Recording Historic Corrugated Iron...Recording Historic Corrugated Iron A Guide to Techniques Dirk...

Recording Historic Corrugated Iron A Guide to Techniques

Dirk HR Spennemann

Techniques in Historic Preservation

Recording Historic Corrugated Iron A Guide to Techniques

Dirk HR Spennemann

Albury October 2015

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© 2015. All rights reserved. The contents of this publication are copyright in all countries subscribing to the Berne Convention. No parts of this report may be reproduced in any form or by any means, electronic or mechanical, in existence or to be invented, including photocopying, recording or by any information storage and retrieval system, without the written permission of the authors, except where permitted by law. Cover: Photograph © Dirk HR Spennemann 2015 Preferred citation of this Report Spennemann, Dirk HR (2015) Techniques in Historic Preservation: Recording Historic Corrugated Iron. A Guide to Techniques. Second, enlarged edition. Institute for Land, Water and Society Report nº 92. Albury, NSW: Institute for Land, Water and Society, Charles Sturt University. ii, 9pp; ISBN 978-1-86-467275-6

Disclaimer The views expressed in this report are solely the author’s and do not necessarily reflect the views of Charles Sturt University.

Contact Associate Professor Dirk HR Spennemann, MA, PhD, MICOMOS, APF Institute for Land, Water and Society, Charles Sturt University, PO Box 789, Albury NSW 2640, Aus-tralia. email: [email protected]

Introduction Corrugated iron roofs of many nineteenth and early twentieth century properties are nearing the end of their life due to progressing decay and are in in need of conservation management actions. The same applies to corrugated iron-clad out-buildings on many farms.

Very often, the corrugated iron sheets have decayed to such a degree that they are in need of full replacement if water tightness of the roof is to be maintained.1 One of the concerns is that the historic information contained in original sheets (via their brand and physical characteris-tics) is lost in the process of replacement.2 Thus, adequate documentation of the status quo is desir-able. This brief guide sets out the various param-eters that should be recorded when documenting structures with historic corrugated iron.3

Corrugated Iron Corrugated iron, i.e. flat sheet-iron that has been cold rolled into a wavy surface, was first patented in the United Kingdom in 1829 (Palmer, 1829). Many manufacturers quickly offered the product once the original patent had run out in 1843. By the 1850s the use of corrugated iron had become wide-spread; it served mainly as a roofing materi-al, given the structural strength it provides along the long axis of the corrugations. Subsequently, Australia became the premier export market for the British corrugated and galvanised iron indus-try. It has been posited that corrugated iron has a special place in Australian architecture and aes-thetic (Lewis, 1982; Meyers, 1981).

During the mid-nineteenth century, galva-nisation (the application of zinc on ferrous met- 1 . For this a number of publications have been produced by

the various state heritage offices (Heritage Branch [Qld], 2014; Heritage South Australia, 1999; Heritage Victoria, 2001; NSW Heritage Office, 1998; WA State Heritage Of-‐fice, 2013) as well as guidelines by local councils (Brisbane City Council, 2014; Brooks & Loveys, 2014)

2 . For an example for the wide range of galvanized iron brands used in a single farm complex, see Spennemann (2015b)

An assessment of the history, marketing and distribution of single brand of corrugated iron (Redcliffe Crown, 1875–1921) showed that several occurrences had been replaced since they had been reported in the literature. As result, it was impossible to verify the variation of the stamp that had been used (Spennemann, 2015c).

3 . This document is a revised and substantially enlarged ver-‐sion of an earlier guide (Spennemann, 2015d).

als) became a wide spread method of slowing down the corrosion of products made from sheet iron. The common process until the end of the nineteenth century was to first hand-dip and later machine-dip the iron sheets in a pot of molten zinc (at about 450°C) (Davies, 1899, p. 60ff). Hot-dipped galvanised iron shows a surface col-our with a characteristic broken pattern, the ‘spangle’ (GalvInfo Center, 2015). In 1888 John Lysaght Ltd developed a four-roll galvanising machine which ensured an even coating and thus provided reliable quality, while at the same time saving on zinc. Galvanised iron produced by this process shows a homogenous surface colour.

Fig. 1. Typical decaying farm building with corrugated iron

roof and collapsed verandah (Klemke’s Farm, Edgehill, NSW) (Spennemann, 2015a)

Fig. 2. Typical decaying farm building with corrugated iron used for walls and roof (stables, racecourse, Albury, NSW).

