: Julia Smith, Tel: 01296 382823 East Anglia: John Preston, Tel: 01223 463341 ext 2630 South East: Rob Fraser, Tel: 01273 712619 London: Rosemarie McQueen, Tel: 0171-798 2519 Scotland: Bernard Dee, Tel: 01334 653722 Wales: Neil Sumner, Tel: 01222 820028; Claire Deacon, Tel: 01437 764591 ext 5195 Northern Ireland: Laurence Manogue, Tel: 01232 23500 ext 279 3
NEWS COMMENT site open, so that other bodies can use it as a communication tool. Since 1 February a new secPROPERTYORARCHITECTURALHERITAGE? tionofthe RCHME'ssite has been operating, entitled Heritage News and carrying all kinds of informaRonald Reagan's "We start bombing the Soviet funding ofEnglish Heritage (and at one remove tion from other heritage bodies Union in five minutes" was a defining moment local authorities). Having pressed the Councils such as press releases, job adverin his Presidency. Did it show what was really ceaselessly for a decade to address the buildtisements, news of conferences on his mind? Will the "sale" of Admiralty Arch be ings-at-risk problem, English Heritage will make and publications. It is hoped that a defining moment for the heritage in the no money available for this in the coming year this service will expand to become a forum for news and infor1990s? Mr Portillo seems unable to distinguish for environmental works outside CAPS. mation on heritage matters in between property and architecture; between Abandonment of buildings-at-risk as it is England; one that is consulted second-rate 1960s office blocks and the Royal gaining real momentum is a particular kick in regularly by Conservation OfficNaval College, Greenwich. This may signal the teeth for Conservation Officers after so ers with the necessary equipment. what is on his mind - a depressing disdain in much effort has been expended on the surveys, our finest public historic buildings. If the the Risk Registers, negotiations with difficult WHAT IS THE INTERNET? College can be sold but the Arch cannot, owners and, for some, the first tentative and The Internet is a global network where will the line be drawn and what im- time-consuming steps towards an Urgent Works of computers linked by telephone pression does it give to owners of more or a Repairs Notice. lines. Only a minimum of equipmodest listed buildings of the Government's They are urged instead to apply for Lottery ment is needed to get connected. concern for our heritage? Next month, Gov- money - exploding the myth that this is addiAlthough any computer can be ernment departments become responsible tional to Government expenditure. Clearly it is used to connect to the Net, the ideal minimum is a 486 processor for their own property rather than the little becoming a substitute for it. How many build- with at least 4Mb of RAM(worklamented former Property Services Agency. ings-at-risk and how many environmental ing memory) and a 256-colour When Departments of State have to pay the schemes do they estimate will benefit under display,with sound facilities.Most full cost of maintaining their premises, how the Lottery? Individual owners don't qualify. It desk-top computers on the marmany more important historic buildings will should also be remembered that the only agency ket conform to this minimum be sold off? advising the Heritage Lottery Fund on such specification. A modem is also applications is ... English Heritage! needed (14,400 bps is the miniIS THE TREATMENT OF OUR HERITAGE If this is how it is to be in future - making the mum, 28,800 bps is twice as fast NOW JUST A LOTTERY? care of our heritage just a lottery, then the and means less time is spent waitHow much the Government really cares also Government and English Heritage should come ing for information to download to the computer) and a sound seems to be reflected in its attitude toward the clean. card with speakers. It is simple and inexpensive to add these FORTHCOMING a PC floppy disks written in Ap- and a summary of its research optional facilities to a desk-top ISSUES:DEADUNES pie Mackintosh format. OnlyWin- projects, ranging from the loca- computer. dows (or well known DOS for- tion and study ofmaritime wrecks, It is also necessary to subscribe ANDTHEMES mat) disks can be read. neolithic enclosures and redun- to the services of an Internet acFurthermore, the Editor can- dant military establishments, to cess provider. There are scores of Copy deadline for the Summer not compensate for other peo- air-photographic surveys cover- such organisations, and listings 1996 issue will be MONDAY 15 ple's fax machines which blur ing England's ancient monu- can be found in any commercial APRIL. Please adhere to this dead- the text to a point where it can- ments. The service can be used to magazine covering the Internet. line. not be scanned in to Context or order photographs, printouts and In return for a small monthly We will be looking next at the Newsletter. PLEASEDON'T Commission books. The message charge, the access provider 'Fostering Craft Skills' including JUST FAX ME. Any faxed copy page allows users to address e- should supply: how to encourage good crafts- not immediately followed up in mail to Commission staff or re- ■ use of the Internet for the price manship and how to ensure sur- the post with a clear hard copy quest further information to do of local telephone calls (some viva! and revival of skills for the will be rejected for publication. with their own research, making access providers give a certain proper conservation of historic use of the NMRCustomer Service number of hours free usage a buildings. Other contributions, CONSERVATIONON enquiry facility. month in return for the monthly experiences, technical notes and THE INTERNET As well as carrying regularly fee); case studies are welcome at any updated news about its own ac- ■ an e-mail facility, enabling an time (space permitting). Articles The Royal Commission on the tivities, the Commission is happy exchange of messages with other under 2,000 words are much pre- Historic;uMonuments ofEngland to carry information, press re- Internet users ferred. (RCHME) has launched a news leases, news items and reports ■ 24-hour technical support. If possible supply your copy and information service on the for other heritage organisations, They will also provide the softin word processed form on 3.5" Internet. Its World