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
© 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, Australia. email: [email protected]
— ii —
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 outbuildings 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 characteristics) is lost in the process of replacement.2 Thus,
adequate documentation of the status quo is desirable. This brief guide sets out the various parameters 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 material, 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 industry. It has been posited that corrugated iron has a
special place in Australian architecture and aesthetic (Lewis, 1982; Meyers, 1981).
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 colour 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)
During the mid-nineteenth century, galvanisation (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). 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
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, different brands, etc.) indicate changes to the fabric of
the structure such as repair or extensions. Various 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 offered by some manufacturers (e.g. Redcliffe
Crown: Spennemann, 2015c).
particular prefabricated materials, used the Imperial 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 measuring 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, before rolling, was originally 27⅞" wide.5 In consequence, any flattening of the corrugations will
result in an increase in measured width, to a maximum 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 between 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 variations were available in Australia and New Zealand, either as standard stock or as specially ordered imports (Table 1). By far the most commonly occurring corrugation is 3" x ¾". Smaller
corrugations such as 1" x ¼" (commonly called
‘ripple iron’) also exist, frequently used for ceilings and more ornamental coverings.
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), nineteenthand early twenty-century building materials, in
4
5
. At a period of 3" and an amplitude of ¾", the length of the arc is 3.477". 6
. Common sense, however, should prevail, as some roofs will require scaffolding to ensure safe access. . In mathematical terms, the corrugations are of course a sine wave, with an period (=pitch) and an amplitude (=depth). —2—
Dirk HR Spennemann, Techniques in Historic Preservation: Recording Corrugated Iron
Table 1. Corrugation profiles marketed in Australia by
Lysaght Ltd (1916, p. 9)
coating of zinc and silicon (Zincalume, since
1966)(Bluescope, 2014). More recently, corrugated aluminium sheets have come on the market.
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 11
3 /16" 2⅜" weight bearing, standard stock 4" 1" supplied to order 5" 1¼" supplied to order 5" 1½" supplied to order 1
5 /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 common 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 colour 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 installed. While from the late 1880s full rollercoating became more common, many older galvanising 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). 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 onwards, 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 distinguished from iron and steel by using a magnet.
It remains difficult to distinguish sheets of corrugated 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, especially 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 required number of sheets from local retailers or
wholesalers (see for example the pricing
information compiled in Spennemann, 2015c)
—3—
Dirk HR Spennemann, Techniques in Historic Preservation: Recording Corrugated Iron
Table 3. Composition of cases of 26-gauge galvanised corrugated iron (Gemmell Tuckett & Co, 1875, p. 13; Lysaght Ltd,
1897, p. 7; Lysaght Ltd Pty, 1921).
Length 5 ft 6 ft 7 ft 8 ft 9 ft 10ft Redcliffe Crown Lysaght Lysaght 1875 1897 1921 106 115 116 90 96 98 78 82 84 68 72 73 58 64 65 — 57 58 Brand (if bearing maker’s stamp) In many cases galvanised iron, whether corrugated 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 machine.
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 bottle / 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 conditions (see Gerharz, Lantermann, & Spennemann,
1988), which cannot be ensured when recording
galvanised iron stamps in enclosed spaces, especially 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, leading to a flaking loss of pigment.9 This exposes
the underlying substrate of zinc. Over the duration of the paint’s existence, that part of the zinc
covered by paint oxidised, forming zinc hydroxide 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 literature (Branne, 1929, p. 601). This meant, however, 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 corrugationswide side lap added 25% weight to the corrugated 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). —4—
Dirk HR Spennemann, Techniques in Historic Preservation: Recording Corrugated Iron
natingly with the edges of the corrugations pointing down and pointing up.
ing fashion (e.g. NSW Heritage Office, 1998). As
shown elsewhere (Spennemann, 2015e), the
striped appearance is a result of differential corrosion which has nothing do with the method of
galvanisation employed in the manufacture of the
sheets.
