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Introduction of
structural clay and its
classification&
Properties
By: Ar Amandeep Kaur
Ar. Naina Malhotra
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Building Materials: Clay
• In nearly all hot-arid and temperate climates, earth has always been the most prevalent
building material. Even today, one third of the human population resides in earthen
houses; in developing countries this figure is more than one half.
• Mud and fieldstone are the earliest walling materials met within buildings that remain in
use today. Both have continued in use throughout recorded time into the beginning of this
century.
• A limited amount of rubble stonework is still built today and there are a few people living
who can give first-hand accounts of buildings with mud.
•Construction in these materials is necessarily massive and openings are small, givingbuildings of these types very high qualities of thermal insulation.
• Mud is found in use in three forms: monolithic; in courses bonded with straw; and as
unbaked bricks. The material is strong and perfectly stable as long as it is kept reasonably
dry and for this reason it was always lime washed.
• The walls however require some moisture to keep their binding and can fail if too dry.
Insertion of damp proof courses are not recommended for mud walls for this reason. Anumber of vernacular buildings across Northern Ireland have mud walls. Sometimes these
may have been patched or built up by stone or brick and can be hard to recognise before
work starts.
• Mud was also used as a binder in rubble stone construction, when it was often mixed with
lime.
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Mud Construction
• Mud as a construction material has beenextensively used since Neolithic times.
• Mud construction is mainly found in places
which are – rural
– relatively dry and
– have mud in abundance.
• SOIL SOURCE
– Mud required for building can be taken
from the plot itself. – The soil is collected after depth of
60cms only.
– As the top layer is full of organic matter,it isn’t used.
– Below it is sand and clay which are dugout in heaps.
– Do not use hard rock.
– Soil to be used should be devoid of organic matter.
– Top should be replaced after excavating.
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SOIL TYPE
• Gravel: Small pieces of stone varying from the size of a pea to that of an egg.
• Sand: Similar small pieces of stone (usually quartz), which are small but each grain, is visible
to the eye.
• Silt: The same as sand except that it is so fine that you cannot see individual grains.
• Clay: Soils that stick when wet - but very hard when completely dry.
• Organic Soil: Soil mainly composed of rotting, decomposing organic matters such as leaves,
plants and vegetable matter. It is spongy when wet, usually smells of decaying matter, is dark
in color and usually damp.
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SOIL USABILITY
• Gravel: alone is of no use for mud wall building - the tiny lumps of stone
have nothing to bind them together.
• Sand: similar to gravel, it is of no use for wall making by itself - but if
mixed with clay, it is the ideal mud wall building soil.
• Silt: by itself is also no good for building walls. It will hold together but is
not strong. Furthermore, it will not compact so it is also of no use for
pressed blocks or rammed earthwork.
• Clay: can be rammed or compressed but in drying out they often shrink.
During the monsoon they get damp and expand again and crack form.
• Organic Soils: are mainly useless for wall building.
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Soil Tests
•There are two kinds of tests: – Field tests
• Color tests
• Touch and smell test
• Biscuit test
• Hand wash test
• Cigar test
• Adhesion test
– Lab tests
• Sieve test
• Sedimentation test
Earth, when used as a building material, is often given different names. Referred to in
scientific terms as loam, it is a mixture of clay, silt (very fine sand), sand, and occasionally larger
aggregates such as gravel or stones.
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• COLOUR TEST
• Procedure
– Observe the color of soil.
Interpretation
Deep yellow, orange and red, ranging to deep browns indicate iron contentwhich is good as building mud.
Greyish or dull brown, ranging to dirty white indicates more clay.
Dull brown with slightly greenish colour indicates organic soil.
• TOUCH & SMELL
• Procedure
– Rub small quantity of dry soil on palm to feel its texture.
– Moisten the soil and rub again.
– Pure loam is odourless, however it acquires a musty smell if it contains
deteriorating humus or organic matter.
Interpretation Soil that feels coarse when dry but sticky when wet contains lumps of clay.
Soil that feels coarse when dry but gritty when wet contains sand.
Soil that feels coarse when dry but little gritty when wet contains silt.
If the wet soil gives off musty smell then it contains organic matter .