Wide Web offering a service to those which ware required to dial into the floppy disk. If you do so please pages can be accessed at: do not have their own Internet Internet, navigate from site to site make sure you indicate what http://www.rchme.gov. uk resources. It is also happy to set and download the material that is software it is written in on the The new service offers a wide up hotlinks from its site to other supplied by such information prolabel! If in doubt, the Editor or range of information about heritage-related services on the viders such as the RCHME,EngDeputy Editor will advise on what RCHME and its activities and is Internet. lish Heritage and the CBA. is desirable. illustrated with pictures from the Since its launch in late Octo- For further information on Despite the miracles of mod- NMR's extensive archives of ar- ber, over 45,000 separate 'visits' the RCHME Web site contact em computing, the Editor would chaeological and architectural have been made from around the Robin Taylor at RCHME Publiwish to remind potential contribu- material. The service also carries world to the RCHME's Internet cations. Tel: 01793 414619; etors that it is not possible to read details of all the its publications site. Now RCMEhas thrown the mail:pubs@@rchme.gov. uk 4 CONTEXT49
NEWS COUNIRYSIDESTEWARDSHIPSCHEME: REPAIRTSO1RADITIONALFARM BUILDINGS The Countryside Stewardship Scheme will be transferring from the Countryside Commission to the Ministry of Agriculture in April. MAFFintends to introduce a number of new elements to the scheme including grants for repair of traditional rural buildings. Rather than Countryside Stewardship's usual system of standard payment rates for specified work, building restorations will be treated as one-off special projects because they are likely to be highly variable. Grant payments will be based on a percentage of actual costs against an agreed restoration plan. MAFF is currently considering criteria for assessing acceptability and local priorities for grant: ACO will be involved in this process along with ACAO and English Heritage. MAFFwill be introducing new consultation arrangements to seek CORRECTION Myapologies for incorrectly naming the author of 'The Glazier's Role' ( Context 48) asAlbert Fisher views on applications involving traditional buildings. It will be writing shortly to all local authority Conservation Officers and archaeological officers to explain these in detail. It is intended that all such applications will be copied to the Conservation Officer and archaeologist for an initial rapid response as to whether the building is a suitable candidate for restoration and brief comments on proposals. Officers will also be given the opportunity at that stage to request further involvement in the case. If so, they will be consulted in detail on the restoration plan. listed buildings consent will still be required and the Conservation Officer will clearly play a role in such cases, but these additional arrangements give greater opportunity for local and specialist views to be considered in all cases. when it should have been Alfred Fisher. My apologies. Mr Fisher, who is the Conservation Advisor on stained and leaded glass to the National Trust and was co-founder TIIE CONSERVATION PORTFOIJO In the March 1996 edition of the Portfolio are: Clement Brothers - Steel Window Manufacturers and Glaziers Sibert TechnologyManufacturers and Suppliers of Decay Detection Equipment D. W. WindsorHeritage Style lighting and Street Furniture Peter Cox Scientific Services - A Division of Peter Cox Group Specialising in New Technologies using Non Destructive Techniques such as Thermographic Surveys and Dry Rot Management Cranleigh Brick & Tile Company LtdRestoration products CONTEXT49 and Partner of Chapel Studio, has recently changed address and is now in practice at 9 The Highlands, Rickmansworth, Herts WD3 3EW. Tel: 01923 770891. Unfortunately, the paired illustrations on page 9 of the article were printed on their sides, but Mr Fisher has also pointed out that he intended his caption for the top illustration to read: "The superb texture of 18th century Crown Glass mixed with earlier Broad Glass". Editor. RESURGAM Hutton &Rostron Environmental Investigations Ltd has recently formed a new division, Resurgam, to manage the Historic Building and Site Services of the Department of Conservation Sciences of Bournemouth University to provide a combination of diagnostic and advisory skills, laboratory facilities and information systems for the care of historic buildings. Resurgam will offer a comprehensive service in building performance investigations, especially in historic structures and their materials, conservation planning, maintenance management, archaeological site conservation and the conservation of decorative features and finishes. For example, currently, monitoring systems are in place to take regular telemetric readings of critical building performance characteristics at Windsor Castle. There is also a partnershipunder the European EUREKA project to develop environmental methods of controlling building decay and, with Bournemouth University, operate a DTI Teaching Company Scheme for the development of movement sensors and an on-line knowledge-based method for the diagnosis of masonry decay. A SHORTHOIIDAY FOR'M'LEARNED FRIEND' It would appear that at the risk of considerable disruption to the Government of the United Kingdom, the Courts of Justice decided not to sit, and the current Parliamentary session was suspended to permit 'M'Learned Friend' a short break. This enables Conservation Officers to sit down and read his excellent book knowing they will not have to worry about missing any significant legal developments in the last quarter! 'M'Learned Friend' will return refreshed in June. COVERSTORY Conservation Officer having just heard of English Heritage's expenditure plans for 1996-97! THINGS SEEN Spotted in Kreuzberg, Berlin, by Tim Penton, this security grille shows that it is still possible to make witty additions to old buildings. LE1TERS CHOICEWORDS Dear Editor Forgive this attempt to bring a little levity to the earnest pages of ourjournal. Throughourfrequent appraisals of the lists we come across some intriguing and obscure references to architectural details, one of which I include below. Do any other Association members have some similar examples to offer? Spencer Cottage, Coleford, Devon Grade II*- "Hall has late C 16-early C 17 fireplace built of stone rubble including many squared blocks of volcanic stone. It has a C20 replacement timber lintel, an CJB inserted cloam oven and a hearth of upended states" (sic). David Morgan, Exeter 5
