SHIBAM
STUDY ON RAMMED EARTH Marie Magnien - Technical Studies
INTRODUCTION Last year, in first year of architecture in Marseille, I had a lecture about Martin Rauch and his rammed earth house. It was about how he built his own house with the earth he extracted from the land it is built on. I found the idea absolutely incredible. I did not look much into it, but this year when we had to find a subject we would like to study, I remembered it was something I would be thrilled to know more about. Rammed earth has been used by all kind of different civilizations, for centuries. You can find an example on almost all continents. Mainly used for housing, it is a material you don’t need advanced knowledge to work with. You don’t need impressive machinery too. It is an incredible material that sometimes challenges science (The buildings in the city of Shibam or the Great Wall of China, the only human-made structure that can be seen from the moon !) And the best part about it is that it can be 100 % natural. No need to use chemicals, as for concrete, to create a rammed earth structure. At first glance it seems like anyone could create anything out of it. But is it really that simple? This semestre I will try to create my own piece of wall, without using any chemicals. Only earth I would find somewhere close to me. Despite being really ancient, rammed earth is for me an incredibly futuristic material. I am glad to see it is back into fashion and that more and more contemporary buildings are made entirely or partly out of rammed earth. I want to look at the weakness of the material. How difficult it is to create an opening inside a rammed earth wall? Are all the different kinds of soils good for this type of construction? Can I really go out and collect earth from my garden and make a wall out of it? I hope I will be able to build a strong and good looking structure that will demonstrate the power of this amazing material. We simply need more rammed earth in our life...
Martin Rauch House When in first year architecture degree in Marseille, we were taught about Martin Rauch and how he made his own house out of rammed earth. I have been really fascinated about this process. When we had to choose a subject to study this semester in “technical studies� I remembered this house and I thought it will be something I will be particularly interested in investigating further
Martin Rauch Video
“Eco builder”
Martin rauch has developped the notion of controlled erosion of earth constructions. It is certain and inevitable that all materials will deteriorate. Only the speed of the process changes. Earth constructions are well-known for their many qualities (cost, universal availability of material, good thermal performance, etc.) but they are affected by a major drawback. They are very susceptible to erosion. All training courses in earth construction first recommend their protection with “good boots and a Rauch house, detail.
good hat”. Putting these instructions into practice drastically reduces the possibilities of architectural expression, and has slowed the development of earth construction martin Rauch has a different approach. The goal is not to prevent erosion by a method exterior to the rammed earth wall, but to find under what conditions this wall can be protected by its own properties and by materials it is made of. A rammed earth wall has a clay and stone surface. The first rains will carry the finest particles with them and a certain number of the small surface stones. They will then show a “second front”; a new surface made of embedded stones, stabilising each other, and which at their scale are arranged in the manner of a stone wall. structure of the This new surface rainwater runoff This is adjusted
The particule size must be controlled, so that the granular wall is as compact as possible. will be stable and sustainable as long as the speed is not too high. by regularly laid foundations (terra cotta slips).
Visit to the ecology centre at Holland Park
LET’S GET STARTED After my primary research and my visit to Holland Park I decided to stop and get started, I had enough information to try to create something. Rammed earth is a raw material so it needs to be manipulated in order to be understood. First I needed a mold, a formwork, to pour my earth inside. I did not want to make a too big piece of earth, it would be too complicated to carry around. After some research drawings I decided to go to the workshop at Westminster and make the mold with wooden boards.
Formwork
At that point I had no idea of how much earth I would need for a, let’s say, 20 x 43 x 15 square of rammed earth. I decided that one big supermarket bag will be enough... And I went to my local park to collect some soil.
Soil
It had been raining for days when I went to collect the soil and all I could get was mud. I tried to test it anyway, even if I knew up front it would not be the perfect conditions. I thought the earth would just take longer to dry but maybe, it will be easier to stick all the layers together because of humidity. So maybe it was still a good idea to test really wet earth to compare with dry one.
Roundwood Park, NW10
EXPERIMENT 1 I was using a ladle to take a small amount of earth from the plastic bag and put it inside the formwork. As you can see on the picture the earth is extremely wet. Because it is very compact it can’t be sifted. There were still pieces of plants and other microorganisms mixed with the soil.
Layer by layer I had to ram the soil. My approximation of earth needed to fill the formwork was not correct. Because it is tammed really tight you need a lot just to create a small layer. At the end I was able to fill less than half of the framework.
Formwork without earth. You can see that soil left marks on the side. I also had to circle the mold with wire because it was not tight enough
Here is the final piece of earth wall. Because of humidity it is not flat and not rammed properly. It is not smooth over the top. It is only 7cm tall because of the lack of soil.
When I finished the last layer I needed to remove the formwork for the earth to dry. The soil was highly adhesive. I used a knife to unstick it from the sides.
I leave it to dry and after 7 days it was still wet, I could make holes on the top with my fingers.
