| FEED-BACK |
| VERSION FRANCAISE |
| Constructible Earth |
| Daub |
| Mud-woodchips |
| Earth Rendering |
| Working Green Wood |
| Chestnut Wood |
| Coppiced timber |
| Fibres |
| ECOLOGY |
| BEN'S WORK |
| WORLEC |
| Hint: If you skip from bold text to bold texte you can get a complete summary of all the arguments and information that I present. |
Natural Construction Materials
Natural
does not equal ecologically sustainable
nor pure; we require
a scientific and not
a moral judgment to evaluate them.
Ecological considerations :
-
Their use is not necessarily ecologically sustainable nor without any risk for the environment or our health. They are obtained from the environment and the locality and the techniques employed must be considered.
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Strip-mining is equally disastrous whether used to extract natural materials for direct use or for manufacturing construction products such as baked bricks or cement.
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Their extraction on site provides a hole which can be useful as a cellar or a water hole for fish, ducks, irrigation or swimming.
Remember Permaculture?
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Cutting out virgin forests is not sustainable but managed coppicing can provide all the construction timber that we need.
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Fibres and modifiers can be harvested from organic agriculture.
Ecological
sustainability implies using natural
materials with minimum
processing.
Health considerations :
-
Fine particles are harmful whatever their source or chemical composition.
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Large falling particles are often fatal.
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Fine fibres irritate the lungs and are not expelled.
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Natural modifiers are not often edible nor good for our skin.
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Allergies are reactions to proteins which I guess are all natural. The most important one found in our houses are acarians which eat skin particles which we leave in our living spaces, but we are sensitised by complex organic compounds, frequently emanating from the chemical products in our paints, varnishes and plastic materials.
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Burning natural materials always produces harmful gas emissions.
Ecological
sustainability implies
the safe
and healthy
use
of natural
materials.
Solutions:
Tradition offer us many solutions and science gives us the tools to research them. The problems are rarely as serious as those associated with the use of manufactured products with which we have, typically, little long-term familiarity.
Advantages:
What are they :
Actually they are few and fall logically into three categories :
| Minerals |
Structural
organic materials |
Organic
modifiers |
| Particles |
Composites |
Liquids |
| Gravel,
sand, silt, clay |
Wood,
bamboo, bone, leather, fibres |
Linseed
oil, egg white, buttermilk, urine, excrements, sap,resin, wax, grease,
blood |
Minerals :
~~~~They are distributed
everywhere.~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sedimentary rocks provide building
stones and slates.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gravel:
Gravel is the stuff of avalanches and sweep all before them. They pound and crash in the water. They are the mortar and pestle that created the sand and silt. On a slope they are scree - very dynamic, dangerous and sometimes exciting - scree jumping.
They are deposited in valleys and form large flat beds; which gives us the clue as to where to find them and how to use them.
Sand:
The
world of sand is a world of tumbled rocks, full of unstable cavities.
Water floats the grains into place to form a compact mass. Dry,
it flows like water and forms large puddles, filling the hollows.
It is grains of silica and quartz, sometimes with pulverised limestone, measuring between 5 mm and 0,06 mm. The grains are visible with the naked eye. Sea sand, being round, is useful for masonry, but is not so good for rendering. River sand is sharp and generates open structures that leave more space for the silt and the clay to contribute to the cohesion. The structure of sand stabilised in this way has improved resistance to compressive forces.
Silt :
The
world of silt has been tumbled for millenniums. It is inhabited
by small, round, cuddly particles. Water carries them to fill the
cavities in the sand where they form a network of small groups which consolidate
the material.
This is really fine sand which gives earth a loamy texture, composed mainly of silica and quartz particles of between 0,06 mm et 0,002 mm dia. We see it as a layer of particles too fine to be seen separately. Its contribution to the earth's stability is due to it's internal friction by the filling the openings in the sand. Too much makes the earth more friable and crumbly.
Clay :
The
micro fine is a slippery world. We can feel it with our fingers.
Water lubricates it and leaving, allows it to repose in electrical equilibrium.
Dry, it shrinks back on itself and becomes hard and stiff.
This is composed of particles (or micelles) of hydrated
aluminosilicates <2µ (0,002 mm). Because they have
multi-layered molecules they have a specific
surface infinitely larger than that
of bigger grains going from 10 to 800 m²/g. We can consider
2 groups of clays. Those that hardly
swell with water,
represented mostly by kaolinites, and those which swell,
represented in our region mostly by lime-clay
compounds or montmorillonites and illites. The presence
of clays that swell
is indicated when the water in
which they are in suspension remains
cloudy for more than 10
minutes. For building we
need stable materials;
we therefore seek to maximise
the kaolinites.
Electrostatic forces
which bind the clay particles
ensure in large measure the cohesion of the earth.
