historic scotland inform guide - care and maintenance of corrugated iron

Care and Maintenance of Corrugated Iron Principal author: David S Mitchell Published by echnical Conservation, Research and Education Group, May 2008 Historic Scotland, Longmore House, Salisbury Place, Edinburgh EH91SH el: 0131 668 8638 Fax: 0131 668 8669 www.historic-scotland.g ov.uk email:[email protected] .uk T e H o u s e 0 5 / 0 8 P r o d u c e d f r o m s u s t a i n a b l e m a t e r i a l Maintenance Issues Corrugatedironbuildingsare particularl y susceptible to damage rom grass or other build up o soil / garden vegetation growing against the sheets and trapping moisture which accelerates corrosion . A sound understanding o the building is required. Entirely preabricated buildings may have a visible manuacturers nameplate which could lead to a search o archive catalogues or reerencing. Cleaning gutters and general maintenance is particularly required with corrugated iron structures as decay can happen quickly. Groundwater splashing onto walls also accelerates decay. Junction details, where ventilators and windows etc. have been inserted are problem areas. A good seal is dicult to achieve in the original construction and associated sealing materials oten break down and do not perorm eectively Corrugated iron roos may also be ound to overlie relatively intact thatch, retained or the insulation it provides, or an intact traditional cruck rame – both worthy o preservation. Corrugated iron has been the saviour o many vernacular buildings. Corrosion Since all metals corrode, the primary problem in dealing with corrugated iron is attempting to slow down the rate o corrosion. Corrosion can lead to coating loss, loss o structural strength or integrity, and serious corrosio n o the iron can lead to the complete loss o the sheets. Since the sheets are not permeable to moisture, condensation is a problem, and wetting and drying cycles remain the primary cause o decay – internally and externally. Te quality o early galvanising was variable. Tis oten ails, resulting in an oxidised surace (rusted appearance) which is aesthetically pleasing or many due to its natural colouration. In many cases the rusted roos are seen as an integral part o the rural landscape. Rainwater run oover the rusty sheets onto masonry can be a problem. Where exposed stone is marked in this way the staining is virtually impossible to remove. Coating Failure Coating ailure is common on galvanised suraces. Eective coating requires the use o a mordant wash to provide a chemical etch or the primer layer, or the use o an etching primer or galvanised suraces. Oten, neither was used. Although there are some rms still making corrugated iron sheets it is important to retain the original sheets as, in many cases, the matching proles and sizes may be no longer available. It is technicall y easible to re-galvanis e existing sheets, and to patch repair them in some cases, although the thin gauge o metal makes this dicult to achieve. It is inadvisable to install new sheets directly on top o existing corroding sheets. Tis will trap moisture, and accelerate corrosion o the new sheet by creating a corrosion cell. Moisture movement and entrapment by capillary action between the sheets is also likely. Accelerate d corrosion by overlaying sheets and causing capillary action Any repairs should ollow the philosophy o the minimum intervention necessa ry to reduce the loss o historic material. Wholesale dismantling may be required or ull repairs, and the services o an experienced proessional should be sought to ensure that this does not place undue stress on other components. Firms experienced in the repair o traditional ironwork should be employed, but it should be appreciated that ew will have experience o working with corrugated iron. Sheet metal workers who are sympathetic to the historic qualities o the material and posses a knowledge o how it perorms may also be considered. Painting Over painting sheets should ollow traditional practice. It may be possible to identiy the original paint on existing ironwork and other local examples might provide an indication o the original colour. Te use o red lead or roos and walls was common. Tis material is still available and its use does not require statutory consent to use. Green and red colours were airly commonly applied, as were creams and browns in the twentieth century. Further reading and inormation Scotland’s Listed Buildings: What Listing Means to Owners and Occupiers, Historic Scotland (2006) Free publication http://historic-scotland.gov.uk/index/ publications/pubsorowners.htm Te Scottish Ironwork Foundation Visit http://www.scottishironwork.org INFORM; Boundary Ironwor k – A guide to re-instatement INFORM; Iron Gates and Railings HistoricScotland,2005 echnical Advice Note 29 – Corrugated Iron and Other Ferrous Cladding HistoricScotland,2004 Ashurst, J and Ashurst N, 1988, Practical BuildingConservation;EnglishHeritage echnical Handbook. Vol. 4. Metals, Aldershot; Gower echnical Press Useul contacts Historic Scotland, Longmore House, Salisbury Place, Edinburgh, EH9 1SH 0131 668 8600 www.historic-scotland.gov.uk Historic Scotland echnical Conservation ResearchandEducation, Conservation Bureau & echnical Enquiry Service, 0131 668 8668 [email protected] Historic Scotland CRE Resource Centre. 