Natural Building Colloquium

7/27/2019 Natural Building Colloquium

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5.09.2012 Natural Building Colloquium

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Colloquium:• Introduction

The Context:• Natural Building

• The Buil ding Codes

• Societal Impact Matrix

• Return of The Village

• Habitat For Humanity

• Earthmother Dwelli ng

• Intuitive Design

• Curves of Breath & Clay

• Feng Shui

The Art:• Overview of Techniques

• Nature, Earth & Magi c

• Hybrid House

• Barefoot Architecture

• History of Cob

• Cob Q & A

• Natural Composites

• Compressed Earth B locks

• Adobe Oven

• Earthen Floor

• Earthbags

• Honey House

• German Clay Building

• Straw-bale Dome

• Earthen Plaster & Ali z

• Natural Pai nts

• Bamboo

Technology:• Solar Distiller

• Solar Water Heater

• Composting Toilets

• Watson Wick

• Solar Ovens

Home Page:

networkearth

Compressed Earth BlocksWAYNE NELSON

At the inception in 1976 of Habitat for Humanity International, a

major provider of housing for the world's poor, one of the first

decisions made by the board of directors was to use locally-

available materials as much as possible. This choice is the basis

of a more sustainable building system, which is empowering to the

people of the community, and better for the environment. In my

experience teaching in Africa and elsewhere we have often used

Compressed Earth Block.

Compressed Earth Block (CEB) is one name given to earthenbricks compressed with hand-operated or motorized hydraulic

machines. There are hundreds of types of machines. Some of

these are designed with simple levers which are easily

manufactured in local machine shops, so that in many countries

they have seen widespread use. Other presses contain a variety of

compression mechanisms such as cams, hand-operated hydraulic

assists, toggles and motorized hydraulics. As these presses are

more complex and expensive, they have had less frequent use. In

many areas of the world, proper materials are available for making

CEB, and thus this type of block may be a better choice than any

other building material. The choice to use CEB is dependent on

several factors, including culture, labor force, and most

importantly, the preference of the homeowner.

Hand-operated presses have been used for many decades. Before

that, and still today, some people make the blocks by beating soil

into a wooden mold with a stick. "Rammed earth" is a similar

process, in which case a structure is made as one continuous

mass of compressed earth.

Modern equipment, with hydraulics driven by diesel, gas or electric

motors, may be useful in urban areas or for large multi-house

sites. However, the difficulty of using motor-driven equipment for smaller and more rural projects is hard to grasp until you have lived

in a remote village situation. People in these situations are often

the ones that need the most help with improving their housing, and

compressed earth block can be one of the solutions to their

building needs. However, one must be aware that significant

problems with maintenance, expense of fuel and spare parts, as

well as the tools and expertise needed to repair and maintain the

presses, have been experienced by many local builders who have

tried to use these machines without understanding their proper

place in the local economy.

Advantages of Using Compressed Earth Blocks

Advantages of CEB include: uniform building component sizes,

use of locally-available materials and reduction of transportation.

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. Such

modular elements as sheet metal roofing can be easily integrated

into a CEB structure. The possibility of using such components

can often improve the overall quality of the structure as well.

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 to import materials, fuel and replacement

parts. The earth used is generally subsoil, leaving topsoil for agriculture. Building with local materials can employ local people,

and is more sustainable in times of civil unrest or economic

difficulties. People can often continue to build good shelters for

themselves regardless of the political situation of the country.

The reduction of transportation time, cost and attendant pollution

can also make CEB more environmentally friendly than other

materials. Most of the time, soil for CEB can be found on site or

within a short distance. In most of the world's economies, the most

cost-effective transportation is often that provided by people or

animals. In Ghana, for instance, 3' x 5' wagons were built with oldcar wheels and tires. It was less expensive to have a few people

move 20 cement bags, or two 55-gallon drums of sand in one load

with this wagon for two miles up- and down-hill than to hire any

motorized form of transport such as a bus, truck, or tractor with

wagon, because all the latter are dependent on fuel and parts

purchased from economies outside that of the local community.

Innovations in Compressed Earth Brick

Over time, innovation in CEB manufacture has included changing

the original shape from a solid rectangle to one incorporating holes

or grooves in the blocks to allow for the use of steel or bamboo toresist earthquakes. Another innovation was to create interlocking

shapes that don't need to be laid in a bed of mortar, and U-shapes

or tapered bricks for use in reinforced lintels or arches. Floor tiles

and roof tiles can be made on some machines. Sometimes the

press has been used to make bricks which were then fired in a

kiln, although once fired they are no longer referred to as CEBs.

The interlocking shapes of these improved bricks can help to

reduce the skill level needed for homeowners to build their own

homes. In addition, several layers of blocks can be placed in the

wall at a time. A supervisor can then check that the wall is straight

and plumb before giving the OK for mortar to be poured inside the

hollow blocks to lock them together, thus eliminating the small

openings between blocks which would otherwise allow for air

infiltration.