The period between 1894-1895 were the transition years from puddled (and thus soft) iron to steel in the sheet metal trade. While some companies adapted, others failed to modernise and continued to use puddled iron; eventually the latter companies went out of business (e.g. Redcliffe Crown: Spennemann, 2015c).

Dirk HR Spennemann, Techniques in Historic Preservation: Recording Corrugated Iron

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Documentation Criteria and Techniques Care should be taken to investigate all sheets that can be accessed and assessed.4 Changes in the type of the sheets (marked vs. unmarked, differ-ent brands, etc.) indicate changes to the fabric of the structure such as repair or extensions. Vari-ous characteristics of the corrugated iron sheets need to be documented (Table 4).

Dimensions, length and width Historically, corrugated iron tended to be sold in lengths of five to ten feet, even though longer sheets were technically possible (depending on the side of the dipping vats) and were indeed of-fered by some manufacturers (e.g. Redcliffe Crown: Spennemann, 2015c).

Fig. 3. Standard nine-foot sheet of corrugated iron.

Note that part of the corrugations have been flattened. (Edgehill, NSW)(Spennemann, 2015a)

Even though the currently accepted mode of documentation is to record all measurements in the International System of Units, that is using the metre scale (and its derivatives), nineteenth- and early twenty-century building materials, in

4 . Common sense, however, should prevail, as some roofs

will require scaffolding to ensure safe access.

particular prefabricated materials, used the Impe-rial scale (feet, inches, gauge). Thus it is desirable to record the dimensions either in both metric and Imperial, or in Imperial alone.

Care needs to be exercised when measur-ing partially flattened sheets of corrugated iron. For example, a standard sheet (Fig. 3) showing eight corrugations, has a width of 24" if the pitch is 3" (standard pitch). A standard corrugation depth of ¾" implies that the flat metal sheet, be-fore rolling, was originally 27⅞" wide.5 In conse-quence, any flattening of the corrugations will result in an increase in measured width, to a max-imum of 27⅞".

Pitch and depth of the corrugations The corrugations are commonly described in terms of pitch, i.e. the distance between two crests, and depth, i.e. the vertical distance be-tween the top of the rise and the bottom of the valley (Fig. 4).6

Fig. 4. Corrugated iron. Definition of terms.

During the nineteenth and early twentieth century a wide range of pitch and depth varia-tions were available in Australia and New Zea-land, either as standard stock or as specially or-dered imports (Table 1). By far the most com-monly occurring corrugation is 3" x ¾". Smaller corrugations such as 1" x ¼" (commonly called ‘ripple iron’) also exist, frequently used for ceil-ings and more ornamental coverings.

5 . At a period of 3" and an amplitude of ¾", the length of the

arc is 3.477". 6 . In mathematical terms, the corrugations are of course a

sine wave, with an period (=pitch) and an amplitude (=depth).


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Table 1. Corrugation profiles marketed in Australia by Lysaght Ltd (1916, p. 9)

Pitch Depth availability in 1916 ½" ⅛" standard stock 1" ¼" standard stock 1½" ⅜" supplied to order 2" ½" supplied to order 2½" ⅝" supplied to order 3" ¾" standard stock

311/16" 2⅜" weight bearing, standard stock 4" 1" supplied to order 5" 1¼" supplied to order 5" 1½" supplied to order

51/10" 1" supplied to order 6" 1½" supplied to order

Thickness Nineteenth century sources refer to the thickness of iron as expressed in ‘gauge.’ The most com-mon type of iron was 24- and 26-gauge.7 In the absence of commonly accessible sliding callipers that measure in gauge, it is advisable to record the thickness in millimetres and then to convert the measurements. Table 2 provides a conversion of millimetres to gauge.

Table 2. Conversion of gauge (thickness) to mm and inches

Gauge mm inch 18 1.245 .049 20 .889 .035 22 .711 .028 24 .559 .022 26 .457 .018 28 .356 .014

Nature of galvanisation Hot-dipped galvanised iron shows a surface col-our with a characteristic broken pattern, the ‘spangle’ (Fig. 5, left). Iron galvanised by rollers has a more uniform coating (Fig. 5, right). Hot dipping was the sole technique available until the late 1880s, with some vats having rollers in-stalled. While from the late 1880s full roller-coating became more common, many older gal-vanising plants continued to hot-dip until well after World War I.

Other methods of galvanisation are more recent, such as colour-painted coating of zinc and aluminium (Colorbond, since 1966) and a

7 The gauge used was the Birmingham wire gauge. For the

historic context of the gauge, see Pöll (1999).

coating of zinc and silicon (Zincalume, since 1966)(Bluescope, 2014). More recently, corrugat-ed aluminium sheets have come on the market.