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• BISCUIT TEST
• Procedure
– Make a smooth paste from the soil removing all gravels.
– Mould it into a biscuit of 3cm diameter and 1cm height.
– Leave it to dry and observer for shrinkages or cracks.
– Break the biscuit to noting how hard it is.
Interpretation
If biscuit cracks or leaves gap from the mould then it contains more clay.
If its very hard to break then soil contains more clay.
If itbreaks easily
and can be crumpled between finger then it hasgood sand-clay proportion.
If breaks and reduce to powder then the soil has more sand or silt.
• HAND WASH TEST
• Procedure
– Play with wet soil till your hands get thoroughly dirty. – Wash your hands to see how difficult it is to clean.
Interpretation
If hands get cleaned quickly, then soil contains more sand.
If it takes little time to clean and feels like flour then soil contains more silt.
If it feels soapy or slippery and takes time to clean then soil contains more clay.
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• CIGAR TEST
• Procedure
– Make a smooth paste from the soil removing all gravels.
– Roll it on palm to make a cigar.
– Slowly push it outside your palm.
– Measure the length at which it breaks.
Interpretation
Length below 5cm - too much sand.
Length above 15cm - too much clay.
Length between 5cm to 15cm - good mixture of sand and clay.
• ADHESION TEST
• Procedure
– Make a ball out of wet soil.
– Pierce a knife into it and remove.
– Observe the knife after removing.
Interpretation
If little soil sticks on the knife then it has more silt.
If lot of soil sticks on the knife then it has more clay.
If the knife is clean after removal than the soil has more sand.
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• SIEVE TEST
• Procedure
– Pass soil from series of standard sieves set on
top of on another with finest sieve at bottom.
– Observe the soil collected in each sieve.
Interpretation
Silt will be collected in lowermost sieve.
Gravels will be collected on top.
Sand and lumps of clay will be collected in
intermediate sieves
• Sedimentation test
– Procedure
– Take a transparent cylindrical bottle or jar of 1Lt.
Capacity.
– Fill it with ¼ soil and ¾ water.
– Shake well and allow it to settle for 30 min.
Interpretation
Coarse gravels will be settled at bottom,
followed by sand, silt and clay on top.
Measuring the layers will give us the
approximate proportions of each content.
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• Cob• Pise or Rammed earth
• Adobe
• Pressed bricks
• Wattle and daub
method
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SYSTEMS OF BUILDING
• COB is good for anything except height. It is particularly good for curved or round walls.
• PISE OR RAMMED EARTH is strong and ideal for solid, squat, single storey houses.
• ADOBE or SUN DRIED BRICKS can easily cope with two storey houses.
• PRESSED BRICKS smooth and very strong and can build three storey.
• WATTLE & DAUB is elegant and fine for Seismic Zones.
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COB
• With only a little water to form a very stiff mud, a large lump is roughly moulded into the shape of
a huge elongated egg.
• The usual size is anything between 12 to 18-inches, (30 to 40-cm) long and about 6-inches (15-cm)
in diameter.• A row of these cobs of mud are laid neatly side-by-side - preferably somewhat pressed together.
• Then another row of cobs is laid on top.
• When three or four courses have been laid, one above the other, the sides are smoothed over so
that the holes and cracks disappear.
• Openings for doors, and windows are a problem, which can be solved by using temporary vertical
planks or shuttering.• Another very simple shuttering for openings is to use empty kerosene tins.
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COB
RAMMED EARTH
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RAMMED EARTH
• The second method has developed from the cob wall so as to standardize or regularize the thickness of
the wall.
• It is also an attempt to increase the strength of the wall by ramming it. It is known as the Rammed Earth
method.
• Two parallel planks are held firmly apart by metal rods and clips or bolts, or by small crosspieces of wood.
• Stiff mud is thrown in between these two planks and rammed down with either a wooden or metal
ramrod.
• When one section is completed and hard, the two boards are moved along and the process is repeated
• The two planks are then raised up and a second course of rammed earth is repeated over
ADOBE
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ADOBE
• Blocks shall be kept covered with air tight polythene sheets for first 48 hrs with relative humidity
up to 100.
