Constructible Earth 
Earth Rendering 
Working Green   Wood  
Chestnut Wood  
  Coppiced timber  
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

  • 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. 

  • 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?

  • Cutting out virgin forests is not sustainable but managed coppicing can provide all the construction timber that we need.

  • 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.

  • Large falling particles are often fatal

  • Fine fibres irritate the lungs and are not expelled. 

  • Natural modifiers are not often edible nor good for our skin.

  • 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.

  • Burning natural materials always produces harmful gas emissions.

Ecological sustainability implies the safe and healthy use of natural materials.


In this page I consider the necessary minimum processing for making natural building materials ecologically and safely. Minimum means less resources, energy, pollution, transport, health risk and more useful life for us and our products.

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.


The major quality of natural materials is their accessibility.  Requiring little energy or processing for their use, more people can employ them for their constructionsDirect access makes us more aware of their environmental and health impact, facilitating the management of potential hazards.  Accessed locally their transport has little or no impact.

What are they :

The fact  that natural materials are traditional does not relieve us of the need to think about  how we extract and use them.
Actually they are few and fall logically into three categories :

Structural organic materials
Organic modifiers
Gravel, sand, silt, clay
Wood, bamboo, bone, leather, fibres
Linseed oil, egg white, buttermilk, urine, excrements, sap,resin, wax, grease, blood

Minerals :

The mineral world is made up of particlesLarge rocks, detached from the Earth by geological and climatic forces are scattered with extreme violence  and and broken into smaller fragments.  These are being buried, compressed, re-exposed, eroded, dissolved, and sedimented. They are ground by glaciers and they descend by avalanche or are carried by rivers.

~~~~They are distributed everywhere.~~~~

Sedimentary rocks provide building stones and slates.


Gravel is the large particles that are the basis of the structure of earth, they are the monsters of the particulate world.

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.


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 renderingRiver 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 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 earthAnimal 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 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.

référence : Traité de Construction en Terre - CRATerre - Parenthèses
(I am not familiar with English Documentation -help!)


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 resistanceGood 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.


wall by Ben & Jeremy P

wall by François et Mark

Rendering with Earth

Rendering with Earth  - application

Mortars for rendering:

They are made with dry river sand (sharp), mixed with  clay mud to the standard consistency  to obtain a mortar which is easily manipulated with a trowel.  Each successive coat  should be less rich in clay than the preceding one and the maximum size of the grains of sand in the body and finishing coats should be less than half the thickness of the coat in question.

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 coatBeing 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 )


Pierre, François and Ben  with our construction after the weekend.


















Habitat - Tradition - Écologie Training:

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.

tronçons avec coeur

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

                                            circumferential shrinkage (C)                                      
radial shrinkage (r)

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!)




  • Density .........0,55 to 0,75
  • It floats!
  • Medium weight.
  • One person  can carry a beam
     3 to 4 metres long.
  • Medium hard.
  • Resists scratches ex. Floorboards.
  • Low shrinkage.
  • Easier split management.
  • Good mechanical resistance in flexion and compression.
  • Excellent wood for joinery and carpentry.
  • It splits easily.
  • Used for split bands, shingles, stakes and fence posts. Take care with the joints used in carpentry.
  • Easy to work.
  • Less wear on tools and your back.
  • The heartwood is resistant to insects.
  • Unlimited life if dry and non infected.
  • It has little sapwood.......5 to 7 mm.
  • Little waste with squared spars.
  • It resists bad weather.
  • >10 years - base in water.
    60 to 120 years - outside, base dry.
  • It resists well to insect attacks.
  • Take precautions when felling and for splits that offer egg-laying sites.
  • It resists well to fungus attacks.
  • Subject to poria above 20% relative humidity .
  • Colour mid-brown.
  • Enriches towards yellow on aging.
  • Closed texture.
  • It shows a patina after few years and takes all kinds of finishes.



  • Dimensions too small for easy sawing of useful pieces.
  • Dimensions ideal for beams and posts normally used in traditional carpentry.
  • Sinuous form  in one dimension makes it difficult to use for contemporary carpentry.
  • Easy to incorporate in traditional carpentry.
  • Tendency to  circumferential splitting.
  • Without importance for squared timbers.

The subtility

Straw slides, Pampas grass hooks on.


Fibres employed in earth construction are of all kinds.  Straw, hay, pampas grass, chaff, linen waste, hemp, nettles and woodchips are all useful.  They bring suppleness and resistance to the composite that contains them (see below).

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.

Modifiers :

( in construction )