Fig. 5. Comparison of hot-dipped (left) and rolled galvanised

iron. Note the pronounced ‘spangle’ of the hot-dipped iron

Material (puddled iron, steel) The early iron sheets consisted of wrought iron manufactured in the puddling process, which resulted in iron bars with a range of impurities. The iron was then rolled flat into sheets in rolling mills and cut to length. From the mid-1890s on-wards, steel was used as the base of corrugated iron sheets. In addition, corrugated sheets can also be made from re-rolled tin (very rare) and in particular Zincalume.

Zincalume and rolled tin can be readily dis-tinguished from iron and steel by using a magnet. It remains difficult to distinguish sheets of corru-gated steel from sheets of corrugated puddled iron. The latter tends to be softer and thus more flexible (at the same gauge), but this is difficult to ascertain without comparison specimens, espe-cially when the iron is still in situ, such as on a roof.

Quantity of Sheets It is advisable to count out the number of sheets used on a roof or structure. The number of sheets can then be correlated with the number of cases that would have been required (Table 3). It can be surmised that stations, with their diverse demands, may have bought corrugated iron by the case rather than as individual sheets. Owners of urban properties may have acquired the re-quired number of sheets from local retailers or wholesalers (see for example the pricing information compiled in Spennemann, 2015c)


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Table 3. Composition of cases of 26-gauge galvanised corrugat-ed iron (Gemmell Tuckett & Co, 1875, p. 13; Lysaght Ltd,

1897, p. 7; Lysaght Ltd Pty, 1921).

Length Redcliffe Crown

1875 Lysaght 1897

Lysaght 1921

5 ft 106 115 116 6 ft 90 96 98 7 ft 78 82 84 8 ft 68 72 73 9 ft 58 64 65 10ft — 57 58

Brand (if bearing maker’s stamp) In many cases galvanised iron, whether corrugat-ed or flat, was marked with a brand or maker’s stamp (Fig. 10–Fig. 14). That paint stamp, either a rubber stamp or a stencil, was applied before the sheet was run through a corrugation ma-chine.

Over time the stamps tend to bleach, caused both by a decay of the paint and due to physical weathering.8 An option is to moisten the surface of the stamp with a hand-held spray bot-tle / flower mister (Fig. 6).

Fig. 6. Wetting the surfaces with a hand-held spray bottle can

enhance the recognition of detail.

Ideally, all stamps are photographically recorded as detailed assessments have shown a variability among the impressions, even of the same batch (Fig. 9).

Colour of the stamp While it may be tempting to accurately record the colour of a stamp using Munsell Color Charts (Munsell Color, 1990, 2008), both practical and

8 . In contrast, stamps on the (protected) underside of the

sheet often appear almost ‘new.’

preservation issues counsel against doing so. For one, to accurately record the colour of each stamp will be very time consuming; as most stamps in situ may be difficult to access in a safe manner without scaffolding. Secondly, accurate colour recording requires uniform light condi-tions (see Gerharz, Lantermann, & Spennemann, 1988), which cannot be ensured when recording galvanised iron stamps in enclosed spaces, espe-cially roof cavities.

The primary argument against recording colour, however, is that the colour of a stamp changes. Fig 8 shows three examples of Braby’s Sun Barn stencils, all from the same roof of the woolshed at Old Urangeline Station (Spennemann, 2015b). The stencil’s paint decays with a break-down of the oil-based binder, lead-ing to a flaking loss of pigment.9 This exposes the underlying substrate of zinc. Over the dura-tion of the paint’s existence, that part of the zinc covered by paint oxidised, forming zinc hydrox-ide and zinc oxide (‘white rust’, Duran & Langill, 2007; Orrcon Steel, 2005).

Arrangement Pattern The historic building literature discusses a variety of methods to overlap the sheets of corrugated iron. A six-inch long end overlap, and a single- (Globe Iron Roofing and Corrugating Co, 1890; McM, 1946, p. 32) or double-corrugation side lap is recommended in the historic construction lit-erature (Branne, 1929, p. 601). This meant, how-ever, that when covering a roof with 26" wide sheets, and a double corrugation side overlap, the sheets only yielded an actual coverage of 24". In addition, a 6-inch end lap and 2 corrugations-wide side lap added 25% weight to the corrugat-ed iron sheeting resting on the roof trusses (Gillette, 1907, p. 531).

