Traditionally, the term ‘street furniture’ would be associated with benches manufactured with a cast iron frame. Although the variety of design and manufacture of street furniture has greatly improved over time, cast iron is still used extensively for benches and seating. This article will take a closer look at this metal specifically focusing on its sustainability.
Records show that cast iron was first discovered and used by the Chinese in the 5th Century BC. Since then, humans have relied on its characteristics up until the current day. Although it has been superseded by steel since the 1950’s it is still used today for a limited number of applications, including benches.
Cast Iron is mainly iron, but it is also alloyed, or mixed with carbon. Carbon typically makes up 2% – 4% of the overall metal. This high carbon content gives iron its rough and bumpy feel, but also makes it more brittle than steel and stainless steel.
It will readily rust due to the high amount of carbon present within the metal.
The reason it is called cast iron and not simply iron is because it is very runny when it is molten and does not shrink much when it solidifies, which makes it ideal for making castings. This is partly why it is popular for benches and seating because it is easy to form into intricate shapes and patterns – the alternative, laser cutting steel, is much more difficult and therefore, more expensive.
The main difference between iron and steel is the carbon content. As mentioned earlier in this article, cast iron has a 2% – 4% carbon content whereas steel has a 0.1% – 0.5% carbon content. Stainless steel is like steel in terms of carbon content, but it is alloyed with chromium which makes stainless steel resistant to rust.
Cast Iron is the closest metal to iron ore that is mined from the earth in terms of how much processing is needed to transform the mined iron ore into the finished product. Steel and stainless steel are also manufactured from iron ore, but they have to go through additional processes to lower the carbon content and introduce alloyed elements.
1, Traditionally, 90% of benches were manufactured with a iron frame. This proportion has now almost completely reversed to 10%, especially for private projects. Steel is the material that has superseded iron.
Over the last 10/20 years, seating designs have become more minimalistic and less ornate, which suits steel because it is much stronger in thinner profiles, whereas iron is very brittle. Also cast iron is much easier to cast, but as designs are less ornate there is no need for complex casting which works in steels’ favour.
2, The second option is timber. Although timber can be incorporated into a mixed timber/metal bench, there are all-timber seating options available such as Logic’s Pueblo and Union Styles. Although it is very difficult to create intricate designs with timber, it scores highly for sustainability.
Iron and steel uses vast amounts of energy to produce and cannot be considered a sustainable material. In fact, one blast furnace (used in the manufacture of iron/steel) consumes as much energy as a town of 100,000 people.
Timber is much more sustainable as the only energy needed will be the transportation carbon footprint – transporting it from the forest to the end destination. The other problem is the potential for causing deforestation. This risk can be eliminated by selecting UK grown timber. Any UK grown timber felled will always be replenished thanks to the UK forestry commission’s regulations, and there is the added benefit of having a very limited transport carbon footprint (assuming the timber would be used in the UK).
In conclusion, cast iron is not suitable for most benches and seating manufactured today because it is very brittle which makes it impossible to use in many designs. Steel is a better option when looking at material properties.
However, neither steel or cast iron can be considered sustainable so every effort should be made to use UK grown timber, which, in our opinion, is the most sustainable material for manufacturing outdoor benches and seating.