6 ONSERVATIONGOES UNDERGROUND Aidan Duffy and David Wrightson describe terracottta and steel conservation at Gloucester Road Tube Station. London SW7 Gloucester Road Tube Station is situated in the heart of London and serves the District, Piccadilly and Circle lines of the city's underground system. The station comprises two separate buildings -one faced in buffbrick, the other in glazed red terracotta, and it is the latter building that is the subject of this article. The building is one of forty similar stations designed by Leslie Green and was built in 1906. It consists of two main elevations, one facing onto Courtfield Road, the other onto Gloucester Road itself. Both facades are similar in appearance with square pilasters surmounted byan abacus at ground floor, this supporting an entablature over which are bull's eye windows; at the top of the building is an architrave, frieze, cornice and parapet. The original condition of 1:re:··:11:1LS --:Of'1 ST1-\:-rl'CliEf)NS N'.' 14 15 .. It 1.6 SCJ\L[ • I INCH -·To-ONE FCJOT the building is illustrated in the photograph which was taken in 1928. The cladding now exhibits a number of problems, the most serious of which is Figure 1: Original drawing from the archive of London Underground Ltd The steel members are large enough to take the load from the (intended) building above. CONTEXT49
the cracking of many of the glazed terracotta units. lhis isparticularly severe on the pilasters which are located at ground floor level. In addition, and as a direct result of cracking and spalling of the terracotta in the past, there are large areas of plastic mortar repairs in different areas of the building. All of these repairs, together with some isolated areas of terracotta, have been painted with a red gloss paint with the intention of visually blending the repairs in with the red glazed terracotta. Other existing problems include the presence oflarge amounts of reprecipitated calcite under many projections (such as the cornice) and a surface coating (probably an organic water repellent) on the Courtfield Road facade. Previous engineering reports had concentrated on the problem of terracotta cracking and had attributed this to the corrosion, expansion and consequent movement of a steel frame inside the structure. The recommendation for dealing with this was to remove all terracotta and brick from around the steel frame, blast and protect the frame and replace the brick and terracotta. Due to an umber ofproblems with this strategy including its high cost and associated conservation philosophy difficulties (most terracotta would be irreparably damaged in the process), the client, London Underground Ltd (LUL),sought a second opinion. In July 1995 LULappointed a multidisciplinary team including architects, engineers, scientists, metallurgists and conservation specialists, in the form of Lawrence and Wrightson, Carrig, Mott McDonald and the LUL's own in-house staff, to investigate alternatives to the 'dismantle and rebuild' strategy. The approach adopted by the team was comprehensively to determine the causes of damage and to base all conservation strategies on eliminating these asfar as possible. The first, and most important, step involved determining the cause ofcracking of the terracotta through structural investigation. lhis task was facilitated by detailed original drawings of the steel frame (see Figure 2) which showed the precise location, dimensions and construction of each stanchion and beam in the station. The condition of these structural members was determined by opening up a number of areas where the terracotta was already badly damaged. The openings revealed that approximately 3 mm of rust had built up on the outside faces of the flanges and webs of the stanchions and beams. lhis rust build up had pushed against the tightly packed mortar and brick fill v v electrolyte(wetmortar); v v [7 v v ~ v fowof~ctrons v [7 [7~~ anode(+)' 'J ~ c l-7777777J'7T,,.. rust CONTEXT49 Figure 2: Typical constructional detail. around the steel (see Figure 3) and forced it apart, resulting in turn in cracking and fracturing of the glazed terracotta facing of the building. The cause of this is the ingress of moisture into the structure of the building, the wetting of the steel, the formation of corrosion cells and the ensuing deterioration of the steel by rusting. The primary locations of water ingress included the parapet and upper cornice. Significant amounts of reprecipitated calcite showed that water was entering the structure, dissolving the free lime and -calcite in the bedding mortar and terracotta void packing, and reprecipitating as hard white calcite where it exited the structure under the cornice. Another source of water ingress was damaged or blocked internal down pipes. The solution to arrest the ongoing corrosion and terracotta cracking totally is thus deemed to be the exclusion of water, as far as possible, from the structure. lhis is achieved by replacing all internal down pipes, lead flashing the Figure 3: Left: the constructiuon process Right: The cathodic protection of steel using a sacrifical anode. v v 7