Many farmers and other builders chose to maximise the coverage at the expense of strength. The method covering the largest area with the smallest number of sheets is the half-lap (Fig. 7). This entails that the sheets are laid alter-

9. Zinc-‐rich coatings of iron, including hot-‐dip galvanisation,

are alkaline in nature. Oil-‐based paints react with the alka-‐line surface, leading to a decay of the binder (saponifica-‐tion).


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natingly with the edges of the corrugations point-ing down and pointing up.

Fig. 7. Methods of overlapping sheets of corrugated iron.

It is frequently asserted that the striped ap-pearance of many historic roofs is caused by un-evenly coated sheets which were laid in alternat-

ing fashion (e.g. NSW Heritage Office, 1998). As shown elsewhere (Spennemann, 2015e), the striped appearance is a result of differential cor-rosion which has nothing do with the method of galvanisation employed in the manufacture of the sheets.

Re-‐use Corrugated galvanised iron was frequently sal-vaged from dilapidated buildings and reused. This is particularly the case in rural support buildings, such as sheds and barns which were often adapted to changing needs. While repairs and the insertion of individual sheets tends to be obvious (Fig. 20), wholesale re-use of sheets may be less easy to detect, especially if the sheets are replaced exactly as they were. Tell tale signs are linear discolourations, where the sheet had once been in contact with the batten of a previous roof, as well as nail / screw holes that do not match up with the battens of the current roof (Fig. 21).

Fig 8. Example of paint decay on sheets of Braby Sun Brand corrugated iron. Woolshed, Old Urangeline Station near Rand (NSW) (Spennemann, 2015b)


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fat standard faint

Fig. 9. Variability of impressions of a Redcliffe Crown stamp on corrugated iron sheets. All sheets come from the same batch. Station Cook House, Old Urangeline Station near Rand (NSW) (Spennemann, 2015b).

Table 4. Documentation criteria, techniques and issues

Criterion Method Issues to be considered Dimensions Measure in inches (cm) with

steel tape Measurement to mm may be too accurate, as original sheets were cut to foot length with some margin. In addition edge corrosion oc-‐curs (Fig. 14)

Thickness Measure in mm with sliding caliper, convert to gauge (Table 2)

Edge thickness may vary due to corrosion, it is recommended to use a ‘clean edge’ (preferably the covered lip) and to take several meas-‐urements. Given the relative thinness of the iron, minor amount of dirt or corro-‐sion deposits (of the zinc) may mask the small variations between gauges (essentially 0.1 to 0.15 mm); it is advisable to brush the edge to be measured, or to rub both sides with a cloth

Pitch & depth

Measure with ruler & sliding callipers

Measurement in mm or inches. Time consuming and error prone (Fig. 16–Fig. 17)

Use a plasterer’s comb to record at scale 1:1, then measure in office

Accurate and speedy method (Fig. 18–Fig. 19) It also permits to cross-‐check profiles while on site

Galvanisation Observation & photography Hot-‐dipped galvanisation shows the characteristic spangle Material Observation & assess flexibil-‐

ity If required, a magnet can be used to distinguish flat sheets of lead flashing from iron flashing

Brand Photography Washed out / faded stamps may require moistening with a hand-‐held spray bottle. —Images may benefit digital post-‐processing /enhancement (contrast and levels). Marks may be partial (when flat sheets are cut for spouting and flash-‐ing)(Fig. 13). Use flash in (partial) sunlight, if the corrugations cast shadows

Colour Makers stamps occur in a number of colours.

Variations in colour have been observed. Some of these may be due to different colour (hues) used in the original stamp, while others are due to paint decay

Original use Observation & photography Look for linear discolourations and nail holes Arrangement Observation Record nature of overlap (corrugations) Count Observation Watch out for partial sheets


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Fig. 10. The maker’s marks can be hidden. Fig. 11. The maker’s marks can be hidden.

Fig. 12. The maker’s marks may be complete

(Spennemann, 2015c). Fig. 13. The maker’s marks may be incomplete

(Spennemann, 2015a).

Fig. 14. The maker’s marks can be faint

(Spennemann, 2015a). Fig. 15. Corroded edges may impair accurate measurements

(Spennemann, 2015a)..


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Fig. 16. Measuring pitch with ruler. Fig. 17. Measuring depth with callipers.

Fig. 18. Using a plasterer’s comb to take off the corrugation at a

scale of 1:1. Fig. 19. Recording the corrugation at a scale of 1:1 for later

accurate measurement.

Fig. 20. Evidence of patching a roof with different sheets. (Spennemann, 2015b).

Fig. 21. The discolouration, as well as the nail holes show that this sheet has been salvaged from elsewhere and reused.

(Spennemann, 2015b).


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