Building with earth

Earth. That stuff all around us. The skin of our planet, residue of incalcuable eons of rocks, trees, bugs, fungi and a vast array of other living things squishing together to make this medium for life itself.

I've always thought of it as something we use to grow plants in, or on building sites we move it out of the way to make room for "modern" building materials - cement foundations, brick walls, cement-based plasters and the like. But how about actually building our houses with earth?

Mud huts in Africa spring to mind, or cave-like domes to keep the evening coolness over scorching day, in arid Arabian deserts. But what about here in chilly Europe with our incessent rain? Is it even an option?
It seems so: Ken Neal showed us how with his cob-house in the South of England. Amazing: just add straw and stamp it down, and up the walls soared. Ken's a cob-maestro from those parts, and says that this type of building was normal in times past, in Europe since the 12th century... His cob-house shown here on the left, detail below on right.

Cob houses are one of so many ways of building with earth, the mind boggles at how little we knows about it. OK, there is a small but growing number of builders and crafts-people out there who are working with natural building materials. But the mainstream building industry is almost completely unaware of these options. As I happen to live in a modern society I want to know which other earth-building options there are that might be suitable, in our temperate climate.

OK so there's earth-bag building, brought to public recognition by Nader Khalili of the Cal-Earth Institute. These links show it all: basically a way of making domed buildings with circles of earth in bags. Plastered inside and out with more earth, or a bit of lime for more rainy climes.

Rammed earth is another one, used a lot in the South of Portugal. Also used by the CAT in Wales in a big scale for their new "institute for sustainable education". I've heard it is really labour intensive, like cob buildings, so maybe not that suitable for our renovation where we are surrounded in granite rock. The point about rammed earth and the bagged-wall system is that they offer huge thermal mass, like a house built from rock does: cool in summer, warm in winter (as long as you've got a nice stove or something warming it up). This does not mean it has insulative capacities: unless you put something with fibres and air-gaps in it, like straw.

In fact because rock and wood is readily available here, and straw bale too (nearby Ourense in Galicia). We're thinking of using straw for any new extensions, to be covered outside in a lime render, internally with earth plaster. Which bring us to the other application of earth in building: as a plastering material. (In this case, the straw provides mega insulation, the plaster lends some thermal mass, if you slap it on thick enough).

Somehow, over the last 100 years or so of industrialisation, we have seen cement-based plasters taking over the internal plastering show. This great book gives a full summary of all the possibilities available to us, from clay, gypsum, to straw-clay and so on.

From this book, being at CAT, our own experiences and so on, here's a few reasons why I think earth plasters are so much better than cement:

1. Beathability: cement plaster and walls don't breath, so it's like living in a plastic box unless you have a really well built and managed ventilation system. Earth (and lime) walls allow vapours out but stop water coming in. Like gortex.

2. Economics: if you have a clay based earth in your area it's free, thus cheaper than cement.

3. Environment: Manufacturing a tonne of cement produces a tonne of carbon dioxide into our already choked atmosphere. Plus transport, distribution, sprawling factories, mountains carved up to extract the raw material. It burns your hands, stings your eyes, ruins your tools. Nightmare. Earth does none of these things and at the end of it's life an earth house can be turned back into garden.

4. Easy to work with: no need to pay specialist builders when you can do it with your mates and family.

5. Wood rot factor. We have found that any wood elements in our house that had been surrounded in cement plaster or external render was completely rotted. In contrast, where they had left the earth&lime plaster over wooden walls, the wood was still in perfect condition, after maybe a hundred years. I guess it is like putting your foot in a plastic bag to keep it dry, compared to a sock.

So last weekend Miriem asked if we would come and help with some earth plastering in her wee house in the Galician mountains we said "Sure". As discussed above, in theory it makes sense, now we need the experience. Either way, we like the idea of helping out with other natural building projects in this area. In fact there's a kind of network of folk between Galicia and North Portugal that get together fairly regularly to help each other out. So it was that Kira and I volunteered to represent our family, and off we went.

First off, we needed the material. Earth with a high clay content. It so happens that we've got loads of this right around our place in Troporiz, so Miriem, Frederic, Bugui and other Miriem came for some digging.



This is top spot (we found that day). No stones, high clay content (about 30%). Cool colour...

Quick cup of tea, with Madam Kiwi. Shared with Miriem and Frederico

Then onwards to Miriem's hill-top house, where the gathering of the Galician clans had begun.
Miriem decided she wanted an insulating plaster, to warm the place up a bit (or rather, to hold the warmth in a while longer). Earth plaster itself can be pretty straight forward: 30% clay, 70% sand and aggregates, water. Add straw to the mix and it beefs it up, giving it some insulative qualities. How much, I don't know. I suppose it depends on how thick you make your plastering. Adding straw makes it a cob mix (like Ken's house, or our pizza oven).


