We have used unfired earth blocks in WISE because they have a low embodied energy, will be easily re-cycled on demolition, add thermal mass to the ground floor, give good sound insulation between teaching spaces and are easy to use for conventional workers.
We used 'Sumatec' rammed earth blocks, which were originally made by Limetec and supplied to us by Ibstock, but are nowadays supplied by a company called Backtoearth. The blocks cost us £40.83 per square metre.
Some difficulties were faced due to the use of a non-durable material by a conventional contractor – the blocks were not sufficiently protected from the weather. Otherwise the products were very workable – we could have used a clay slurry to bed the blocks, but the contractor preferred an hydraulic lime/sand mortar. Once rendered with a lime render, the blocks were strong and stable. There have been no shrinkage cracks.
We have previously used rammed earth blocks for a cavity wall with no problems, and we would do it again. In future we would try using the blocks as a 100mm partition (we laid them flat – 178mm thick). Also we have only used them in a non-loadbearing situation, but they could easily support normal building loads.
In another building at CAT, the large 'shed' for our biomass CHP (combined heat and power) system, we used 'Ecoterre' unfired clay blocks, finished with lime render. These are softer and so not as strong, and were supplied by Ibstock. The bricks are dried using waste heat from a brick kiln – using a lot less energy than conventional cement blocks. The high density of these blocks make them ideal for sound attenuation, a very important consideration in this building as the turbine is quite loud – we designed the building so that it will be inaudible outside. The CHP building covers 260 square metres and is 7 metres high.