Eden Project

Rammed earth at the Eden Project was the first big project in the UK using rammed earth for 80 years. The Eden Project was built to show the relationship between humans and plants, the good, the bad and the ugly. Of course construction is known to be a big polluter, so environmentally friendly rammed earth was a good choice.

The whole site is a former china clay pit, so access to kaolin was no problem. But in fact the walls were built from a 3m deep fraction of material from above the kaolin, what miners call the overburden. This was a well graded material with clay, sand and stones in the mix.

The material was identified by us and extracted by the main contractor as part of their landscaping works. It was rolled into a 'bund', a pile of soil which was tracked over by a digger to seal the top surface. This sealed the heap against persistent rain, from May to September.

We were asked to take on 60% of the workforce locally and train them. This slowed the mobilisation phase of the job and lead to the whole thing taking 8 weeks instead of the projected 6 weeks. However part of the hold-up was actually that the main contractor hadn't kept far enough ahead with their foundation works!

The 'battered' or leaning face of the outside of the wall initially

caused some issues, the formwork was squeezed upwards until we anchored it down. The formwork was the old 'acrow' type, light weight and with a lot of tricky wedge fittings. The 15mm ply faces gave a slight ripple effect on the face of the walls.

Initially the architects plan to make such enormously thick walls seemed strange, the walls were not high or load bearing. Once we had understood the scale of the project, and the walls were hiding the domes from people coming onto site the walls couldn't be monumental enough.

On such a large site it can be hard to control the working conditions. For instance we worked under an incomplete roof which caused waterfalls onto the new wall at 5m intervals. We were obliged to set up temporary gutters to divert the rain, but these were regularly cut down by other trades. Without the support of the main contractor vigilance is vital!

In all about 270 tonnes of soil were used, placed into the formwork in 150mm deep fills and rammed. The walls have suffered a flash flood as well as the vast passing footfall that the Eden Project enjoys. The flood did little visible damage to the rammed earth, but destroyed the floors internally, the services, the dry-wall, the stock, all in a couple of hours. The rammed earth meanwhile...

The cost of the walls at the time was £70 per metre square, an extremely competitive rate! After the flood they were given a bit of expert care with earth plaster on some worn areas. In particular the 'shadow gap' at the bottom of the wall had not fared well. Rammed earth takes many types of finish, none more so than clay plasters. Once Clayworks realised that clay was the binder in the walls they were happy to go ahead with clay plaster.