8 top of the parapet wall and by applying mastic to the skyward joints of horizontal projections such as the cornice. Because it is impossible to eliminate moisture completely from the fabric of a building, it is not possible to arrest the process of steel corrosion totally without protecting it. For this reason itwas decided to stabilise the steelwork by means of cathodic protection. This involves the application of a small electric current to the steel to make the frame act as a noncorroding cathode. Although this technology dates from the middle of the last century, it has never been applied to a structure of this nature in the United Kingdom (a similar smaller structure has been cathodically protected in Dublin). Steel and iron corrosion is an electrochemical process where electrons move through an electrolyte (usually saltrich water) from an area called an 'anode' to one called a 'cathode' (see Figure 4). At the anode site the product of the reaction is commonly known as rust, and this grows and expands as the corrosion process proceeds - it is this characteristic ofrustwhichisofprimaryconcerntothe conservator as it generally results in the spalling of masonry in the vicinity of the corroded area. Other associated problems such as the loss of uncorroded crosssectional area, or a decrease in the structural integrity of the corroded element, are generally not an issue in load-bearing masonry structures, but may be a considerable problem in reinforced concrete structures. Steel which corrodes in this way can be cathodically protected by impressing a flow of electrons from an external 'sacrificial' anode towards the metal being conserved, which acts as the cathode (see Figure 4). This totally eliminates any possibility of corrosion of the conserved metal since the entire surface of the metal now acts as a cathode (hence the name 'cathodic protection') and there is no opportunity for the formation of anodes on it. In practice the cathodic protection system consists of long thin anode rods within the masonry fill and adjacent to the corroding steelwork. Each rod is connected into a circuit and direct current is impressed between these anodes and the steel frame itself. The frame thus acts as a large cathode and is therefore protected from further deterioration. Once the structure has been stabilised it isthen practical to carry out a restoration programme involving the replacement of cracked and repaired terracotta units with new blocks; these have already been manufactured by Shaws of Darwen. In addition to lead flashing the parapet and application of mastic to skyward joints, the paint and water repellent coating will be removed from the terracotta blocks, and the terracotta facade cleaned. It should be stressed that all of the cleaning and removal techniques have been assessed both in the laboratory and in situ to ensure that no damage is caused to the glaze or body of the terracotta units. For example, it was found that the terracotta had been treated at some time in the past with a protective coating. This had since failed, the once transparent application had become cloudy and cracked in appearance. It was decided to remove this coating for two main reasons; it was detracting visuallyfrom the integrity of the building and the coating did not serve, and could never have served, any useful purpose since the glazed tile is almost totally impervious to water penetration in the first place. Before effective removal could be carried out it was important to identify the chemical make up of the treatment so that the most suitable solvent could be chosen for its removal. From experience and by a process of elimination in the laboratory it was determined that the treatment was most probably a polyurethane-based water repellent. A product containing suitable organic solvents was chosen to remove the failed coating. The solvent was then successfully tested in situ on the building to ensure that its practical use did not lead to any nforeseen problems. It can be seen that the methodology adopted, a rigorous assessment of the causes of damage and the design of a strategy for their elimination; has resulted in a clear definition of the problems and their solutions. Recommendations have been chosen to minimise the extent of intervention -rather than 'dismantle and rebuild', the new strategy could be described as 'stabilise and restore'. This approach represents a less intrusive and more sympathetic approach to the conservation of early steel-framed buildings. Dr Aidan Duffy BA BAJ is an engineering graduate of Trinity College, Dublin, and is one of the principals of Carrig Conservation Engineering which is based in Dublin, but also has offices in Florence and Manchester (tel: 0161-928 8428); David Wrightson MCD BArch DipCons (loASS York) is a partner in Lawrence & Wrightson Architects and Landscape Architects, Voysry House, Barley Mow Passage, Chiswick, London W4 4PN. INFRA-REDTHEMOGRAPHY Robert Demaus discusses a technique with many uses for the Conservation officer. In previous articles ( Context 35, p28 and Context 39, p25), I discussed the applications of ultrasound and micro-drilling for the assessment of decay and structural weakness in timber. In this article, I will be looking at the use of infra-red thermography in a wide range of building diagnostic applications. Allbodies radiate energy continuously in the form of electromagnetic waves: the strength of this radiation in the infrared range is related to the thermal properties of the body, its surface temperature, and its emissivity. The components comprising that body absorb, transfer and reflect the energy in different ways depending on their composition. It is the thermographic camera's ability to identify these often minute differences that makes it such a powerful diagnostic and archaeological tool. The sensitivity of the latest equipment allows a huge amount of information to be collected about the original construction, historical changes to the structure, structural failures and decay and damp problems hidden behind the outer surface, as well as variations in that outer surface that are not visible to the naked eye. It can be seen therefore that the technique can be as valuable for its archaeological as for its structural information. Thermographic cameras are generally similar in concept and appearance to a large hand-held video camera. Wide angle, telephoto and macro lenses are available to suit different operating conditions and the colour images are stored on either video tape or discs for subsequent analysis and printing. The control unit has facilities to add spot and difference temperatures, isotherms, magnification and adjustments to image contrast. The essential and very expensive differences from a conventional video camera are that the camera contains a photo-voltaic temperature detector cooled to 80 K (approx.-193°C),andthelensesaremade of germanium dipped in gold. The very low temperature isneeded to achieve the sensitivity required (within 0·08°C at 30°C ambient temperature). Infra-red thermography has an CONTEXT49