• Polythene sheets shall be removed after 48 hrs and the blocks shall be kept in shaded area like
having enough air circulation.
• Sprinkle water over blocks daily, as many times needed, during 28 days.
• Write date of production on block corner.
• Cover stacks top with coconut leaves or any other cover to avoid direct sunlight.
• Principle is that blocks shall not dry for 4weeks.
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PROPERTIES OF MUD BRICKS
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PROPERTIES OF MUD BRICKS
Longevity: Mud bricks are the world's oldest manufactured building material and they have stood the test of
time. As testimony of mud bricks strength and durability, the Great Wall of China (210 BC) was built of both
burned and sun-dried mud bricks. Proof that your mud brick home will not only be enjoyed by you but by
generations to come.
Energy Efficient: Mud brick homes are very energy efficient being warm in winter and cool in summer. The
thick, solid walls of a mud brick home act as a buffer to extremes of weather during both winter and summer.
Aesthetics and Acoustics: A mud brick home looks great! It blends with the environment and has a warm
welcoming feel. The mud brick walls absorb sound and reduce echo, producing a home that is quiet and serene.
Easy to Lay: Whether a professional brick layer or a novice, mud bricks are easy to lay. The bricks are the same
material as the mortar and as a result they don't need to be laid perfectly. In fact the variations in a mud brick
wall give it character.
Environmentally Sound: Our mud bricks are an environmentally sound choice being made from natural
materials and requiring very little energy to produce. They are sun dried and simply manufactured and
therefore have a very low embodied energy.
Fire Resistance: The recent Victorian Bushfires have highlighted the excellent fire rating of mud bricks. Typically
earth walls are thick and slow to heat up. A standard 250mm thick mud brick wall has a 4 hour fire rating
meaning that it takes 4 hours for the heat in an intense fire to transfer through the brick. The Australian
requirement for buildings in fire prone areas is generally a 1.5 hour fire rating. This makes mud bricks highly
suitable for building in bushfire prone areas and for the construction of fire rated walls within buildings.
Economical: There are considerable cost savings in building a mud brick home as they are generally built as a
single-skin structure and are also load bearing. This eliminates the need for a timber framework, insulation,
gyprock and paint, saving your money.
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Structural Considerations
• Soil Composition
• In general mud bricks can be made with most soils having clay contents between 5% and
45% and with at least 30% sand and not more than 50% silt
• These bricks are typically
stabilised with bitumen
emulsion (5-12% by
mass) to prevent
excessive water absorption.
• The figure shows the
general range of soil
types used but in the end
an acceptable soil is one
that produces brickswhich are suitable for
their exposure
environment.
PERFORMANCE OF BUILDINGS DURING EARTHQUAKE
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PERFORMANCE OF BUILDINGS DURING EARTHQUAKE
• Different types of buildings suffer different degrees of damage during earthquakes and the
same has been studied here.
1. MUD AND ADOBE HOUSES:
• Mud houses are the traditional construction, for poor and most suitable in view of their
initial cost, easy availability, low level skill for construction and excellent insulation againstheat and cold.
• There are numerous examples of complete collapse of such buildings in 1906 Assam, 1948
Ashkhabad, 1960 Agadir, 1966 Tashkent, 1967 Koyna, 1975 Kinnaur, 1979 Indo-Nepal, 1980
Jammu and Kashmir and 1982 Dhamar earthquakes.
• It is very weak in shear, tension and compression.
• Separation of walls at corner and junctions takes place easily under ground shaking. The
cracks pass through the poor joints. After the walls fail either due to bending or shearing in
combination with the compressive loads, the whole house crashes down.
• Better performance is obtained by mixing the mud with clay to provide the cohesive
strength. The mixing of straw improves the tensile strength.
•Coating the outer wall with waterproof substance such as bitumen improves againstweathering.
• The strength of mud walls can be improved significantly by spilt bamboo or timber
reinforcement.
• Timber frame or horizontal timber runners at lintel level with vertical members at corners
further improves its resistance to lateral forces which has been observed during the
earthquakes.
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WATTLE AND DAUB
• Wattle and daub method is an old and common method of building mud structures.
• There bamboo and cane frame structure that supports the roof.
