News: Specifying Architectural Cast Iron - a Guide

14 September 2013

The cast iron columns at Gridiron, One Pancras Square, the new flagship building by David Chipperfield Architects designed for Kings Cross, were cast at Hargreaves Foundry in Halifax. We have produced this guide for architects and specifiers to learn more about the project from a specification point of view, to help you consider whether to use architectural cast iron in your project.

We investigate the product in terms of:

  1. Aesthetics
  2. Performance
  3. Cost, and
  4. The Design Process.

We’ve also included images and video about the Cast Iron Columns at Kings Cross.

Aesthetics

Sample Cast Iron Column at Kings Cross

Cast iron is an extremely tactile material. Formed in a casting process where a liquid is solidified in a sand mould, each column surface is slightly different, with minor variations that add to the appeal. No other material has this kind of tactile appeal; the sample column at One Pancras Square has been very popular with the public. The columns have a woven pattern finish, designed by project architect Mathias Kunz.

What can be Cast in Iron?

Cast Iron is an extremely flexible material, and there are very few limitations on size of casting. The 396 columns at One Pancras Square weigh up to 2.2 tonnes each but Hargreaves Foundry can cast items up to 15 tonnes in weight. The columns on the ground floor, the first to be installed, are approximately 6m, twice the height of the columns on the upper storeys which will be 3.25m tall. Castings can be large or small, simple or more decorative, such as intricate balustrades or incised panels. The only limitations are cost, transportation sizes and process complexity.

What Finishes are Available for Cast Iron?

Most cast iron is painted to prevent corrosion. Traditionally castings were painted black as there wasn’t really much choice. Today you can use most of the different types of paint on cast iron and the full range of RAL colours is available. The type and colour of the paint is entirely down to customer choice and should be determined by the conditions of use, ease of access and surface finish.

So, for example, a casting in a difficult to reach location will require a long lasting, low maintenance finish. Alternatively a small, easy to access casting can be touched up easily and often. The casting may have fine detail that would be lost with paint that requires thicker application. All or any these factors could affect customers’ choice and we are always happy to offer advice and guidance.

The columns for One Pancras Square were blasted and then painted with an epoxy zinc phosphate primer and an epoxy glass flake bi-polyurethane top coat by specialist coating contractor CSL Industrial Ltd. This finish was then guaranteed for 25 years. If painting is not to be carried out immediately after manufacture, Hargreaves Foundry can prime their castings if customers choose. This will prevent corrosion in transit.

Antony Gormley Bollards

Some castings are not painted, for example the range of bollards designed by Antony Gormley [pictured] is designed to rust naturally. Find out more about the Antony Gormley bollards here

Performance

Lifespan of Cast Iron

Cast Iron has a long history as a construction material, so its longevity has been clearly demonstrated. The foundry recently replaced some cast iron gutters that were 150 years old. Unpainted, cast iron should be expected to rust at 1/1000th of an inch per year, so even Gormley’s bollards have an extremely long life expectancy.

Responsible Sourcing of Materials

The cast iron produced by Hargreaves Foundry is entirely sourced in the UK from scrap car parts, existing cast iron items and internal returns. As a result the supply chain for cast iron is very short and entirely predictable. Compared to stone or steel sourced overseas, as a cladding material, cast iron is very simple to specify. Cast iron is also 100% recyclable. When no longer needed, items can be turned into new castings.

Cost

Cast Iron Columns by Hargreaves Foundry and David Chipperfield Architects at One Pancras Square August 2013

When properly designed, cast iron compares very favourably with other materials used for cladding and structures. The primary cost is in the production of the pattern. As a result, mass production is key to good value.

For example, the pattern for the columns at One Pancras Square cost around £30,000 to make, but only one pattern was required. Of the 396 columns, 200 were identical and the remainder were cast from variations on the same pattern. This makes the production of columns much more cost effective than stone, for example, where most of the cost is in the workmanship of production itself.

If your project requires the production of multiple same (or similar) items, cast iron can therefore be very cost effective. David Chipperfield Architects worked closely with the foundry to make the most out of our many years of expertise in designing castings.

The Design Process

CAD model of cast iron column surface pattern, by David Chipperfield Architects

If you want to look at cast iron for your building project, the first step is to share your design ideas with the foundry, and talk to us about your needs.

At One Pancras Square, the architects wanted to use Cast Iron for its historical association with the site, but did consider other materials. The choice of cast iron was ultimately made in liaison with the Foundry.

We look at how your designs can be cast, and how the casting process could be made most cost effectively. If we can make a single larger casting rather than two, this can considerably reduce cost. Different grades of material are available depending on whether the design needs to perform structurally.

At One Pancras Square, project architect Mathias Kunz designed a 3D model of the weave surface, and supplied this as a CAD file [Pictured Right - click the image for a larger version]. Our patternmaker then formed a physical model of the surface on a CNC machine, and the patterns were built in resin from that. The architects also supplied a 2D drawing of every column variation, developed in liaison with the Foundry to ensure the most cost effective design.

Find out More

In use in construction for centuries, modern Cast Iron can be a sustainable, cost effective, locally sourced product for structural and aesthetic applications.

To talk about your project, contact Andy Knight, Foundry Manager at

aknight@hargreavesfoundry.co.uk

Tel: 01422 399111

Contact us via Linkedin or Twitter or speak to Andy on Twitter.

More information about the cast iron columns at One Pancras Square can be found in our case study.

 

Here is a time lapse movie of the column casting, shot by John Sturrock: Read about the movie here.