Week 8 – Eco-building in the Pyrenees, from earth bag foundations to plastering
Posted on 20 July 2011
This post will actually cover the progression of Pierre’s projects in the Pyrenees over a 2 week period as we would like to use the last post, week 9, to share Pierre’s experiences of hosting volunteers for his projects.
During my last 2 weeks at Pierre’s, we completed the ceiling insulation (see our week 5 post for details), continued painting the window frames (inside and out), finished plastering the internal walls, plastered the first coat for an external wall, made some earth bags, finished sanding and painting the floors, added some creative elements and contributed to some gardening in preparation for Anne and the family to move in.
We had some extra helpers arrive, Ann and Hannah, who added some great energy to the group. Jean also arrived in time to spend a week helping out after being awarded his doctorate! I’m so proud of him!
Earth Bag Foundations
Pierre kept the earth that had been excavated from the site for the house for filling bags and tyres for his foundations (see the picture to the left of the excavated soil being loosened). We didn’t get a chance to make any rammed tyres but we did make around 53 earth bags.
For your information, rammed tyres are car tyres which are rammed full of slightly damp earth using a sledgehammer. Apparently the average car tyre will absorb around 136 kg of earth. They are then laid out like bricks. According to the book ‘The Hand-Sculpted House’, rammed tyres are stable, durable and thought to have excellent seismic resistance because they can bounce around a bit in an earthquakes but return to their position. The book explains the disadvantages though which are: they are extremely labour intensive to fill (a strong person can fill one tyre in perhaps an hour of constant ramming), tyres are very wide which makes them difficult to design around, their size and shape limit how you control the form of the building, it can be difficult to get clay based materials to stick to rubber… not to mention the health effects of possible off gassing from rubber tyres…
The earth bags, however, have most of the advantages of rammed tyres with fewer problems. Many sorts of bags can be reused for this purpose – natural fibre coffee sacks to woven polypropylene feed sacks (which is what Pierre uses). However, the natural fibre bags will decay when exposed to water while the polypropylene bags will break down rapidly in ultraviolet light. Protecting the polypropylene bags with a mud ‘sunscreen’ immediately after construction and then covering them with earth or lime plaster can prevent them breaking down… or in the mean time, as Pierre does, cover them with strong black plastic. (Note: polypropylene is a relatively ‘clean’ plastic that degrades into benign components.)
According to ‘The Hand-Sculpted House’ the bags can be filled with anything from sand and gravel to heavy clay soil which makes it a versatile and inexpensive technique so this is a perfect technique to use up Pierre’s excavated soil!
The bags should be filled with slightly moist earth and the ends sewn closed. The book recommends using nails or simply placing them end to end against each other to prevent them from opening, but Pierre prefers to sew them with wire as shown in the below pictures. From the first picture to the last, here are the steps: Fill bag with earth, fold over top of bag, punch holes through the bag and sew with wire, tying the ends off. With a small group of people the tasks can be broken up and the experience enjoyed together 🙂
We concentrated on filling and sewing the earth bags, but normally, once created, the earth bags should be compressed by stomping or with a heavy object. Pierre places continuous strands of barbed wire between each layer of earth bags to prevent the bags from slipping and provide tensile reinforcement through the whole foundation – also providing additional earthquake resistance.
From what I have read, the main disadvantage of earth bags is the possibility of moisture getting through the bag and causing the clay soil inside to expand and heave or through capillary action moving up in to the wall of the building. Pierre has ensured good drainage with gravel and rammed tyres underneath them.
Plastering an external wall of the house was a great group activity! Pierre chose to use a lime-sand plaster as this wall would be the one affected most by bad weather so would need to be durable.
Here is some information from my research about lime. Lime is made from calcareous rock such as limestone or chalk that is heated in a kiln to about 900 degrees Celcius, turning the calcium carbonate into calcium oxide (or quicklime). It is then slaked by mixing it with water which is a hazardous procedure that releases instant heat, boiling the water and splashing out caustic lime. You then have lime putty which is calcium dihydroxide. After soaking it in water for a minimum of 6 weeks it can be used for making plaster, lime washes or mortars… or dried and sold as bagged, hydrated lime. This must be soaked in water and turned back into lime putty before it can be used. Then, once plastered on a building, left to dry and exposed to the carbon dioxide in air it very slowly (over 3 years) turns back into calcium carbonate, effectively coating the building in a thin limestone skin! This is fascinating to me! In case that all got a bit too complex, here is a diagram of the process I found online which is similar to the one I’ve been looking at in ‘The Hand-Sculpted House’:
If you are going to use lime, note that bagged lime sold as type S or N builder’s lime has apparently noticeably less strength than ready-made lime putty or quicklime slaked yourself. However, this is the most easily available option and is a better choice than cement!
- 1 bucket sieved earth
- 2 buckets sand
- 1 bucket lime
- ½ bucket flax fibre
The flax fibre is added to prevent cracking. From what I have read you could also add chopped animal hair, hemp fibre or chopped straw but there are also reports that lime’s causticity destroys cellulose… so make your own mind up about that one!
The process of applying the plaster involves wetting the wall with a brush and then flicking lime water (a very runny solution of the plaster) to improve adhesion of the plaster. The plaster is then applied using trowels. The lime plaster needs to dry slowly so the surfaces need to be protected from direct sun and drying wind during and after plastering. Following are some photographs from the plastering and mixing process.
Sieving the earth, using an old bed spring:
Mixing the plaster, following the above recipe:
Flicking the wall with lime water can be a messy process:
Getting Creative – Sculptures
Ann and Hannah made a stunning contribution to the house by creating a tree sculpture with owls sitting on the branches to represent Pierre and Anne.
Samantha also contributed a beautiful creative element to an internal wall of two birds. This was the perfect way to end the hard work she put in to the internal plastering of the walls which she made a huge contribution to! I’m sorry this photo isn’t clearer…
You may remember from our week 6 post that we had some discussions with Pierre about elements of architecture. Part of this covers how Pierre uses colours and body of light to paint within a space. Below you can see how Pierre has painted the ceiling of the mezzanine floor white to reflect light in to the darker lower level.
In the following photos you can see how the outline of the body of light has been painted on to the wall at different moments in time. This can give inhabitants a feeling of time (without a clock) as they notice the light changing against the outlines throughout the day.
Pierre also started painting some of the walls using clay-dung paint. Using natural clay like the pink coloured clay, pictured below, and mixing it with cow dung makes a beautiful earthy coloured paint that still allows the walls to breathe. Pierre simply looks for coloured clay locally.
We didn’t just contribute to the building while we stayed with Pierre. There is also work maintaining the site and gardens. Jean spent some time cutting grass and weeds back and helped me build these garden beds for Anne’s lavender. Hopefully the cardboard, straw and timber borders will help keep the weeds at bay.
It’s not all work…
There’s also a lot of play…
Some of us joined a group for a meditation session using the OM sound which was very enjoyable… We joined in Anne’s music group for a bit of drumming at a local market…
We sang enthusiastically to music whilst plastering… and even felt energetic enough to dance a bit too! I will really treasure the time I spent with Pierre and hope to come back to visit and learn more again one day…