• Mud is plastered over this mesh of bamboo cane and straws
• Due to excessive rainfall the Wattle and Daub structures gets washed off.
• However, the mesh of cane or split bamboo remains intact and after the heavy rain is over
the mud is plastered on again.
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STABILIZERS
• When the available soil is not suitable enough for construction then the soil can be used by
manipulating its composition by adding suitable stabilizers.
– Stabilizing enhances the given property of the soil type.
– Increase Tensile and Shear strength.
– Reduce shrinkage.
• Most common and effective stabilizer is Soil itself.
• Cement, is the best example of a modern contemporary stabilizer.
• Various other indigenous stabilizers include
–Straw
– Plant Juices
– Gum Arabic
– Sugar Or Molasses
– Cow Dung
– Animal Urine
– Tannic Acid
– Oil
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Stabilised Soil
• Stabilization is necessary to achieve a lasting structure from local soil. The local
material properties determine the appropriate stabilization method. The compressive
strength of the soil can be improved multifold by using the right stabilization method.
The main categories of binders used for earth construction are Portland cement, lime,bitumen, natural fibres and chemical solutions such as silicates.
• Stabilization techniques can be broken down into three categories
Mechanical stabilization:
• compacting the soil and changing its density, compressibility, permeability and
porosity.Physical stabilization:
• changing the texture properties of the soil.
• It can be done by controlling the mixture of different grain fractions, drying or
freezing, heat treatment and electrical treatment.
Chemical stabilization:
• changing the properties of the soil by adding other chemicals or additives.
• This happens either by creating a matrix, which binds or coats the grains or by a
physico-chemical reaction between the grains and the additive materials.
• Many additive materials can be used to stabilize the soil.
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Earth Blocks: Compressed & Stabilised
• The compressed earth block is the modern descendent of the moulded earth block.
• Compressed Earth Blocks, or CEBs, are construction blocks made with clay, sand, and
a stabilizing ingredient such as lime or Portland cement. The earth mixture is poured
into a hydraulic press machine. Since they are machine-made, compressed earthblocks are uniform in size and shape.
• Compressed earth blocks can be stabilised or not.
• Most of the times, they are stabilised with cement or lime. Therefore, they are called
Compressed Stabilised Earth Blocks (CSEB).
•The input of soil stabilization allowed people to build higher with thinner walls, whichhave 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.
• The soil, raw or stabilized, for a compressed earth block 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.
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Compressed stabilised earth blocks by
the Auram press 3000
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ADVANTAGES OF CSEB
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ADVANTAGES OF CSEB
• A local material
Ideally, the production is made on the site itself or in the nearby area. Thus, it will save the transportation, fuel,
time and money.
• A bio-degradable material
Well-designed CSEB houses can withstand, with a minimum of maintenance, heavy rains, snowfall or frost
without being damaged. The strength and durability has been proven since half a century.
But let’s imagine a building fallen down and that a jungle grows on it: the bio-chemicals contained in the humus
of the topsoil will destroy the soil cement mix in 10 or 20 years… And CSEB will come back to our Mother Earth!
• Limiting deforestation
Firewood is not needed to produce CSEB. It will save the forests, which are being depleted quickly in the world,
due to short view developments and the mismanagement of resources.
• Management of resources
Each quarry should be planned for various utilisations: water harvesting pond, wastewater treatment, reservoirs,
landscaping, etc. It is crucial to be aware of this point: very profitable if well managed, but disastrous if
unplanned!
• Energy efficiency and eco friendliness
Requiring only a little stabilizer the energy consumption in 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.
• Cost efficiency
Produced locally, with a natural resource and semi skilled labour, almost without transport, it will be definitely
cost effective! More or less according to each context and to ones knowledge!
A d d i l
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• An adapted material
Being produced locally it is easily adapted to the various needs: technical, social, cultural habits.
• A transferable technology
It is a simple technology requiring semi skills, easy to get. Simple villagers will be able to learn how to do it in
few weeks. Efficient training centre will transfer the technology in a week time.
• A job creation opportunity
CSEB allow unskilled and unemployed people to learn a skill, get a job and rise in the social values
• Market opportunity
According to the local context (materials, labour, equipment, etc.) the final price will vary, but in most of the
cases it will be cheaper than fired bricks.
