At 7.2 metres, the circular lecture theatre walls will be the highest rammed earth walls in the UK, and will be an impressive feature of the new building.

Rammed earth, or pise de terre, consists of loose, moist subsoil compacted in thin layers between shuttering or formwork. Mechanical compaction forces clay molecules to bond with the aggregate – this is a physical rather than chemical bond – giving the wall it’s strength. Particle size and grading, moisture content, and clay content are all critical to the performance of the finished wall.

Llynclys Quarry near Oswestry was identified as source of suitable material (the earth for the walls in the Atteic building also came from Llynclys), and samples of several different materials were taken for testing. The material chosen was a waste product that had already been processed, and had a suitable grading of 6mm particles downwards. The material has been delivered to CAT in tonne bags ready for use.

The earth will be rammed into a proprietary circular shuttering system which has an adjustable radius. The material will be put into the shuttering in 150mm layers, and compacted using a hand held pneumatic ram. The circular walls will be formed in four sections, with 2 full height gaps for doors. The rammed earth provides structural support for the roof, but does not form the external walls, which are of glazing on the south side, and hemp and lime along with the rest of the building; there is a corridor around the theatre between the rammed earth and the external walls.

WISE is the first building that Frank Galliers have worked on that uses rammed earth, so earth specialists Rowland Keable of Ram Cast CIC (www.rammed-earth.info) and Andy Simmonds (www.simmondsmills.com ) have been brought in to aid in the design and build process. All work will be done by Galliers, and a recent test panel proved very successful.