established use in buildings as a quick and very cost-effective method of detecting excess heat loss, which can in itself be just as important in a historic building as any other. Recent and continuing research has demonstrated that it is also extremely useful in a wide range of other applications including the location and/or assessment of the following. CONCEALEDSTRUCTIJRALTIMBER FRAMES The building illustrated is typical of thousands in towns and villages throughout the country. It has been rendered externally and lined out internally, so there is no easy way of determining how it was built, orwhat alterations have taken place. The window positions in the gable elevation suggest it was originally timber framed, but not necessarily whether it is still framed or, if so, exactly where the structural members are. The thermographic image shows very clearly the structure behind the render. Various points that become immediately apparent are: ■ the gable elevation is timber-framed, ■ the windows do not relate to structural members, ■ the framing pattern changes halfway up the wall, ■ the frame is independent of the chimney in the comer, ■ the front elevation has been rebuilt in brick, ■ there do not appear to be any major structural defects such as cut or missing principal members. All this information can be obtained inI t I [ CONTEXT49 stantly from street level, allowing far more informed decisions to be made about any proposed changes or works to the building. Simply as an archaeological tool it is of enormous value, but once the structure has been so accurately defined, it is also possible to test the condition and integrity of every member of the frame using micro-drilling techniques (see Context 39, p25) through 2mm pilot holes drilled through the render. Any repairs found to be necessary can be carried out without removing any more render or internal finishes than absolutely necessary. To assess the structure and condition of this building in any otherwaywould involve stripping allthe render offthe outside, or removing much of the internal finishes and decorations, and then replacing them, with all the concomitant loss of original or historic fabric, disruption and expense. How many times have important, or at least perfectly satisfactory, external and internal finishes been destroyed unnecessarily? CONCEALEDSTRUCTURALJOINTS, OPENINGSETCIN MASONRYWALLS Thermographic imaging reveals the differing thermal properties of materials within a wall, thus identifying where there have been changes to the structure. This can be very valuable in an archaeological/historical survey of a building, but can also provide vital structural information. As an example, at a church in midWales which has suffered massive stability problems, and which it was intended to underpin, thermography revealed a straight joint with dressed quoins in the 23 22 21 20 19 18 17 16 15 14 13 12 11.3 NEWTECHNOLOGY FORCONSERVATION (8) (8) stonework of one side wall, for which there was no visible evidence. This has significant implications for the pattern of underpinning. Similarly,old window and door openings are clearly shown by thermographic imaging. These reveal a great deal of the history of a building, and have considerable structural implications if new openings are proposed. BOND FAILURESAND MOISTURE INGRESSIN PARGETTING,HARLING AND RENDERS If a render becomes partially detached from the mass of wall behind, it shows clearly on a thermographic image because it warms up and cools down more rapidly than the fully bonded areas of render. This allows a very quick assessment of the condition of renders without the expense of scaffolding or specialist access equipment. Very often, it can be demonstrated that only localised repairs are necessary, which can be particularly important in areas where decorative pargetting is prevalent. LOCATIONAND TRACKINGOF LEAKS,RISINGDAMPETC Damp, and its causes and effects, are frequently misdiagnosed in buildings. A leading independent expert in the field has stated that around 70% of remedial damp treatments are unnecessary and, of those that are, around half are unsuccessful. The effects of excess moisture can Photograph and thermograph of typical building (described in the text) 9
10 Photograph and thermograph of timber stud and render 'battlements' manifest themselves a great distance from their source, and it can be extremely difficult to locate the course of moisture movement through a building. Standard commercially available moisture meters are notoriously unreliable, and in any case usually cannot provide a sufficiently broad picture to establish large-scale patterns of such movement. Unless these sources are located and remedied, other problems that may exist within the building, such as timber decay, cannot be satisfactorily dealt with. Equally, changes to the internal environment of the building, such as the installation of underfloor heating, can have unpredictable effects on moisture patterns which thermal imaging can monitor. Where remedial treatments such as injected damp-proof courses have been used, faults and breaks in the barrier can be detected. CONDITION OF AND HISTORIC REPAIRSTO ORNATECEILINGS Very often it is not the plasterwork itself that is of concern, but the condition of the supporting structure that requires investigation. Ornate ceilings can be evaluated on the same basis as the assessment of frames behind render discussed above, again using a micro-drill to assess the condition of the supporting structure once located. Temporary heat sources are sometimes required to achieve the necessary temperature differences. There is some indication that thermal imaging may be able to differentiate between lime-and gypsum-based plasters, and identify previous repairs and alterations, perhaps due to differences in emissivity and density, but further research is required. STRUCTURALFAILURESIN BRICKWORK Loss of bond between facing and stock brick behind, which was never more than mildly affectionate in many a Georgian speculative development, can be identified by thermal imaging before failure becomes all too obvious. Other possible problem areas such as decayed bonding timbers can also be located. Not all bulges in walls are structurally serious, but how many buildings have been unnecessarily underpinned and/or rebuilt by over-cautious or under-informed (or both and worse) engineers