Miriem's house (on the right)

This kind of cob is usually made by piling straw together with the clay-rich earth and stamping on it, walking, squishing it together, to make sure the components are nicely mixed. As the snow was still fresh on the nearby hills, it was way to chilly to take off our boots and stomp around in a chilly mix. So in rolled the cement mixer, which we brought up from Troporiz.






The mix was more or less like this: 12 buckets of earth (about 35% clay content), 1 box of straw cut small, and 2 buckets of hydrated lime. Miriem decided to add the lime to help the plaster avoid build up of bacteria or fungi, which can happen in humid environments.

Straw cutting crew at work

Then we get it on the walls:) This we did in various ways, forming balls and hurling them at the walls, which they stick to wonderfully, or just applying it like you would any plaster.


Bugui (bearded) and César (with glasses) the leading Galician expert in straw bale and natural materials building, also seriously active with solar ovens, the Spanish strawbale network and permaculture projects.

Kira and Pedro (another Portuguese rep) soaking the stone walls in prep for the plaster.


Then Kira makes plaster lumps for Frederico...

























The final picture: 3 walls, first layer of plaster on. I think another "finishing coat", smoother, no added straw, might come next. Some rock left exposed on the edges. Not sure if these won't be like cold panels during the sub-zero winter months, but we'll have to see.

After work and much merry feasting, we decided we seriously needed a hot shower or bath, so we headed for the local thermal springs... (scalding secret spot well worth knowing about!)















A great day all round. Pilar, from Santiago de Compostela was inspired to pen this sonnet which sums it all up in far more eloquent ways than I can muster:

Corrido de los muros

(Ritmo: carabina 30 30)

Caminito a Covelo

Pa´cer el muro de Miriam

El arco iris ilumina

El corazón en la partida

Si un muro quieres revocar

Con los medios a tu alcance

Cal, barro y paja cortada

Constituyen buen aislante

Si arcilla buscas decantar

Y así saber su pureza

Con agua la has de mezclar

Que repose en la cubeta

1º Estribillo

Un gran arco iris en el cielo azul

Una hormigonera en la furgoneta

Un montón de manos y muchos amigos

Revocas el muro con menos pereza

Para darle consistencia

A la mezcla en cuestión

Busca mierda de caballo

Refuerza la solución

Mierda de vaca o caballo

De oveja no es suficiente

De cerdo no es solución

La nuestra no es eficiente

2º Estribillo

Si un nuevo mañana tu quieres construir

Una hormigonera en la furgoneta

Paja, cal y barro bien amasados

Y un montón de manos que apliquen la mezcla

Mucha gente agobiada

Por tremendas hipotecas

Así es como se lo montan

Pa comerte la cabeza

Un cobijo sostenible

Una vida sin dilemas

Mira oye qué estás a tiempo

De salirte del sistema

2º Estribillo

Si un nuevo mañana tu quieres construir

Una hormigonera en la furgoneta

Paja, cal y barro bien amasados

Y un montón de manos que apliquen la mezcla

Cuando trabajes en grupo

Revocando la pared

Recuerda la norma, compadre

Cerrar ojos y boca a la vez

Gafas son agradecidas

Guantes protegen también

Piensa que en boca cerrada

Ni moscas ni barro entran bien

2º Estribillo

Si un nuevo mañana tu quieres construir

Una hormigonera en la furgoneta

Paja, cal y barro bien amasados

Y un montón de manos que apliquen la mezcla

Tras un día de trabajo

Con la luna en creciente

El descanso es merecido

Termas y agua caliente

Pero maldada es la suerte

Que la terma está chapada

Mas recursos no nos faltan

Manos y una gran cizalla

3º Estribillo

Si un grandioso día tu quieres construir

Mete la cizalla en la furgoneta

Un montón de manos y muchas sonrisas

Rompen las cadenas con más firmeza

Qué cosas tiene la vida

Permacultura aplicada

Paja, barro y cal mezcladas

Luna y pelota picada

Ultimos estribillos y conclusión

Si un grandioso día tu quieres construir

Un nuevo mañana, una tarde, una noche

Un buen revoque, un muro, una casa

Mete todas estas cosas en el coche...

Un gran arco iris en los corazones

Las herramientas en la furgoneta

Un montón de manos y muchos amigos

Afrontas los muros con menos pereza