COMPRESSED STABILISED EARTH BLOCKS
A MODERN TECHNOLOGY
The soil, raw or stabilized, for a compressed earth block (CEB) is slightly moistened, poured into a steel press (with or
without stabiliser) and then compressed either with a manual or motorized press. CEB can be compressed in many
different shapes and sizes. For example, the Auram press 3000 proposes 16 types of blocks.
The input of soil stabilization allowed people to build higher with thinner walls,
which have a much better compressive strength and water resistance. With
cement stabilization, the blocks must be cured for four weeks after
manufacturing. After this, they can dry freely and be used like common bricks
with a soil cement stabilized mortar. Since the early days, compressed earth
blocks are most of the time stabilised.
Auram hollow interlocking block 295
Therefore, we prefer today to call them Compressed Stabilised Earth Blocks
SOIL SUITABILITY AND STABILIZATION FOR CSEB
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 must not be used. Identifying the properties of a soil is essential to perform, at the end, good
quality products. Some simple sensitive analysis can be performed after a short training.
A soil is an earth concrete and a good soil for CSEB is more sandy than clayey. It has these proportions:
According to the percentage of these 4 components, a soil with more gravel wil be called gravely, another one with
more, sand, sandy, others silty or clayey, etc. The aim of the field tests is to identify in which of these four categories the
soil is. From the simple classification it will be easy to know what to do with this soil.
A very few laboratories can identify soils for building purposes. But soil identification can be performed by anybody with
sensitive analyses. The main points to examine are:
Grain size distribution, to know quantity of each grain size
Plasticity characteristics, to know the quality and properties of the binders (clays and silts)
Compressibility, to know the optimum moisture content, which will require the minimum of compaction energy for the
Cohesion, to know how the binders bind the inert grains
Humus content, to know if they are organic materials which might disturb the mix
Many stabilizers can be used. Cement and lime are the most common ones. Others, like chemicals, resins or natural
products can be used as well.
The selection of a stabilizer will depend upon the soil quality and the project requirements:
Cement will be preferable for sandy soils and to achieve quickly a higher strength.
Lime will be rather used for very clayey soil, but will take a longer time to harden and to give strong blocks.
The average stabilizer proportion is rather low:
No technical maximum
These low percentages are part of the cost effectiveness of CSEB.
BASIC DATA ON CSEB
Dry compressive strength at 28days
4 to 6 Mpa = 40 to 60 Kg/cm2
(+10% after 1 year + 20% after 2 years)
Wet compressive strength at 28 days
2 to 3 Mpa = 20 to 30 Kg /cm2
(after 3 days immersion)
Dry bending strength (at 28 days)
0.5 to 1 Mpa = 5 to 10 Kg /cm2
Dry shear strength (at 28 days)
0.4 to 0.6 Mpa = 4 to 6 Kg /cm2
Water absorption at 28 days (after 3 days immersion)
8 to 12% (by weight)
Apparent bulk density
1700 to 2000 Kg/m3
Energy consumption (Ref. Development Alternatives 1998)
(To be compared with kiln fired bricks (wire cut) = 539 MJ and country fired bricks = 1657 MJ
TYPICAL BLOCKYARD ORGANISATION
Costs are too often limited only to a monetary value. Another important aspect is the energy consumption involved in the
material. The production of earth-based materials consumes much less energy and pol utes much less than fired bricks.
CSEB and stabilised rammed earth are much more eco-friendly.
They have these advantages compared to fired bricks:
Pollution emission (Kg of CO2 /m2) Energy
2.4 times less than wire cut bricks
4.9 times less than wire cut bricks
7.9 times less than country fired bricks
15.1 times less than country fired bricks
Ecological comparison of building materials
Product and thickness
No of units Energy consumption CO2emission
Dry compressive crushing
(MJ per m²)
(Kg per m²)
CSEB – 24 cm
40 – 60
Wire Cut Bricks – 22 cm
75 – 100
Country Fired bricks – 22 cm
30 – 50
Concrete blocks – 20 cm
75 – 100
Note: Wire Cut bricks are also called Kiln fired bricks. (Source: Development Alternatives – 1998)
CSEB are most the time cheaper than fired bricks. This will vary from place to place and specially according to the
cement cost. The cost break up of a 5 % stabilised block would depend on the local context. It would be within these
figures, for manual equipment with an AURAM press 3000:
Labour: 20 - 25 %
Soil & sand: 20 - 25%
Cement: 40 - 60 %
Equipment: 3 - 5 %
The strength of a block is related to the level of compression and to the quantity of stabiliser. This implies that to reduce
the cost of a block one should try to reduce the quantity of cement but not the cost of the labour with unskil ed people.
One should also not cut down the cost of the press with cheap quality machines, which would not last and would not give
In the context of Aurovil e, a finished m3 of CSEB masonry is always cheaper than fired bricks: 19.4% less than country
fired bricks and 47.2 % less than wire cut bricks (March 2004). See comparison of building materials in Auroville.
ADVANTAGES OF CSEB
A local material
An adapted material
Ideally, the production is made on the site itself or in the
Being produced locally it is easily adapted to the various
nearby area. Thus, it will save the transportation, fuel,
needs: technical, social, cultural habits.
time and money.
A transferable technology
A bio-degradable material
It is a simple technology requiring semi skills, easy to
Well-designed CSEB houses can withstand, with a
get. Simple vil agers will be able to learn how to do it in
minimum of maintenance, heavy rains, snowfall or frost
few weeks. Efficient training centre will transfer the
without being damaged. The strength and durability has
technology in a week time.
been proven since half a century.
