The soil is one of the oldest building material used by man. Many buildings that were constructed with soil more than 3000 years are still in existence. The use of earth for building construction was learnt and mastered by doing, and knowledge has passed down to generations. Compressed stabilised earth blocks (CSEB) is the most recent of more than ten construction methods that have documented for soil based construction. Initially, the Europes in the 19th century made first attempts for compressed earth blocks. They used small precast blocks of rammed earth and utilized hand rammers to compress the wet soil into a small wooden mould held with the feet.
In India, the formation of ASTRA (Application of Science and Technology in Rural Areas) in the early seventies represented new initiatives in the use of the stabilized earth. During ASTRA research and development project a lot of Engineers and Architects were trained in Earth Block Construction.
Compressed Stabilized Earth Blocks (CSEB) require moist soil to squeeze under a high amount of pressure to form blocks. The main constituents are of the dry inorganic subsoil, non-expansive clay, aggregates and Portland cement. Many believe that CSEB is the new alternative to clay blocks. The moistened soil used in both stabilised or non-stabilized compressed earth block which is then poured into a steel press and then compressed either with a manual or motorised press. But most of the times, they are stabilised with cement or lime. With cement stabilisation, the blocks must cure for four weeks after manufacturing. After drying, they can use it with a soil cement stabilised mortar.
The versatility of mud block has been :
Low-carbon footprint and high energy efficiency
Being of the earth from the site itself they reduce the ecological footprint to a very high level when combined optimally with natural ventilation, water management (rainwater harvesting), energy management (solar power). Due to their thermal mass quality, CSEBs can save anywhere between 10-15% on cooling and heating costs.
Block strengths can be varied as required making it a safe material that could be used for construction.
Variety in block dimensions leads to the construction of different walls of various sizes which help in passive solar design.
The block which obtained from the soil on site merges into the landscape because of its natural colour and texture. The most significant advantage is there is no need for plastering and painting which saves considerably and is also aesthetically appealing.
Some designers plan to incorporate basement/semi-basements in buildings to not only provider thermally stable space but to generate enough earth for construction of whole house using CSEB. Thus in a 30X40 ft. Site, a basement of size 10x10x5 will be more than enough for generating earth for Ground+1 structure construction.
Despite all the positives, there are certain limitations associated with Compressed Stabilized Earth Blocks such as :
- Mud blocks when left un-plastered absorb light and rooms can tend to be dull.
- Highly skilled labour is required to do pointing with right mortar mix and tools.
- Blocks used for parapet tends to develop a mossy (green) growth.
- Requires quality check at every stage of the construction process.
- Not suitable for high-rise buildings and wide-spans areas.
Not every soil is suitable for earth construction and CSEB in particular. But with some knowledge and experience, many soils can be used for producing CSEB. Topsoil and organic soils, in particular, must not be used. Identifying the properties of soil is essential for a good result
Weathering sometimes plays a significant concern while using earth blocks. Raising the plinth and providing projections wherever necessary, plastering outside or applying silicon coating are some ways to fight the weathering issue.
It is quite evident that CSEB construction requires proper training for understanding the construction and design process. The combination of good aesthetics, low-ecological footprint, low-cost construction are the key points when appropriately marketed will result in extensive use of such techniques.