• Reducing imports
Produced locally by semi skilled people, no need import from far away expensive materials or transport over
long distances heavy and costly building materials.
• Flexible production scale
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 done properly, it will be easy to use the most adaptedequipment for each case.
• Social acceptance
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 wide range of final house products. 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 building material.
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• Proper soil identificationis required or unavailability
of soil.
• Unawareness of the
need to manage resources.
• Ignorance of the basics
for production & use.• Wide spans, high & long
building are difficult to do.
• Low technicalperformances compared to
concrete.
• Untrained teams
producing bad quality
products.
• Over-stabilizationthrough fear or ignorance,
implying outrageous
• Under-stabilizationresulting in low quality
products.
• Bad quality or un-
adapted production
equipment.
• Low social acceptancedue to counter examples
(By unskilled people, or bad
soil & equipment).
SOME LIMITATIONS OF CSEB
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Mud Building Technology
• Mud is easily eroded by water which makes it difficult to use in areas with heavy rainfall.
• It is also susceptible to mechanical damage, making it easy for rodents to dig holes into mud
walls.
• Mud houses are also easy prey for thief’s and robbers.
• Yet, mud has its advantages like easy availability locally in many parts of the country, saving in
cost and providing insulation which makes mud houses cooler in summer and warmer in
winter.
• Techniques to overcome disadvantages
•In construction of walls, plastering, flooring, etc. scientists have developed several techniquesto overcome some of the disadvantages of using mud as building material.
• Researches have identified many stabilizing agents, such as lime, bitumen, rice husk cement
to be used in mud construction to improve bearing strength.
• In many countries, especially African countries, materials such as cow dung, plant juices,
extracts from boiled banana steams and bean pods are mixed with mud to make it water
repellent.
• The national building organization, by way of research, has found that mud walls built with
sun dried bricks or using rammed earth construction method perform better than those built
with other techniques.
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Technical aspects
• Adobes can take an infinite number of shapes and sizes which are utilized for a variety of
techniques.
• The bricks are locally produced and the quality can be monitored.
• Neither construction workers with special skills nor special equipment is needed.
• It is a low cost technology because the bricks can be produced by the home owners
themselves under guidance or supervision.
• Raw materials are available almost anywhere in the specific region.
• The design for a basic house is of a modular system with 4 extension possibilities.
• The adobes should be made with improved seismic performance to resist disasters such
as earth quakes by having a check on the brick composition, and quality of construction, a
robust layout and improved building technologies.
• Precautions must be taken to ensure durability of construction such as wide eaves to
protect walls from rain, solid foundations to protect walls from ground moisture and gutters
to prevent splashing.
• Mud plaster is a satisfactory, cost effective, long lasting traditional finishing medium for
adobes.
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• Environmental aspects
• The house does not heat up easily in warm and humid climates.
• Provides resistance to sandstorms and flooding.
• It is ecologically sound and provides stable alternative technology.
• Materials are recyclable.
• It has excellent thermal and acoustic properties.
• Production does not require any energy consumption.
• Socio-cultural aspects
• Provides good opportunity for local capacity building.
• The beneficiary can get involved in the construction work as the technology is very
simple, creating community mobilization opportunities.
• The house can be designed according to socio-cultural requirements, beliefs etc.
• Economic aspects
• Adobe is a low-cost, readily available material.
• Only little or no transportation cost is involved.
• Adobe is appropriate in areas which are labour rich and capital poor because it is
labour intensive, using local material and simple tools.
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Advantages
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Advantages
• Well designed mud brick buildings look
warm and inviting
• Mud brick manufacture utilises the natural
material of the site and requires no artificialadditives (except bitumen when that is used
as a stabiliser).
• Mud brick manufacture need not require
mechanical equipment and has negligible
embodied energy if material sourced at site.
• The technology is very simple and almostanyone can build in this material.
• Because they have high thermal mass mud
brick buildings are very effective in reducing
temperature swings in climates where the
daily temperature swings are large. When
combined with good passive solar design
mud brick houses are extremely
comfortable, warm in winter and cool in
summer.
• Unreinforced round mud brick buildings
have good earthquake resistance.