and surveyors who have failed to identify the real problems? ARCHAEOLOGICALRECORDING FOR LISTING PURPOSES, CONSERVATION AREASETC The wealth of information provided by thermographic images, and the speed and ease with which that information can be obtained, makes this technique an invaluable tool for resurveys etc. A street elevation of thirty houses can be recorded in less than 30 minutes, simply by walking along the opposite side of the street, with no access equipment and no disturbance to occupiers or others. This provides a record of the original method of CDnStructionand any subsequent changes to the building. So many buildings have been updated and altered over the centuries that this kind of information allows a far greater understanding of the development of a street or village. MONITORING OF FRAGILEMURALS AND REMEDIALTREATMENTS Thermography has proved itself useful in preliminary diagnostic investigations for the conservation of murals. Very often the fragility of murals, particularly in • churches, is caused not so much by the materials of the mural itself, but by the prevailing environment and problems with the substrate. Many of these problems such as salt crystallisation and mould growth are caused by moisture and thermal variations through the fabric of the building. Thermography can identify and monitor these patterns enabling a far greater understanding to be obtained of the mechanisms creating the problems. The above gives a general view of some of the many applications in which infra-red thermography gives valuable information. The power of the technique lies in its speed and ease of use from ground level, and its ability to provide a broad picture of patterns of structure and CONTEXT49
failure, as well as more detailed close-up information. Further investigation by other nondestructive techniques may be required, but these can be restricted to where they are needed. There is inevitably a downside, which is the equipment's extreme sensitivity to environmental conditions. Rain,wind and sunlight can all affect the level and reliability of information obtained. Sunlight on the elevation under inspection results in excessive reflected heat from the surfaces, making external survey impossible, but on the other hand, often creates sufficient thermal gradient to allow the necessary information to be obtained by an internal survey of the wall. In unheated buildings such as churches, solar gain creates sufficient thermal gradient to reveal construction details buried within thick stone walls. In heated buildings, the greatest amount of information is obtained on cold nights when the temperature differences across a structure and between different materials are most marked. Rain cools the surface and reduces emissivity: wind also tends to reduce temperature differences. • This sensitivity may seem to render the technique somewhat useless for external assessment in this country, but in fact the problems can usually be overcome by careful planning. The full potential of infra-red thermography has yet to be determined, and research is continuing, but there are many other applications for the technique, such as the location of failures in stone cladding and curtain walling. It is quite clear that a huge amount of data can be obtained: the skill lies in turning raw data into valuable information. In many cases, the sheer volume of data obtained can actually obscure that which isrelevant to the particular information required. For example, thermography will pick out changes in the size of aggregate used inarenderbecauseofthedifferingthermal masses involved, and also differentiate between lime and cement renders by virtue of their different moisture contents. This may be of interest and value, but can obscure or confuse the assessment of bond failure for which the particular NEWTECHNOLOGY FORCONSERVATION @ @ survey was commissioned. Some applications, such asthe location oftimber framing, is fairly easy to interpret, others like the assessment of bond failure in brickwork, require a high level of experience to interpret reliably. Ifloss of historic fabric, disruption and costs are to be minimised, it is vitally important that as much information as practicable is available on the construction, historical development and condition of a building before repairs or alterations are carried out. Would you like to be operated upon by a surgeon who had but a vague knowledge of your physiology, medical history and current ailments? .. Robert Demaus is a partner in the Demaus Partnership and may be contacted on 01568 615662. "IHAVEJUSTONEWORDTO SAY TO YOU ... PIASTICS" Mr McQuire in The Graduate (1967) Anthony Walker discusses and area of modern construction where preservation may not always be possible A very simple word for an incredibly varied range of materials, loved by some and hated by others but attracting a rapidly growing interest from collectors and conservators. Until recently polymers have only been of interest to Conservation Officers and building conservationists to tl1e extent that as silanes, epoxies and other sinillar products they are used to stabilise or repair more traditional materials. That situation is now changing rapidly for not only is the importance of plastics artefacts now widely recognised but also post-war buildings now being consideredfor listing incorporate a substantial proportion of plastics from cladding to paints, decorative laminates to door furniture, dpcs to plumbing. Plastics have been used in buildings throughout the century and from the 1950s onwards have invaded every aspect of construction. Any approach to the conservation of buildings of the 20th century will require an understanding of the materials, their CONTEXT49 historic significance, their durability and the processes of degradation. This article provides an introduction and some sources of further information. During the 19th century natural polymers were used more widely in buildings than is generally recognised. Gutta Percha, shellac and Bois Durci provided speaking tubes, coatings and A design for a Milk Bar by Maxwell Fry from the 1938 Rexine catalogue. 'Jbe Sylvia Katz collection. mouldings and had many other uses beside. At tl1e beginning of the 20th century the first fully synthetic materials were produced with discoveries by Baekeland in America and Swinburne in England leading to phenol formaldehyde moulding powders and resins. They became known under various trade names: Bakelite, Formica, Wareite among others for lan1inate sheets and Damard from Swinburne's Damard Lacquer Company for coating brass and other materials. Cellulose nitrate, discovered by the middle of the 19th century and known as Parkensite, Xylonite and most commonly Celluloid, was also used as a coating and formed the base for many paints during the 1920s and 1930s. One particularly unusual use was to provide a light-sensitive wall coating onto which a photographic image could be projected and fixed which was promoted as a time saving means of achieving a decorative finish. There is at least one recorded use of this technique at Wells Coates' Embassy 11
