Most of us wish to have a perfect home to live in for decades. But for one to have this dream home, one needs a reliable and professional builder who will help him to access quality materials at a lower and affordable cost. The builder has to ensure that the structure, materials and quality of the work are at their best in order to get a house that lasts for years.
There has been a renewed interest in the use of stabilised earth blocks due to its low cost and eco-friendly properties. These types of blocks are a mixture of soil, sand, a stabiliser (often cement) and water.
Seth Eyeru, a builder with Eco-Construct Uganda Limited says earth blocks are also known as compressed stabilised earth block (CSEB), stabilised soil blocks (SSB), stabilised earth blocks (SEB) and are produced from stabilised soil which is slightly moistened, poured into a press and then compressed either with a manual or motorised press.
The quality of brick which can be made at a particular site is largely predetermined by the type of soil available.
“The soil can be stabilised with either cement or lime but cement has been found to be easier to use as a stabiliser. The blocks must then be cured for about fourteen days or longer before use. The type of soil to be used to make stabilised soil blocks has to be chosen carefully as top soil and organic/loam soils cannot be used if one would like to end up with a good quality product,” Eyeru says.
CSEB can be compressed into many different shapes and sizes and one common shape is the interlocking stabilised soil block (ISSB) which has been used in many construction projects in the region. “These blocks have been used by many private contractors, Non-Governmental Organizations (NGOs) including the likes of the Good Earth Trust, UN-Habitat, CARITAS, Connect Africa and Hailey-bury Youth Trust among others,” he adds.
Types of CSEB bricks in the market
The compressed stabilised earth blocks in the market are of many types and these depend on the press that has been used to mould the blocks.
“There are many presses in the market from the manual ones manufactured in the East African region to the imported mechanised ones like Hydraform M7 E380 machine. These presses make many types of bricks like the standard soil block, interlocking soil blocks, hollow blocks through which steel reinforcement can be placed within the block, and even special blocks through which act as formwork for ring and plinth beams,” explains Ereku.
Many people get confused while choosing between these bricks. However each has their own unique features so you need not conclude that a building made of cement bricks is less strong provided that the foundation is good.
“CSEB production results into high quality block, uniform in size and shape with defined edges and smooth surfaces that makes construction easier and one to come up with an attractive site. CSEBs use less mortar and produce less waste as the soil can be reused to produce more blocks. These blocks don’t necessarily have to be plastered hence the cost of building materials especially cement is significantly lower, the amount of mortar also used between the blocks is also minimal as the blocks can also be interlocking,” he says.
Unlike other bricks including the common burnt clay bricks, sand lime bricks, fly ash bricks, concrete bricks, and fire clay bricks, CSEBs are cured on site and not fired using firewood.
Advantages and disadvantages of compressed stabilised earth block (CSEB)
Since soil is available in large quantities in most parts of the country, making CSEB is less expensive because less transportation is required for raw materials. Excavated soil can be considered as a raw material instead of waste as is the case on most building sites.
“It is also cheap and affordable because in most parts of the world soil is easily accessible to low-income groups thus reduces the expensive cost incurred in building compared to other types of blocks. Besides they provide decent shelter to many. Also the curing process doesn’t need burning with firewood thus it reduces the environmental damage for example in quarrying for clay,” explains Julius Jojo, an architect.
This type of brick also has beneficial climatic impact due to its high thermal capacity, low thermal conductivity which can moderate extreme outdoor temperatures and maintain a satisfactory internal temperature balance in comparison to concreted blocks.
Unlike the production of fired bricks, firewood is not required to produce CSEBs which prevents the depletion of forests.
“The use of natural, locally available materials makes good housing available to more people, and keeps money in the local economy rather than spending it on imported materials, fuel and replacement parts. Besides uniformly, sized building components can result in less waste, faster construction and the possibility of using other pre-made components or modular manufactured building elements.
Disadvantages of CSEB
CSEB do have some limitations in relation to fired blocks and the major limitation is unsuitability of soil in the production of blocks.
“Bad quality or inappropriate equipment in the production of blocks can also lead to a poor quality block. Many builders are also not aware of the basic principles of CSEB use for example they need to be protected from rain by providing a good over-hang of minimum 600mm,” he says.
CSEB materials need to be chosen carefully as over-stabilisation arises due to fear or ignorance resulting in high costs and under-stabilisation resulting in very low quality products. “It should be noted that compressive strength of compressed stabilized earth building blocks (that is, the amount of pressure can resist without collapsing) depends upon the soil type, amount of stabilizer and the compaction pressure used to form the block. The minimum should be 2.5 MN/m2 and stronger blocks would be obtained by proper mixing of suitable materials and proper compacting and curing. A delicate balance needs to be struck for a good quality block to be produced,” Jojo states.