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

Gathering wood to build our house

Donald at home, with his horse, self-built round house and in his woodland


We need chunky beams to build our roof, and others to hold up our floors. Joists I think they call them. Anyway, we need loads and we don't want to use concrete beams, covered in a concrete floor, which mystifies all our local builder friends: it's what everyone does. Why not, it's resistant, cheap, etc.

Where to begin? There are so many reasons why not: the environmental impact of the evil grey powder, horrible material to work with (wrecks your tools and your hands), doesn't perform well in terms of breathability: it's like wrapping your room in plastic so the vapours inside can't escape. Build your roof with it and you live in a plastic bag. Do we need any more reasons to choose wood?

Anyway, a wooden floor or roof beam can be exposed and look nice, maybe even curved a bit like the tree was. Maybe we can insert long bolts and swing from it. And so on.

So we meet Donald and Eleanor who live near Valença in their very own forest. Donald is a vet, and worked in his local community for 17 years or so. Now he looks after the ranch. Donald said we could take some oak trees from his place if we needed to build a roof.

So in August we decided it was time. August because we've heard so much about cutting trees at the right time considering the movement of sap in the tree. These are called the the "menguinte" and you are supposed to cut most trees only in the menguite de Agosto o Janeiro. It make sense: mid summer or mid-winter with be the stillest time for the sap.

The menguinte refers to the waning phase of the moon. As usual other things were happening and we got on to it a bit late, but we got started.

Within a week we had cut 17 of Donald and Eleanor's fine trees. It was quite hard to make the decision to end their eager lives, but Donald tells us that the roots remain full of energy and burst up through the stumps creating many new shoots. He cuts most of these, leaving say four, which grow quickly and in about 8 years are a good chunky size, useful for posts, fencing or firewood. Oak coppicing in other words.

Meanwhile, everywhere we looked we saw baby oak trees growing in every possible space. This is a truly native species and seems to grow at a tremendous speed. The biggest trees we cut were only 25 years old (counting the rings). In Scotland, a tree this size would sure take twice that long!

We arrived in teams. At first myself and Paulo. Then we picked up Shawn for the bread oven and he joined in. Heather and Sophia joined us the next day as we realised how much work clearing the branches and brash was taking. A few days later we increased the pace bringing out our heavy artillery: Machado (local everything worker), Nikita, Logan and Cyreeta and Mary.

After this onslaught we had whole trees strew across the land. Firewood and brash piles rose in newly illuminates glades. Our desired length for most joists was 6m.
This meant leaving extremely heavy chunks of tree lying around in mostly hard to access bit of woodland. How were we going to move it all?


Machado said we needed a "tractor do monte" (a mountain tractor). We called Pedro and he brought his quite amazing hill moving machine.

Fitted with two massive winches, he puts this scary looking tractor in a strategic position, pulls out chains and ties them around the base of trunks. Then stands back and lets the machine do the work: on remote control! Yes, as if by magic half a dozen of these enormous trees move obediently towards this vision of future mooon-scaping. Mary, Donald, Eleanor and I stood like fascinated villagers who had seen a car for the first time. We got lifts in the wagon and played God with the remote. Within a few hours we'd shifted around 20 tonnes of oak to the road side.


Next day, Pedro brings his techno-truck. Awed by the tractor, we were blown by "The Claw". This is a mechanical arm controlled from a precarious looking cockpit above the back of the truck. It moved with the speed and accuracy of your arm. It had the delicacy too: it could pick up small branches and gently relocate them. Or grab whole car-size lumps of earth that were in the wrong place and lob them, like a gormless cricketer, into the beyond.

Once again, we googled open-mouthed. I wondered how I can have missed all this technology development. I suppose I don't work around modern technology in forestry. My only experience with moving wood was in Romania, where we did it all by horse and cart. Seemed to work pretty well too, and would have done here. But moving all the wood the 20 odd miles to the sawmill would have taken forever by cart. Anyway, this is the space age, and we borrowed kit from the Mars programme and enjoyed the show.

Senhor Jorge, at the sawmill was a bit dismissive, saying most of was "lenha" (firewood). He is used to working with massive trees as wide as his own barrel-like girth. He says the heart wood is the only usuable bit, the white outer wood is vulnerable to rotting, bugs and so on. Wish someone had told us this before. We had been hoping he could cut one edge of it for us, leaving the rest in the round (as floor joists would rest of these beams). I'm still sure he can get a few rafters or joists out if it all, if not major beams. And there's plenty of posts for building sheds and the like (chicken coups come to mind).