12 Court in Brighton where a mural by McKnight Kauffer was projected on to the walls of the entrance hall. The end of the 1920s saw a break through in the understanding ofthe nature of polymers leading to the emergence of a series of tailor-made plastics. Vinyls, acrylics, Cellophane and Nylon were among the many materials which were promoted for the building market often using well known architects such as Maxwell Fry or F. R. S.Yorke to give their name to designs incorporating the new materials. Casein, a milk-based polymer, was used for a wide range of handles and bathroom fittings in mottled colours while the dark laminates based on phenolformaldehyde were supplanted by a brightly coloured range using urea or melamine-formaldehyde resins. Reputedly the first use of ureaformaldehyde sheets was for the wall linings to several studios in Broadcasting House where, because of an edict issued by the Controller banning the use of imported goods, Wells Coates, Raymond McGrath and Serge Chermayeff had to find a substitute for the German manufactured Trolit which led to their discovery of Bead produced by Beetle Products of Oldbury and believed to be so named because it "beat all". Many materials found new uses in the inter-war period and fine glass filaments were produced for the first time in a form suitable for reinforcing plastics. Early attempts to use these in laminates failed since the polymers were thermosetting exothermic materials which in curing precipitated water. In order to control the steam produced they were manufactured at high pressures which the delicate glass fibres could not withstand. By the end of the 1930s coldcuring polyesters had been discovered and were developed rapidly under wartime conditions to provide military necessities including radomes and boats. Manufacturers of many other polymers, such as polyvinylchloride for electrical cable insulation, also benefited and by the end of the war there was a plastics industry with enormous spare capacity. Like the aluminium producers, plastics manufacturers turned to the building industry as an outlet for their surplus goods and often materials such as GRP transparent sheeting, which when first produced had a life of only two or three years, were foisted on an unsuspecting industry and gave the materials an undeserved reputation as cheap and unreliable substitutes for more traditional materials. There were, however, those who were enthusiastic about plastics in their own right. The Hertfordshire schools programme concentrated on prefabricated systems using simple frameworks with infilling panels which could be interchanged and rearranged to give the full flexibility in initial layout and subsequent use. Bruce Martin, known for his work on modular co-ordination, was in the architects department and saw plastics panels as an ideal material. He worked on the development of Holoplast panel systems one inch thick which could be used for internal and external panels, filledwith sand to provide sound insulation and which, according to Singer, even had heating elements incorporated in them. Sadly Summerwood school, which Martin designed, burnt down but any other examples of the use of these panels would be of considerable significance even if only so that they can be recorded. The use of plastics for cladding came to be of major significance at least in the minds of designers. The benefits of lightweight self-supporting and ostensibly low maintenance walling were self evident but the practical problems of fire Summerwood School using Holoplast panels. By courtesy of Bruce Martin. resistance and large mouldings were more intractable than was realised at first. By the early 1960s there was considerable interest in the development of threedimensional forms often inspired by car and lorry bodies. Mickleover Transport produced a series of relay cabins for British Rail which was developed as a two storey version for a telephone exchange at Tyseley and for laboratories in the Arctic. At about the same time John Davidson in the GLC Architects Department was very keen to develop a fully industrialised housing system, partly because a shortage of professional staff was delaying the housing programme. A prefabricated steel frame with lightweight cladding was seen as the solution and, various options having been considered, the SFl system was selected. This used a GRP panel manufactured by Indulux and four buildings (all now demolished) were constructed. While not of major architectural value they were seen at the time as heralding a technical breakthrough and are thus of considerable interest to the industry as well as in the history oflocal authority housing and for that reason it has been possible to save some panels for the Science Museum collection. Possibly the most architecturally significant building to use GRP cladding is Sir James Stirling's extension to the Olivetti training college at Haslemere in Surrey. Here, again, other materials were first considered but the benefits of plastics shells outweighed other considerations and were used to provide an extruded image consistent with the brief which required flexibility to extend the two arms to an unlimited degree. The detailing to achieve this smooth image relied on a simple butt joint between the panels which was reported as a source of problems from the outset and alterations have been considered which would change the profile, thus detracting from the original concept. Decorative laminates boomed in popularity in the post-war period. Warerite's successful lamination of a Nicholas Bentley cartoon for the Coronation Scot in 1939 is believed to be the first of its kind and after the war a wider variety of panels was produced ranging from maps to murals. Repeat patterns used offset litho and silk-screen printing techniques but individual panels were actually hand crafted and despite their impersonal finish are indeed works of art worthy of preservation. Unfortunately, th<';Yare only too often CONfEXT49 t