Disadvantages
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Disadvantages
• Unreinforced rectangular mud brickbuildings perform extremely poorly inearthquakes. In the 2003 earthquake inBam, Iran many mud brick buildings werecompletely destroyed.
• Note however that Dominic Dowling of UTSin Sydney has devised a system of reinforcing rectangular mud brick buildingswith bamboo to withstand earthquakes.
• The insulation properties of earth walls is
not good (R approximately 0.5 m2K/W for250 thick walls) and therefore thermalperformance is poor in very hot or very coldclimates with small daily temperaturefluctuations.
• Local soils are not always suitable for use orstraw or bitumen may not be readilyavailable.
• Can require frequent maintenance if exposed to extreme weather unlessstabilised or rendered.
• Drying of bricks prior to laying can be aproblem in areas of high humidity.
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How To Build an Earth Block
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For further details please see “Introduction-to the-production of CSEB” provided by your tutor.
How To Build an Earth Block
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How To Build an Earth Block
• Sift the Clay
• The soil itself is the most important ingredient in earth block construction.
• Then the soil is sifted through a 3/8 wire mesh.
• Stabilize the Clay
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y
• The mortar is mixed at the building site.
• Although clay is essential in earth block construction, blocks that contain too much
clay may crack. In many parts of the world, builders use Portland cement to
stabilize the clay.
• The lime used to stabilize the clay must be fresh, Hallock said. Lime that has turned
gray is old. It has absorbed humidity and won't be as effective.
• The ingredients are placed in a large concrete batch mixer that spins at 250 rpm
• The more thoroughly the ingredients are mixed, the less need there is for
stabilizer. Later, a smaller mixer (shown here) is used to combine the mortar, which
is also stabilized with lime.
Compress the Clay
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• The earthen mixture is compressed into building blocks
• A tractor removes the earth mixture and places it into a high-pressure hydraulic
ram.
• This machine can make 380 compressed earth blocks (CEBs) in an hour.
• A standard CEB is 4 inches thick, 14 inches long, and 10 inches wide. Each block
weighs about 40 pounds.
• The fact that compressed earth blocks are uniform in size saves time during the
construction process.
• Oil is also saved because each hydraulic ram machine consumes only about 10
diesel gallons of fuel a day.
Let the Earth Cure
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Let the Earth Cure
• The compressed earth blocks are wrapped in plastic.
• Earth blocks could be used immediately after they are compressed in the high-
pressure hydraulic ram. However, the blocks will shrink slightly as they dry.
• Workers set the newly made earth blocks on pallets. The blocks are wrapped
tightly in plastic to preserve the moisture.
• The month-long curing process helps strengthen the blocks.
Stack the Blocks
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• Mortar should be used sparingly on CEBs.
• Compressed earth blocks (CEBs) can be stacked in a variety of ways. For best
adhesion, the masons should use thin mortar joints.
• The masons should apply a thin but complete layer to the lower course of the blocks.
• The slurry should still be moist when the masons lay the next course of blocks.
• Because it's made from the same ingredients as the CEBs, the moist slurry will form a
tight molecular bond with the blocks.
Reinforce the Blocks
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• Compressed earth blocks (CEBs) are much stronger than concrete mason's blocks.
• CEBs are also thicker and heavier than concrete mason's blocks
• Once the earth blocks have been plastered, these walls are sixteen inches thick.
• Steel rods extending through the mason's blocks provide added strength.
• The compressed earth blocks are wrapped with chicken wire and securely
anchored to the interior walls.
Parge the Walls
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• The earth block walls are parged with lime plaster.
• Next, both interior and exterior walls are parged .
• They are coated with lime-based plaster.
• Like the slurry used to mortar the joints, the plaster used for parging bonds with
the compressed earth blocks.
Insulate Between the Walls
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• The compressed earth block walls have been reinforced with wire and parged with
plaster.
• The houses appear to be attached, but there is actually a two-inch space between
facing walls.
• Recycled Styrofoam fills the gap.
Add Color
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• The plaster-coated earth blocks are colored with a lime-based finish.
• Tinted with mineral oxide pigments, the finish produces no toxic fumes and the
colors do not fade.
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