Constructible Earth : (What some of you, strangely, call mud?)
This is a mixture
of sand,
silt
and clay
approximately in the proportions of ½,
1/3, 1/6, without humus and colloïdes other than clay;
the ideal mixture is a structure
of large grains, with the spaces
between filled by smaller and
smaller grains. The mixture
is held together by a thin layer
of clay and water
surrounding each grain. Gravel will be present according
to the proposed use, medium
gravels being acceptable in a beaten
earth pavement, (often built on a bed of large
gravels left with an open structure).
Water :
The reactions between the water and the materials that make up the earth, including the impurities that may be present, explain all the qualities and imperfections that we can detect in our construction.
- Rainwater is better due to the intervention of OH-ions in the liaisons between the clay particles which become more sticky. This effect can also be obtained by adding defloculants, such as soda and sodium silicate in the proportion of 0,1 to 0,4 % of the clay, or by replacing the water completely with humic acid , tannic acid or horse's urine. These substances allow us to use less water, give less shrinkage and permit rapid drying. The act of mixing distributes the clay particles more or less equally within the mixture. The water penetration takes a certain time, which can be reduced by fine grinding. Dry clay is rigid like concrete. Adding water gives us a plastic material which we call mud or daub. More water gives us a liquid mud or slip, less and less sticky up to saturation point when it becomes cloudy water.
- Up to saturation, adding water to sand makes it more cohesive. The silt acts in the same way. This reaction, along with that of the clay which makes it more slippery, gives us the consistency of mortar. The combination of liquid mud or slip, sand and silt makes mortar.The humidity of the sand and the water in the slip must be taken into account to obtain a mortar of good proportions with a good consistency.
- Salts present in the water or in the earth can cause efflorescence which damages lime, cement or plaster but not earth renderings.
Stabilisation:
Stabilisation is not always necessary but can be useful in difficult circumstances. It can help to improve resistance to erosion, to distortion or to humidity. We can add 20 to 30 kg of fibres to each m3 of earth. Animal manure, ox blood, rye flour, sap and oxidising oils are some of the modifiers used as stabilisers. The use of mineral stabilisers such as lime and cement are only useful in particular cases because they are hydrophilic, they attract water and are more cold to the touch than earth.The sand that François found on the river bank was sufficiently well dosed with clay to be used as it was for rendering his wall
Daub:
Daub is crude constructible
earth used in a malleable
state (and the name of the act of manipulating it), mixed by hands or
by feet. It is traditionally mixed with a little straw
or cereal husks and is used to
fill timber frames or to make
adobe bricks.
The earth is improved
by adding sand or clay
to obtain the optimal proportions (1/2
sand, 1/3 silt, 1/6 clay ).
All fibres
are good once dried. We
add from 5 to 10%
to the earth to stabilise
the daub. The optimal
length is found to be around the thickness
of the layer in which it is to
be employed.
The daub
is made in a pit or a specialised
mixer.(Those for mixing bread dough work well). It is too
stiff to be mixed in a concrete
mixer. It has good resistance
in compression. It is not
very insulating, like stone
or baked bricks, but it has a
good thermal capacity.
It's major quality is its power
to maintain the hygrometry
of the surrounding air within
the comfort zone at all likely
temperatures.
Add water
to daub and it becomes mortar
which can be mixed in a concrete mixer
and can be applied with a trowel.
With round sand we lay bricks,
stones and tiles.
Sharp sand is for rendering.
(I am not familiar with English Documentation -help!)
Mud-woodchips:
The mixture mud-woodchips is a composite which contains a lot of granules, shavings or fibres, typically 90%; covered with a little mud (clay). The woodchips come from woodworker's waste.It is available in prefabricated panels, see Akterre, and is used to make lightweight earth concrete.
Terre-paille is a mixture traditionally used in Normandy, made from long straws, covered with mud. It is mixed with a pitchfork or a special mixer.
Mud-woodchip mixtures can be made in an ordinary concrete mixer. They have little structural resistance. Good insulators, they contribute little to the thermal capacity. They are good acoustic insulators and research suggests that the size of the filler and the weight of earth included influences the frequency of the sounds which are reduced.
Rendering with Earth
Rendering with Earth - application
Mortars for rendering:
Surface preparation :
The adhesion of earth rendering to it's support is mostly due to it's rough texture. The support must be stable, not friable and dust free. If this is not possible, we must provide a mesh of split bamboo, willow or fabric firmly fixed to the support. This reinforcement is necessary at the angles and the changes of the nature of the support. The hydrometry of the support influences the suction between the support et the rendering. A light suction is necessary to ensure the continuity of the liaison between the support and the rendering. Too much suction provokes quick drying, with regions starved of clay and the appearance of fissures. Too much water in the support or in the rendering limits the adhesion. Watering the support should be spread over several days. It is given until the support remains wet but not enough to swell the clay in the support and we wait for it to dry. When it takes from 10 to 20 minutes to dry, the support is ready.