But let’s imagine a building fallen down and that a jungle
A job creation opportunity
grows on it: the bio-chemicals contained in the humus of
CSEB allow unskilled and unemployed people to learn a
the topsoil will destroy the soil cement mix in 10 or 20
skill, get a job and rise in the social values.
years… And CSEB will come back to our Mother Earth!
According to the local context (materials, labour,
Firewood is not needed to produce CSEB. It will save the
equipment, etc.) the final price will vary, but in most of
forests, which are being depleted quickly in the world,
the cases it will be cheaper than fired bricks.
due to short view developments and the mismanagement
Produced locally by semi skilled people, no need import
Management of resources
from far away expensive materials or transport over long
Each quarry should be planned for various utilisations:
distances heavy and costly building materials.
water harvesting pond, wastewater treatment, reservoirs,
landscaping, etc. It is crucial to be aware of this point:
Flexible production scale
very profitable if well managed … disastrous if
Equipment for CSEB is available from manual to
motorized tools ranging from village to semi industry
scale. The selection of the equipment is crucial, but once
Energy efficiency and eco friendliness
done properly, it will be easy to use the most adapted
Requiring only a little stabilizer the energy consumption in
equipment for each case.
a m3 can be from 5 to 15 times less than a m³ of fired
bricks. The pollution emission will also be 2.4 to 7.8 times
less than fired bricks.
Demonstrated, since long, CSEB can adapt itself to
various needs: from poor income to well off people or
governments. Its quality, regularity and style allow a
Produced local y, with a natural resource and semi skil ed
wide range of final house products.
labour, almost without transport, it will be definitely cost
effective! More or less according to each context and to
To facilitate this acceptation, banish from your language
“stabilized mud blocks”, for speaking of CSEB as the
latter reports R & D done for half a century when mud
blocks referred, in the mind of most people, as poor
SOME LIMITATIONS OF CSEB
Proper soil identification is required or lack of soil.
Over-stabilization through fear or ignorance, implying
Unawareness of the need to manage resources.
Ignorance of the basics for production & use.
Under-stabilization resulting in low quality products.
Wide spans, high & long building are difficult to do.
Bad quality or un-adapted production equipment.
Low technical performances compared to concrete.
Low social acceptance due to counter examples
Untrained teams producing bad quality products.
(By unskilled people, or bad soil & equipment).
DIVERSITY AND SELECTION OF THE PRODUCTS
The development of CSEB proposes nowadays a wide range of products, from different size and shapes. To select the
most adapted product to one’s need, one should pay specially attention to these factors:
Module of the block
It is the block size plus the mortar thickness. Choose preferably an easy module, in the
decimal system, to avoid wasting time for the design calculations. Select also the
module with the thinnest mortar joint possible.
Possibilities of different According to the module of a block, which thickness of wall can be achieved with easy
bonds? According to the thickness, one can know if a block can be load bearing or not.
Area of the block
The bigger it is, the weaker the block will be. A large area will require great compaction
energy: a manual press with 15 T. capacity will not be able to compress properly more
than 600 cm².
Plain, hollow or
Each of them has different possibilities: plain ones will be laid with a thick mortar (1 to
1.5 cm); hollow ones will be laid with a thin mortar (0.5 to 1 cm); the interlocking blocks
will require a thin mortar (0.5 cm) and very special details.
Whether a mould can do full size, 3/4 of half block. To do proper bonds, one needs to
use these 3 sizes in order to achieve a good quality, without breakage.
DIVERSITY AND SELECTION OF THE EQUIPMENT
Many attempts were tried to use concrete equipment to produce CSEB. All failed, as the requirements of the materials
and the working conditions are different. Today, available on the market are a wide range of specialized equipment
adapted to each need and scale of production. Today one can find manual presses, light or heavy, motorised ones
where the compression energy is given by an engine. One can also find mobile units, which also integrates a crusher
and a mixer in the same machine.
A cheap manual press, thus light and attractive in price, will not be so long lasting. A motorized press will present the
advantage of a high productivity, with a better and more regular quality. But it will require energy and a more complicated
maintenance, and its cost wil have no comparison with a manual press. Besides a press, one should not forget all the
other equipment required: sieve, maybe a crusher, wheelbarrows, maybe a mixer, quality control devices, all small tools,
PVC sheets, etc.
Therefore, it appears that in the Indian context, manual and heavy presses are better adapted than motorised ones, as
they would employ more people and would produce quality materials at cheaper rates.
OPTIMIZATION OF INVESTMENT / OUTPUT / QUALITY RATIO
Light manual equipment presents the advantage of being cheap, but the disadvantage of a low durability, a low output
and not very well compressed blocks. Heavy manual equipment presents a more interesting ratio, with more output,
more durability and more strength for a subsequent increase of costs.
Motorized equipment steps into another category of cost: it will produce better quality blocks with more output, but more
expensive. Therefore, heavy manual presses are most of the time the best choice in terms of optimisation for the
investment/output/quality ratio. Mobile-units are always coming far behind.
Industrialization is not adapted to the production of CSEB. Semi industrialization is the best: it offers the advantage to be
more flexible and easily adapted to a local context. It increases the quality without increasing tremendously the cost of a
block. Semi industrialization should be understood here as a centralized production, but rather with manual presses than