Materials on some of the different machines are available through

the European development agency, GATE, although I wouldn't rely

on their comparisons of speed and ease of operation. Some

presses are shown in their Appropriate Building Materials book by

R. Stulz and K. Mukerji. In addition, the earthbuilding organization

CRATerre in France and the community of Auroville in India have

experience with many types of presses.

My favorite hand-operated press is the "TEK" from University of

Science and Technology in Ghana. The TEK ram is simple and

inexpensive. There is a similar French machine which is great and

simple to operate as well, but it costs ten times as much. Both





machines create a CEB block using only one operation. The lid is

tripped automatically with the handle motion so there is no

separate operation to close the lid or lock it, nor the need for a

second lever to pull or push. I like the size of the brick from this

press as it is bigger than most. It measures 30 cm long x 23cm x

15cm (12" x 9" x 6"). I have used the 15cm dimension for the width

of the wall, but wall thickness could be made to any of the three

dimensions simply by turning the block. Bigger blocks means

fewer elements that I have to move around as I build, therefore

speeding up the process.

I like to reduce the amount of material I have to use to make a

brick, so "frogs" which dimple the body of the brick as it is pressed

are nice. I have also reduced the thickness of a brick by putting a

one inch board in the bottom of a 6" mold. This simple operation

made my wall 5" thick, still sufficient for a small simple, decent

house (such as Habitat for Humanity builds, which is affordable to

most people in the world).

The Earth Mix

There are several simple publications on select ing earth and using

a press. VITA has a good one, as do some machine

manufacturers. The UN has simple soils testing information, and

many universities can help test soils as well. In addition, soils

engineering has been done in labs for road-base materials which

are basically the same materials that are good to use for walls,

floors and arched roofs. However, there is nothing like experience

to tell how the soil will work, and many indigenous folks know local

soils that are good for different purposes such as building. If you

are on your own, look at cuts at the roadside or river bank to see

how different soil types resist erosion. If the soil resists erosion

well, it could be a good building material.

There are two simple soil tests that I like to use to determine the

proper soil mixture. For the first test, fill a clear jar with straight

sides half full of soil and then three quarters full of water, adding a

pinch of salt. I like to use a plastic peanut-butter jar with a lid. Cap

it tight and shake it up until all is in solution. It is good to let it

soak for a few minutes and then shake the solution again to get it

mixed well. Normally, layers of different particle sizes will form as

it settles. This may take a few minutes with the salt added or a few

hours without salt. The large particles on the bottom of the jar will

be sand, then silt will settle out and finally a clay layer will form on

top. Mark the height of each layer to get a rough calculation of the

percentages of each material. With hand presses 10% clay is a

minimum amount to make strong blocks. To see the clay layer

separately, open the jar and let the sample dry. The clay is a

binder, so it sticks together and will curl up and shrink, pulling

away from the layers below. Think of a mud puddle drying after a

rain with the clay curling up on the top as it dries.

The other test is to build a form 2' long and 1.5" wide x 1.5" tall

that is then filled with moist soil. Wait a week, letting it dry in the

shade. Once the soil sample is dry, you will notice a gap between

the end of the clay body and the end of the box. This gap showshow much the clay shrinks. Acceptable shrinkage is less than two

inches and preferably 1/4" or less. The less shrinkage the better

the soil. If you have a lot of shrinkage, indicating a high clay soil

(over 25% clay), you might add sand to make a better mix. A soil

with a very expansive clay may be rejected after this test, but soils





in close proximity or lower in the ground may have less expansive

clays. When you find a good soil, it is important to keep testing

the soil even after you start to make bricks to insure quality.

The stability of the clay can also be observed by placing the brick

in a bucket of water after it is compressed, and seeing how quickly

the clay will expand and explode the particles from the brick. If the

brick is stabilized and well cured, placing the brick in a bucket of

water, stream or lake can be a great way to show its water

resistance to those who might doubt that soil can be used to builda good house.

Stabilizers for Compressed Earth Brick

Stabilizers such as cement, gypsum, lime and the liquid types

have been used in the body or on the surface of the bricks.

Sometimes it is less costly to make a soil block with no cement

and then use cement for the mortar joints and a cement plaster

which adheres to the mortar joint. (Cement plaster doesn't stick

well to unstabilized earth bricks, so the mortar joint is used to hold

the plaster.) Natural earth plasters with natural additives can alsobe used on unstabilized walls. These plasters may require

maintenance on a regular basis, which is similar to giving your

house a fresh coat of paint.

When using cement stabilizers, it is very important to cure the

cement by keeping the brick moist. This may mean watering twice

a day for a couple of weeks and covering the wall with plastic or

leaves to keep the sun and wind off and the moisture in. Cement

cures with water, so letting it dry too quickly, especially during the

first week or two of curing, robs it of its strength. Blocks without

stabilizers should also be dried in the shade to avoid excessive

drying around the edges which may cause cracking.

When mixing the stabilizers with the earth, it is important to make

sure they are mixed completely, especially when using smaller

amounts. Using a 3% cement-by-volume ratio takes a lot of mixing

to get the cement distributed thoroughly. I recommend using a

garden rake, although most of the time the stabilized earth is

mixed with shovels in a similar fashion to mixing concrete. I prefer

the rake with its many tines because it mixes more thoroughly,

breaks up particles of dirt, and, if water needs to be added to bring

it to the right consistency, spreads the water through the mix more

easily. I find moving the rake back and forth through the mix easier

and faster than picking it up with a shovel and turning it over. I can

feel when the moisture content is correct more easily with the rake

by how it feels when it is moved through the mix.

