Corrugated iron is a widely used building material whose importance is rarely acknowledged. It is used in all climates, all terrains, is cheap and easily fabricated into all sorts of buildings, and can probably claim to shelter more people from the elements than any other building material. Corrugated iron, often incorrectly called “tin,” is usually coated with zinc so terms such as “corrugated galvanized iron” (CGI), “galvanized iron,” or even “galvo” are often used. But like all great inventions, it has evolved over time, so we now have coatings such as zincaluminium and zinc-aluminium-magnesium, along with special durable organic coatings providing a wide range of colors. The durability of the new products has improved so much that it is the fasteners, not the sheeting, that often break down first. But regardless of the coating, this simple material made of a thin sheet of steel, crinkled for strength and rigidity, then provided with a suitable protective coating, has contributed to the development of farming, light industry, housing, and many other fields of human endeavor like no other building material.
Today, corrugated metal sheets are made by a roll-forming process where wavy rolls press the sheets to give the desired corrugations. The sheets are then cut to the desired length. Rolling and coating are now a completely mechanized process. The corrugations provide greatly increased stiffness and rigidity compared to flat sheets along their length, but also give the ability to be shaped into curved forms. The pitch or distance between corrugations determines the strength, with the lowest pitch (“ripple iron”) having the lowest strength and generally only used for internal applications. A number of new profiles have been introduced in recent years, providing a range of architectural options.
The first patent for “indented or corrugated metallic sheets” was granted to Henry Palmer of the London Dock Co. in 1829. The company purchased flat Corrugated iron can provide an artistic and rustic appearance, as well as protection from the elements. wrought iron sheet, rolled it to shape using fluted rollers, and a year later the first building roofed with this material was constructed at the London docks. The roofing was an immediate success and railway stations, markets, and other large-span enclosures in England were soon roofed. These first examples were protected with a thin layer of paint, which provided limited protection from corrosive smoke, steam, and salt air. The problem was addressed by Stanislaus Sorrel, a French civil engineer, who in 1837 patented a process of coating iron with a thin coat of zinc, although the sheeting was still often painted for decorative purposes.
By the 1850s, mass production and increased competition led to more widespread use of the material. The gold rushes in California and Australia in the 1850s led to a market in pre-fabricated buildings that would be lightweight and quick and easy to erect. Corrugated iron formed the basis of the first flat-pack industry. Even after the gold rushes subsided, corrugated iron remained an ideal building material in remote areas and by the outbreak of the First World War, it was a common feature of rural landscapes around the world. But it was also widely used in built-up regions in domestic, commercial, and industrial applications.
By this time, steel had replaced wrought iron as the base material and it had become cheaper. War brought perhaps the most famous corrugated iron building, the semi-circular Nissen hut and its American version, the Quonset hut, where the lightness, ease of transport, and erection made them a great success with the military forces. In recent years, the product has managed to shake off its rather utilitarian image through the work of a number of imaginative architects who have used it to produce buildings of elegance and style that fit in well with the local landscape.
If corrugated iron has been important in the developed West, then it is almost a currency in the developing world. Since the Second World War, informal communities with populations of a few hundred to a million or so have sprung up on the periphery of urban centers in Africa, Latin America, and South Asia. Without land title or money, the residents have adopted corrugated metal as a flexible, cheap, and easy-to-work-with building material. It is suited to hot and temperate climates, it can withstand monsoon rains, and is rot-proof. It can be easily erected and pulled down, and when no longer needed for housing, it can be used for channelling water, and covering muddy paths or an animal enclosure.
Corrugated iron has been and continues to be an invaluable building material that deserves to be taken seriously. It shows that steel can be simply and cheaply formed to a useful shape, protected from corrosion by a range of coatings, and made accessible to citizens in all corners of the globe. But for heavy steel sections in severe environments, other coatings such as inorganic zinc silicate, discussed next month, are needed.
Further reading: Adam Mornement & Simon Holloway, Corrugated Iron: Building on the Frontier, Frances Lincoln Ltd. (2007).