Selection of the earth to be used for SRE walls is critical to their strength, durability and appearance. Once a sub-soil or crushed material has been found that appears to have suitable physical characteristics and is in a colour acceptable to the client, it should be sent to a soil laboratory for testing. A laboratory can determine the particle sizes by sieve tests, whether it is likely to shrink during drying and most importantly what strength the final compacted material will achieve. The architect or engineer will usually specify the technical properties required according to the building structure, the weather conditions, etc. The mix of particles and stabiliser can be tailored to meet the requirements of the particular job. Sample cores are usually taken during the construction process to confirm that the correct mix and physical qualities are being maintained.

The earth is thoroughly blended with (normally) between 5 and 7% stabiliser, a water-repellent admix and just enough water to form a damp mix. This is placed in pre-set formwork in 150mm to 200mm courses of loose mix. Each course is pneumatically rammed to maximum compaction, then the next course is laid on top and the process repeated. Forms are set, filled and reset in vertical progression to the top of the wall. Each column or wall section is completed and left to harden, normally just overnight, before stripping the formwork to reset for the next section.

The formwork system used by asEg member firms has been developed over 25 years specifically for this earth building process and is patented. It has to be able to withstand the high pressures developed during the ramming process, remaining rigid without distorting from the correct alignment and yet be quickly and simply erected with little mechanical handling. An understanding of this process is important if the building designer is to make use of the inherent efficiencies of the formwork system and minimise the labour cost.