Being a person who is always looking for an easier way to do

things, bigger, simpler and faster are things I like. I've heard it said

that if you want to see how to get something done easily, watch

how a lazy man does it. I would caution that you may have to

modify a lazy man's way a bit to get it done right, but I think there

is truth in that statement which can lead to simplified work

processes.

Moisture Content

One of the most unique things about making CEB is the moisture

content. It is common to find people making the mix too wet. The

moisture content of the proper mix is so minimal that it never really





seems wet. People often have experience with mixing concrete or

adobe, the moisture contents of which are way too high for CEB

mixtures. One simple test is to take a handful of CEB mix and

squeeze it into a ball as tight as you can. If the mix stays in a ball

when you open your hand, the moisture content is good. If it falls

apart in your hand you need to wet it more. When the ball stays

together in your hand, drop it from your waist to the ground. If it

sticks together or breaks in only two or three parts when it hits the

ground, it is too wet. In this case add some more dry ingredients,

keeping the ratio of soil to cement equal to your original mix. If itbreaks into dozens of pieces, add a little water. It is common to err

at this point by adding too much water. The little water you add will

take a lot of mixing to get it thoroughly into the mix, so don't rush

at this point by adding more water than needed, because it is a lot

of work to dry the mix out again.

Why is it good to use as little moisture as possible? Minimal

moisture content results in better strength, water resistance,

durability and thermal mass in the finished block. An

understanding of the structure of soil is helpful in grasping its

interaction with moisture. Imagine that we magnify the size of theparticle and look at it. If you look at a pile of stones you see space

between the stones. This is similar to how sand particles look. If

you try to compress the pile of stones, they really don't compress

because one rests on top of the other. The spaces are similar to

those between the sand particles in a CEB. We want to fill the

spaces with clay because the clay acts to bind the sand particles

together. Sand does not have the characteristic of sticking

together well when it is dry, but the addition of clay binds the sand,

helping the block keep its shape. To get clay to stick together

well, it is first saturated with water. Mixing the wet clay helps the

clay particles to align with each other. Because clay particles are

flat, rather than round or angular like sand, they will stick together or to sand like wet paper.

I like to pull a few bills out of my pocket and toss them in the air to

give an example of how dry, loose clay particles act. They all fall

loosely away from each other. I pick up the bills, laying one neatly

on top of the other, and wet them with water, press them together

to get any excess water out, then throw them in the air again. Now

they fall as one unit and remain stuck together. I can let them dry

and toss them in the air again they again fall as one unit. In a book

that has gotten wet, to open the pages you almost have to take

them apart one by one. This is how wet clay particles bind

together and bind the sand particles together as well.

When a block machine compresses a block, it reduces the volume

by 30%. It does this by mechanically aligning the moist clay

particles, removing the air pockets and sticking the clay to the

sand. If too much water is in the mix, there will be more air space

between the particles when the brick dries. This reduces the

strength and thermal mass, and makes the surface more porous

so it is not as resistant to water and scratches. If there is more

clay than is needed to fill the spaces between the sand particles,

the block becomes weaker because clay compresses more than

sand, especially when wet. However, weaker earth walls can befine too, as we know from the use of cob and adobe. In these

cases the thickness of the wall may need to be increased to carry

the same roof loads.

Production





How fast can you make blocks and begin building? Efficient

workers using hand presses can make 500 a day, resulting in one

week's work for the walls of one house. I've done 80 blocks in a

day by myself, so you might plan on five to ten people making 500

in a day, or several machines working at the same time in order to

make all the bricks for a house in a day. A hydraulic machine can

make all the blocks for a large house in a day, if you can feed the

soil to it quickly.

After they are pressed, blocks can be set aside to cure. When

using the hand-operated presses, it is not recommended to stack

them on top of each other the first day, and remember to handle

the blocks as little as possible so as not to knock off the fragile

corners. The next day the blocks can be stacked several layers

high to make room for the next batch to be set out. It is possible,

however, to place bricks directly in the wall, either dry-stacked or

mortared, so with enough people and the right equipment the walls

of a simple house can be completed in a day. Some mechanical

soil crushers, sifters and mixers are available to speed the

process. As with all repetitive processes, speed can be increasedby thinking through the steps and organizing the process

efficiently, thus avoiding machine down time.

Most people who build with earth find it quite enjoyable. It can be

just plain fun to make your house from the earth under your feet.

Enjoy the earth God has given us.

Wayne Nelson works with Habitat for Humanity's Department of

the Environment and is an international provider of construction

information and training. Trained as a carpenter and builder, he

has particular experience with creating shelters with compressed

earth blocks in Africa and other countries.

Construction and Environment Resources

Habitat for Humanity International

121 Habitat St., Americus GA 31709

ph 912-924-6935

www.habitat.org

[email protected]

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