Re-­‐use Fig. 7. Methods of overlapping sheets of corrugated iron.
It is frequently asserted that the striped appearance of many historic roofs is caused by unevenly coated sheets which were laid in alternat-
Corrugated galvanised iron was frequently salvaged 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)
—5—
Dirk HR Spennemann, Techniques in Historic Preservation: Recording Corrugated Iron
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 Dimensions Method Measure in inches (cm) with steel tape Thickness Measure in mm with sliding caliper, convert to gauge (Table 2) Measure with ruler & sliding callipers Pitch & depth Use a plasterer’s comb to record at scale 1:1, then measure in office Galvanisation Observation & photography Material Observation & assess flexibil-­‐
ity Brand Photography Colour Makers stamps occur in a number of colours. Original use Arrangement Count Observation & photography Observation Observation Issues to be considered 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) 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 Measurement in mm or inches. Time consuming and error prone (Fig. 16–Fig. 17) Accurate and speedy method (Fig. 18–Fig. 19) It also permits to cross-­‐check profiles while on site Hot-­‐dipped galvanisation shows the characteristic spangle If required, a magnet can be used to distinguish flat sheets of lead flashing from iron flashing 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 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 Look for linear discolourations and nail holes Record nature of overlap (corrugations) Watch out for partial sheets —6—
Dirk HR Spennemann, Techniques in Historic Preservation: Recording Corrugated Iron
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)..
—7—
Dirk HR Spennemann, Techniques in Historic Preservation: Recording Corrugated Iron
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).
—8—
Dirk HR Spennemann, Techniques in Historic Preservation: Recording Corrugated Iron
Bibliography Bluescope. (2014). History of Bluescope Steel. Melbourne:
Bluescope.
Branne, John S. (1929). Roofs and Roof Coverings. In G.
A. Hool & N. C. Johnson (Eds.), Handbook of Building
Construction. Data for a rchitects, dedigning and constructing
engineers,and contractors (2nd ed., Vol. 1, pp. 594–605).
New York: MacGraw -Hill.
Brisbane City Council. (2014). Replacing corrugated iron
roofs. Brisbane: Brisbane City Council.
Brooks, Katherine, & Loveys, Kirsty. (2014). Heritage
Technical Note. Re-Roofing of a Heritage Place –
how do we do it? Adelaide: Adelaide City Council.
Davies, James. (1899). Galvanized Iron. Its manufacture and
uses. A detailed description of this important industry and its
manufacturing process. London & New Yrok: E. & F N
Spon and Spon & Chamberlain.
Duran, Bernado, & Langill, Thomas. (2007). Cleaning wet
storage stain from galvanized surfaces Galvanizing Note.
Process and Design Notes on Hot-Dip Galvanizing.
Centennial, CO: American Galvanizers Association.
GalvInfo Center. (2015). 2. Coating Processes and Surface
Treatments. 2.6. The Spangle on Hot-Dip Galvanized
Steel Sheet GalvInfoNote Durham, NC: International
Zinc Association.
Gemmell Tuckett & Co. (1875, Dec 3). 64 cases galvanized
iron, Argus, p. 2 col. a.
Gerharz, Rudolf R., Lantermann, Renate, & Spennemann,
Dirk H.R. . (1988). Munsell Color Charts: A necessity
for archaeologists? Australian Journal of Historical
Archaeology, 6, 88–95.
Gillette, Halbert Powers. (1907). Handbook of cost data for
contractors and engineers; a reference book giving methods of
construction and actual costs of materials and labor on
numerous engineering works. New York & Chicago:
Myson C Clark Publishing Co.
Globe Iron Roofing and Corrugating Co. (1890).
Illustrated and descriptive catalogue of steel and iron
roofing and corrugated iron. Cincinnati, OH: Globe
Iron Roofing and Corrugating Co.
