Getting a feel for Light Earth


by Peter McIntosh

What I find exciting about natural building is that there are as many ways of using available resources as there are cultures around the world. No absolutes in terms of technique, consistency, design and use of materials exist. People approach similar decisions based on their physicality, life experience and imagination. It is always interesting to me to observe how people I teach and work with approach the material and I try not to prescribe my methods of doing things on people before giving them a chance to display their natural ability or cultural diversity. The world will be a poorer place if natural building became as regimented as the conventional building industry can be. Natural building is not a one size fits all scenario. It can’t be as the materials always vary depending on what is at hand, from rock to wood or a multitude of earths. What works here may not work there because the earth changes or the type of timber in your area is different and has different uses. What this affords us, is to become more engaged with the material and not reliant on books and building codes. There is what works and what does not, and a world in-between.

I have discovered for myself a range of techniques that work and have come to understand that technique is as important as knowledge. Little things become as important as the big things. Just how you apply a plaster coat is as important as the recipe for the mix. A material may not work in a particular way, but if you change the technique, add more or less water, put the material under pressure or just simply allow it to breathe you may have success. When I feel ready to abandon an idea that I thought might work, I find myself wondering what I am missing, because you can be sure that others with the same materials have found a way.

Combining the same materials in different ways has different outcomes in terms of structural ability and how they perform thermally. Adding just a little straw to a mud-brick will double its insulating ability and increase its tensile strength. That is not to say you want the material to become more insulating; you may want it to be a heat-sink, to radiate energy or simply just lighten the material up.

A good example of a material that offers both good insulation and a solid feel, while not being so heavy, is a mixture of straw and clay. Or, what I call Light Earth. This technique uses a common practice of placing the material in a simple brick mould and has many other uses too, from insulation in roofs to the walls themselves. It can be shuttered in situ or simply stuffed into spaces, made into boards for the ceiling or bricks.

One method of making Light Earth that I have found particularly easy is to do is to make a circle out of straw bales and lining it with plastic to form a dam.

1_Building a dam

The dam is filled with water about a quarter of the way, after which you can begin adding clay.

There is no exact recipe and a little experimentation is required. The more clay you add the thicker the ‘soup’ will become and the denser the resulting bricks. The dryer the clay is when you add it the better because it then dissolves quicker when added to water. Powering the mixer with loads of feet works best and I have a hard time stopping folks from having a clay bath during courses. Once all the clay has dissolved it’s time to add the straw. A whole straw bale is mixed in using the same method, although this stage of the recipe requires a little more effort.

2_Mixing the clay soup

Once all the straw is thoroughly coated with clay it is removed in heaps and placed on the side of the dam to drain back in any excess liquid. The mixture looks like a bunch of wet straw and not a heap of mud.

3_Extracting the material

This wet straw is then pushed into a mould with care taken to avoid layering. If the block is to be used as a structural element, for example a wall, the soup needs to be more dense so that all the gaps between the straw are filled with clay, otherwise its fine to have some gaps. Scoop any excess clay off of the top and return it to the dam.

The block moulds may be any size and can be as thin as 50 mm and one meter square if they are to be used for making a ceiling, just as you would use with conventional materials. The blocks below are 300 mm by 300 mm and 170 mm deep. A huge advantage is that Light Earth blocks are less than half the weight of a traditional mud brick and with the added advantage of all that insulation. Of course, the weight and thermal conductivity will depend on the amount of clay you added in the first place. As a rule of thumb the material approaches the insulating ability of a straw bale wall when it is 200mm thick.

4_Material in brick mould

Keep adding straw till the clay soup is used up.

These blocks are practically indestructible and survive repeated dropping with no effect. They do however take longer to dry in the sun than a mud brick and a good run of clear sky is essential. They take around 3 days to dry sufficiently before they can be turned on their side to speed up drying, depending on the weather. After about a week they can be stacked with gaps in-between the bricks to finish the process off and covered while stored to protect against the rain.

To conclude, Light Earth is a very versatile material with so many applications just dying to be tried and it’s a load of fun to make. I wonder what would happen if you threw a few kids into the mix as well?

Photos 1, 2 and 4 were taken during a Natural Building Course at Berg-en-dal, which Peter McIntosh co-facilitated with Neil Smith.

Photo 3 was taken at the Tara Rokpa Centre in Groot Marico, a Buddhist retreat where Peter was involved in the building along with architect Paul Marais.

For more information on the courses that Peter McIntosh is involved with please visit our Events page.




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1 Comment


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