EXPERIMENT 1 - Conclusion
After 3 weeks EVEN AFTER WEEKS OUT OF THE FORMWORK THE PIECE OF EARTH WAS STILL NOT ABLE TO DRY COMPLETELY.
It looked like a wizened skin, with big cracks in the middle. The most impressive was that there were molds and mushrooms growing on top of it ! What I learnt from Experiment 1 :
- The earth needs to be extremely dry, almost like sand, but with still a small quantity of clay, otherwise it can’t stick to- gether. It would be easier to add water to a dry mix than working with wet soil from the start. - I need earth in big quantity, a supermarket bag is not good enough. - I need to build a very strong formwork otherwise the earth won’t take a square shape. - I need to remove ALL grass and microorganisms from the earth otherwise they will continue growing and will damage the construction.
EXPERIMENT 2 - TALLER AND WITH AN OPENING 1 - thinking about the size of the formwork and preparing the boards to be cut with a circular saw. 2 - Cutting different pieces 3 - Put together the formwork 4 - The formwork needs to be strong. I strenghten it on the corners with nails. The formwork is fixed to a base with nails. (red cirlces on picture)
3 1
2
4
SOIL PREPARATION This new experiment is made in Marseille, France. In London it was really difficult to find good quality earth. It was way too wet. In Marseille I took soil from my garden and I mixed it with sand. I added water, as much as needed. I got a perfect mix for the rammed earth construction. A good point is also that I had unlimited ressources. In London, I realised I needed more earth than I had to finish and fill completely the formwork.
CREATING A WINDOW
UNMOLDING & FIRST ISSUE I removed the mold as soon as I finished filling it. For the first minutes it was fine but as soon as the piece started to dry it collapsed on the sides. As seen on montage A, I did not put sands layers all the way up to see if it will make a difference... And it made one ! The soil was too wet on top and collapsed as soon as the mold was off. Because there is a window, you need the top to be really dry, strong, so it can stand side pressure.
The top part is collapsing. It is too wet and can’t stay still. It needs to be stronger, especially because it is the part that is holding the window frame.
At the bottom part there is a soil layer / sand layer interval. We can clearly see it is stronger and dries quicker.
A
This issue was a good way to understand better how rammed earth works. I removed all the part without sand layers and I just made the piece again. Humidity is maybe the most important fact. A wet piece is not going to dry and if it is not drying quickly enough it will collapse. I removed the mold and this time it stayed still better. Of course it is not perfectly straight because of the window. I understand that to make a flawless piece you need machines to ram the earth. The layers need to be extremely tight.
EXPERIMENT 2 - Conclusion
After 1 week I left for one week for Christmas and when I went back the piece dried completely BUT it had a huge crack on the left side of the window. It was strong but not very aesthetic... What I learnt from Experiment 2 : - Mixing soil with sand is good but it’s not enough you also need to put sand layers in between soil layers. - Creating an opening is really complicated. It really pushes the sides of the piece. I think the window should be created differently. As seen at Holland Park’s ecocentre, they made all the walls first and then filled the gaps between them with wooden boards. - I think removing the formwork as soon as you finish layering is not a good idea. It is better to leave it for a moment, the piece dries way better and keeps a square shape. Especially if you have a window, the sides will collapse more ea- sily. - When the piece dries it cracks. This is a sign of a maybe too wet earth at the beginning. It may be good to cover it with something to protect it, such as lime.
FINAL PIECE - JARDINIERE After building a piece of wall with window, I planned to build a jardiniere, 30 cm long, 24 cm wide, 21 cm tall and 8 cm thick.
The earth was taken from the garden, rich in clay. I used a grid to remove all the stones. Then, it was mixed with sand (10%) and humidified to be more easily compacted. Wetting of the soil was tricky. too much water and earth cracks when drying, not enough, it is difficult to compact and is too crumbly, as I have observed during the construction of the wall with window. The boards are made out of plywood and cut with a circular saw. The jardiniere is placed on a board. Then I hammer nails to wedge the bottom of the formwork as we could do in reality, in the ground. Same technique to create the inside box. At the top of the formwork, I connect two by two the boards with cardboard (wood would be used in reality). With a mason’s level, I check the verticality of the formwork and I nail the cardboard to the boards. I can now start to fill the formwork with earth.
LIME PLASTER
After drying the whole day inside the formwork, I planned to cover the jardiniere of a lime plaster. In 100 g of water, I mixed 25 g of slaked lime to obtain a milk of lime I spread with a brush on the still wet walls. I waited 24 hours between the first and the second layer.
CONCLUSION I am glad I undertook this study on rammed earth. First I am really pleased with the final outcome. After numerous attemps I got a beautiful and strong piece of wall, Without machinery or complicated tools. It was interesting learning more about this unknown material. It can actually be used to build a wall, or something smaller, like a jardiniere. It is particularly attractive when you know I have not used any chemicals to make these pieces of rammed earth. With the lime plaster it can be protected against weather elements. In the future, it will be all about sustainability and inovations. As an architect, I think having knowledge of rammed earth construction will certainly be useful.