Heritage Branch [Qld]. (2014). Technical Note. Conserving
Roofs. Brisbane: Heritage Branch, Department of
Environment and Heritage Protection.
Heritage South Australia. (1999). Heritage Conservation
3.10: Early Roofing and Roof Materials in South
Australia. Adelaide: Department for Environment,
Heritage and Aboriginal Affairs.
Heritage Victoria. (2001). Roofing. Corrugated Roofing.
Melbourne: Heritage Victoria.
Lewis, Miles. (1982). The Corrugated Iron Aesthetic.
Historic Environment, 2(1), 50.
Lysaght Ltd, John. (1897). The metal trades' referee and
storekeepers' guide : being a table of weights, measurements, and
other ... useful information. Melbourne: John Lysaght.
Lysaght Ltd, John. (1916). The metal trades' referee : being a
general guide for ironworkers, storekeepers, country residents
&c, containing tables of weights, measurements, average
rainfall, postal and other useful information (9th ed.).
Melbourne: Imperial Press.
Lysaght Ltd Pty, John. (1921). The referee : specially featuring
Lysaght's Newcastle Works, being a general guide for
ironworkers, storekeepers, country residents &c, containing
tables of weights, measurements, average rainfall, postal and
other useful information (12th ed.). Sydney: Imperial Press.
McM, D. (1946). Corrugated Iron Encyclopedia Britannica
(32nd ed., Vol. 6 Pt 1 Colebrooke-Damascius).
Oxford: Encyclopedia Britannica.
Meyers, Peter. (1981). Corrugated Galvanised Iron: The
Profile of a National Culture? Transition(June), 24.
Munsell Color. (1990). The Munsell book of color : removable
samples in two binders. New Windsor, NY: Macbeth
Division of Kollmorgen Instruments.
Munsell Color. (2008). The Munsell book of color : removable
samples in two binders. Grand Rapids, MI.: Munsell Color
Services.
NSW Heritage Office. (1998). Information Sheet 4.1
Corrugated Roofing. Sydney: NSW Heritage Office.
Orrcon Steel. (2005). How to Prevent White Rust on Zinc
Coated Steel Products. Brisbane: Orrcon Steel.
Palmer, Henry Robinson. (1829). United Kingdom Patent
No. 5786. B. P. Office.
Pöll, J. S. . (1999). Historical Note. The story of the gauge.
Anaesthesia, 54, 575–581.
Spennemann, Dirk HR. (2015a). Callitris and Mud. An
Analysis of the Construction and Decay of a German
Farmhouse Complex at Edgehill near Henty (NSW)
Institute for Land, Water and Society Report (Vol. 86).
Albury, NSW: Institute for Land, Water and Society,
Charles Sturt University.
Spennemann, Dirk HR. (2015b). Galvanised Iron at Old
Urangeline Station, near Rand (NSW). Photographic
Documentation and Analysis Institute for Land, Water
and Society Report (Vol. 91). Albury, NSW: Institute for
Land, Water and Society, Charles Sturt University.
Spennemann, Dirk HR. (2015c). Redcliffe Crown
Corrugated Iron in Australasia. A survey of its history,
marketing and distribution, 1875–1921 Institute for
Land, Water and Society Report (Vol. 90). Albury, NSW:
Institute for Land, Water and Society, Charles Sturt
University.
Spennemann, Dirk HR. (2015d). Techniques in Historic
Preservation: Recording Corrugated Iron. Albury,
NSW: Institute for Land, Water and Society, Charles
Sturt University [DOI 10.13140/RG.2.1.4212.2727].
Spennemann, Dirk HR. (2015e). Techniques in Historic
Preservation: Why do corroded corrugated iron roofs
have a striped appearance ? Albury, NSW: Institute for
Land, Water and Society, Charles Sturt University.
WA State Heritage Office. (2013). Policy for Corrugated
Metal Roofs. Perth: Heritage Council and State
Heritage Office of Western Australia.
—9—