Splash coat :
A first coat of mortar is thrown onto the support. This splash coat, quite liquid and rich in clay, materialises the liaison between the rendering and its support. It insures the conformity with the rough support and presents a rough finish. It is not necessary for a support made with daub. It should be from 2 to 4 mm thick. We wait 2 to 8 days for it to dry completely.
Body coat :
Rehumidified, we apply the body coat, thrown or spread over the splash coat. Being the body of the rendering; it is regularised with the edge of the float to a thickness of 8 to 20 mm to equalise the surface of the support. It can be applied in several layers, the dose of clay diminuing, and is dressed with a straight edge to obtain a flat surface. Without fissures, it is scratched or brushed to improve the adhesion of the finishing coat. It must be allowed to dry thoroughly.
Finishing coat :
This is the decorative
layer, it covers the remaining imperfections. It is less
dosed with clay to prevent any fissures and provides
the colour and the texture.
It should not be heavily
trowelled to avoid any risk of crazing. So finally
we rehumidify and apply this thin coat, 2 to 4
mm thick, with minimum trowelling. It is
also the coat which takes the
wear and might need occasional
resurfacing. We can add up to 5% of fixative.
(see below)
Paint :
Inside we use liquid mud (or slip) to which we add fixatives. These fix the dust and equalise the surfaces. This offers another occasion for decoration. Butter milk, whey, egg-white, sap and oxidising oils are modifiers can give good results as fixatives.Organic Structural Materials:
( in construction )
Wood:
| Habitat - Tradition - Écologie | Training: WORKING GREEN
WOOD
|
| Introduction. | |
| Web Site : http://lorien.free.fr | Author:
Peter Lorien. Date : 15 June 2000 |
Using green wood is a long history
that we have forgotten since the arrival of large mechanical saws.
These cut small sections from large
trees, which although dry remain unstable. To understand this we
know that green wood contains sap and it shrinks on drying.
Sawing wood cuts across the fibres and the drying cannot be regular. Correct seasoning is complex and difficult to achieve.
Green wood is well adapted to being squared with an adze or side-axe because the wet wood is softer.
From each length we take a single piece of wood with the heart at its centre.
We respect the natural form of each length to make our work easier and to make the structure more attractive.
Like that it doesn't move.
The wood obeys a simple rule. C=~2r
This difference in shrinkage means
that we must take precautions to limit and direct the eventual cracks.
- They are limited by slow drying.
- We paint the ends with wax emulsion or bituminous paint to slow down the drying.
- We direct the cracks to weak points that we introduce by means of rebates, grooves or mouldings.
- We
protect the wood with an oxidising oil, in Europe linseed oil, as soon
as possible.
Using traditional joints (except the halving joint in the case of chestnut), allows the wood to shrink and to expand without weakening the stability of the structure.
Coppiced Wood:
Coppicing
is an ancient practice for harvesting
trees known to the Romans. There are coppices
in Europe that have been harvested since the Middle
Ages.Mature trees are felled
and the remaining stump is left
which throws out sticks which
can be cropped; each year
for willows, but every 20
to 35 years
for carpentry timber. The
sticks are selectively
pruned to provide a small number of fine timber
spars.
This production cycle has been maintained for at least 800 years without negative effects, neither for the crop, nor for the environment. The soil mineralisation is improved from year to year by the addition of minerals concentrated in the leaves, having been brought up by ever deeper roots.
Coppiced
timbers are pre-sawn on
the bandsaw and if required hewn
with an adze or a side
axe. It produces spars
from 10 to
20 cm square, often curved
in one plane, but straight in
the other. These I use for traditional
carpentry and
timber-framed walls. I have met some colleagues in the Aveyron
who have been doing this for the last 21 years.
référence : LE CHÂTAIGNIER
UN ARBRE UN BOIS - Catherine Bourgeois - IDF
(I am not familiar with English Documentation -help!)
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CHESTNUT
- The Wood |
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CHARACTERISTICS |
COMMENTARY |
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COPPICED
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The subtility
Straw slides, Pampas grass hooks on.
Fibres:
What fibres can teach us
Contrary to popular belief, fibres
rarely contribute their resistance
to stretching, it is the weak links
between the fibres and the matrix
(the earth), which obliges micro
fissures to go off in all directions
when the material is subjected to external
forces . The micro-fissures
absorb the
energy which would have produced a large
split. The mass doesn't split
apart.
Weakness gives suppleness
that resists better.
This paradox is explained in mechanics
by the transition from the elastic
state to the plastic state.
It is the principle of all composite
materials including (wattle
&) daub.
Daub,
wood,
bone and leather
are among the most efficient and
versatile composites
and they're renewable.