SRE builders worldwide use cement as a stabiliser in their rammed earth walls because it makes them strong, durable and maintenance free. By selecting particle sizes that will lock together and using pneumatic tampers to compact them, it is necessary to use only a small percentage of cement to bind the earth into a solid, strong and water-resistant material.

But cement production requires lots of energy and produces CO2. These are environmental liabilities which, when considered on their own and in the short-term cause the use of cement to be regarded unfavourably. Other stabilisers have been tried; bitumen, lime, acrylic, etc., but cement makes the best walls that last the longest. They require no extended eaves, no regular coats of lime wash and they don’t fall down when they get wet. Consequently, when considered in the longer term, i.e. the life of the building, cement stabilised earth walls are far better, safer and require less energy than unstabilised earth walls or walls built using other stabilisers.

Some environmentalists suggest that the most sustainable building method is to return to the old ways of building in “Natural” or Unstabilised Rammed Earth. But these walls remain soluble, are eroded by rain and will collapse when soaked. Thus they need protecting with wider eaves, which means that the whole roof has to be larger. Unstabilised walls are not as strong and thus must be thicker, usually twice as thick. This means larger concrete foundations. If they are loadbearing, as most walls are, they need a concrete ringbeam cast on top of the wall. To protect them from wind driven rain they need either weatherproof cladding or a coating of lime render or lime wash. The lime coatings deteriorate and need to be regularly replaced. Hydraulic lime is a fired product with environmental liabilities similar to cement so regular treatments of this will soon equate to a small amount of cement used within the wall.

When the effects of all these factors upon the overall design of the building and its long-term maintenance requirements are considered, it is clearly seen that Unstabilised Earth Walls are far less sustainable than they may initially appear.

Brick is a long lasting material that requires little or no maintenance, which explains its long-term popularity and predominance. However, because of the large amount of energy requirement for firing, the transport usually required from a centralised production plant and then the cement that must be used in the mortar to lay the bricks, brick walls have a very high initial embodied energy. When considered in the long-term brick has a relatively poor embodied energy rating.

Concrete blocks are becoming very common in modern building practice. Whilst they do not need to be fired, they do contain a high proportion of cement and usually need transporting a considerable distance from the production plant. Most importantly however, they do not provide a finish that is suitable for either interior or exterior surfaces. Thus the additional materials and processes required to make these finishes must be included when assessing a block wall. Calculations of the embodied energy of these walls vary as do their components. However they are well above that of SRE walls in almost all cases.

For the reasons explained above it can be shown that Stabilised Rammed Earth walls have a lower embodied energy than finished brick or block walls. They also have a lower embodied energy than Unstabilised Earth Walls when the additional energy requirements of necessary changes to the building design and long-term maintenance requirements are taken into account.