discarded on the assumption that they are a mass-produced factory product. Apart from these dramatic examples plastics became widely used to replace more traditional materials, sometimes imitating their appearance but often establishing their own image. These are now to be found in virtually every aspect of the finished building and its construction. Many plastics degrade quite rapidly despite an image of indestructibility. Museum collections have already suffered major losses and polymers such as cellulose esters develop an acidic bloom which can affect other nearby materials. While most of those used in building are less aggressive, many plastics are difficult to repair or have been found to be hazardous materials which need to be replaced. The question of appropriate conservation raises philosophical issues: while the principle of the retention of original material may be very relevant to a material where each piece is unique, such as stone, is it still true where a manmade polymer can quite easily be replicated. Record rather than retain may be the most appropriate response in many cases. For the Conservation Officer it is a matter of knowing what may be of interest; early Bakelite door knobs will often have been replaced by more modem aluminium handles but they already have a collectors' value and before long an interior which still has plastics door Prefabricated Relay Cabin using GRPpanels by Mickelover Transport. By courtesy of Percy Rebottl. fumiture from the 1930s will probably be worth preserving. Decorative laminates with one-off designs are certainly worthy ofa second look and even plastics cladding systems can be of sufficient interest to specialist groups which would like to record their presence and in some cases arrange for sample panels to be kept in museum conditions. Some buildings, such as the rail relay cabins (the author would be very interested to learn ofany surviving examples), might well be appropriate for listing on account of both technical innovation and their interesting building form. SOURCESOF INFORMATION. Plastics Historical Society 11Hobart Place London SWl WOHL, tel: 0171 245 9555 Cook, Patrick, and Slessor, Catherine: Bakelite. Apple Press, 1992. NEWTECHNOLOGY FORCONSERVATION ® ® Katz, Sylvia: Plastics. Studio Vista, 1978. Katz, Sylvia: Classic plastics. Thames & Hudson, 1984. Kaufman, M: The first century of plastics. ThePlastics&Rubberinstitute 1963. Sparke, Penny (Ed.): The Plastics Age. Victoria and Albert Museum, 1990. Walker, A.: 'Fiber-reinforced-plastics and decorative laminates' in Jester, T. (Ed.): Twentieth Century Building Materials. McGraw-Hill,New York, November 1995. Walker, A.: 'When the artificial becomes real' in Slatton, D, and Shiffer, R. (Ed.): Preserving the Recent Past. Conference publication, Historic Preservation Education Foundation, Washington,1995. Walker, A.: 'Plastics: the building blocks of the twentieth century', Construction History Journal, 1994, vol. 10, pp.67-88. Anthony Walker is an architect in private practice with a special interest in the conservation of buildings of the 20th century, and in particular the technology and materials of the era including the uses of polymers. As a committee member of the Plastics Historical Society he is responsible for establishing a database of information about plastics and would be pleased to receive information or questions about any significant use in buildings. He can be contacted at his practice Damond lock Grabowski & Partners, 12 Sutton Row London, WlV6AB, ,et: 0171-439 6701 fax 0171-734 1793. IN SEARCHOF CONCEALED TIMBERDECAY Chris Cullen describes methods of searching out the causes of decay EXTENSIVEEXPOSURE Dry rot and death watch beetle are often heralded as the most destructive pests in our historic buildings, but neither causes so much damage as the misguided determination to pursue all evidence of decay ruthlessly to its furthest extent. Fears of extensive concealed damage frequently result in over-zealous exposure work and in some instances the expense of reinstatement can ultimately be so extortionate tl1at finishes may never be replaced. Major recommendations for minor problems not only divert lin1ited resources away from more important conservation repairs, but tl1ecombination of investigation and treatment is commonly more destructive tl1an the problem they are supposed to eradicate. In the last issue of CONTEXT49 Context, Jenny Carllie highlighted just one example of this unfortunately regular trend.* Opinions range from a belief that all timber buried into external walls is bound to be decayed, to convictions that all old timber must be exposed and treated simply because it never has been. Extraordinarily destructive measures are taken to expose tin1ber in order to treat it as a precaution against problems which have never occurred. Conversely, principal structural elements in the vicinity of serious decay may inadvertently not be investigated because the presence of concealed timber is not anticipated. * CARLlLE, J.: 'The curse of the dead death watch beetle', Context 48, December 1995, pp26-27. So how can all the risks be assessed without wholesale stripping out? There is no standard solution, but a pool of techniques is available and with experience these techniques can be adapted to investigate most situations. CONCEALEDCAVITIES It may seem insulting to suggest lifting floor boards or removing access panels, but unfortunately Iso frequently see such tota:ilyinappropriate exposure work that the opportunity clearly needs to be recommended. All too often a hole issmashed· through a damp stained ceiling to avoid awkward, dirtyroofspace access orwhere afloor board could have been lifted above. To lift individual boards rather than to break up the floor is often a skilled task 13
ihbc.org.ukRkJQdWJsaXNoZXIy MjgyMjA=