0131 668 8642 [email protected] Historic Scotland CRE Publications Department 0131 668 8638 Historic Scotland Investments and Projects eam: 0131 668 8801: Fax - 0131 668 8788 [email protected] Historic Scotland Inspectorate: [email protected] Materials Corrugated iron was patented in 1828 with corrugatio ns made in fat iron sheets by passing the thin plates through rollers to provide rigidity and additional structural strength. Until the 1920s corrugated sheets were manuactured by a broad range o ironworkers in various lengths, usually up to a maximum o ten eet. Sheet thickness varied rom around 0.5mm to 1.5mm depending on the application. Galvanisi ng o the iron with zinc became increasingl y common at the end o the 19th century. Sheet pitch and profles A wide variety o pitches was available, with standard dimensions varying rom 25 – 153mm. For domestic purposes, a 76mm (3 inch) pitch was common. A range o proles were manuactured, with rms such as FW Braby developing their own branded lines. Coatings A range o coatings was employed to protect corrugated iron rom the elements. Oil (usually linseed) based paints were used extensively in conjuncti on with red lead paint, with pitch and bitumen to a lesser extent. Te galvanisin g process involved the iron sheet being dipped into a bath o molten zinc to orm a protective layer on the metal surace. Te zinc coating chemically protected the iron rom corrosion. Tere were a number o patented ‘rustless coatings ’ developed in the late nineteenth and early twentieth centuries then ormed protective oxide layers on the surace o the metal and were oten known as the Barprocess ater the inventor. Introduction With a pedigree of almost two hundred years corrugated iron is a much undervalued material that was used extensively in traditional construction . Te material is relatively light, portable and its adaptability means that it was often used to replace or cover a thatch roof, or construct a large agricultural or industrial building. Tis INFORM provides some historical background, and addresses the physical properties of the material and its uses. It also covers the conservation, repair and maintenance of corrugated iron in a variety of situations. Te architectural iron industry in Scotland was world leading at the end o the 19th century, and corruga ted iron was extensively used as a construction material. Scottish rms such as Robertson and Lister, AJ Main, and William Bain and Co developed their specialism in the manuacture o iron building components and entire buildings using corrugated iron. Construction details and techniques Supplied in a range o sizes and proles corrugated iron was requently used or roong and walling, and to a lesser extent or encing and other innovativeuses. Manuacturersquicklydeveloped other components that allowed them to construct a building rom a rame and corrugated sheet. Tis included ridging details, ventilators and windows. Te retention o these pieces is especially important as most cannot be sourced now. Specialist xings were required to suit the corrugated sheets, including hooks and bolts (usually galvanised) with specially shaped washers with which to eect watertight seals – particularl y on varying proles. Where these remain, they should be careully saved, cleaned and set aside or reuse. In a preabricated structure the corrugated sheets were secured to an internal timber or metal rame. Tis was either let as a nished building i or agricultural use, or or domestic needs internally insulated and covered in timber lining or plaster. Te sheet corrugations lend themselves well to lap joints, oten overlapping by 150mm and by 1- 2 corrugations where sheets are adjacent. As condensation was a major issue perorated sheets were also developed. Portable farm worker shed Galvanisedcorrugatedunclimablefencing.

historic scotland inform guide - care and maintenance of corrugated iron

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