At the event Projecto Casa that will happen at Exponor, Porto from December 6th to the 9th 2012, it was made available to us a shipping container to present our work. We decided to use this icon for the global economy as the representation of the present model of economical growth responsible –in our view – for ecological and social unbalances. The adobe vault that we’ll build coming out of it represents a ecologically sustainable model of development to which we wish to contribute.
Here are two pictures that sum up our idea for the whole setup.
Earth is a remarkable building material.
It is used by humans for at least 9000 years. It has been the chosen solution for a wide range of situations, from small cabin housing up to the Great Wall of China and the Mayan pyramids in Mexico. As a proof of its features there are still earth buildings that, with more than 3000 years, are still standing. This construction technique is used in virtually all climatic zones on the planet and it is estimated that today, more than a third of the world population inhabits earth buildings.
Despite being one of the oldest materials, earth continues to be the subject of technical studies and innovations. Rigorous laboratory testing has provided us with an extensive and deep understanding of this material. Thus it is known that the earth has great benefits for the environmental comfort in buildings:
Earth controls inside humidity – because they exchange water vapor directly with the air, the earth walls promote constant moisture levels ideal for human health, preventing and reducing the incidence of respiratory diseases. By keeping these levels relatively low, these walls also prevent the formation of fungi;
Earth has a high thermal mass – this material has the ability to store and slowly release the sun’s heat, keeping the interior temperature constant and comfortable. This feature is ideal for climates with large temperature variation from day to night;
Earth filters out electromagnetic radiation – within an earth building the values of radiation produced by mobile phone antennas and power lines are negligible.
But what makes the earth really exceptional, even from a philosophical standpoint, is that it materializes values that make it democratic and appropriate:
Earth is a local material – (almost) all soils are likely to become a building material and since it can be obtained on the building site it avoids transportation’s high economical and energetic costs;
Earth has very little inbuilt energy – being used raw, the land prevents the use of heavy technology, as burning ovens, that consume a lot of energy and resources;
Earth is 100% recyclable and biodegradable – in all its techniques, earth can be reused without any limitation and to the extent that produces no waste or pollutants, it’s a truly ecological material.
Earth is low-cost – bacuse it can be abtained at virtually no cost, earth is an extremely inexpensive building material, especially when used in self-building;
Earth construction techniques are labor-intensive – this technique requires more manpower than building with cement or burnt brick but, when analyzed in conjunction with the previous (low cost), this feature turns out represent an opportunity for more equitable distribution of wealth, benefiting local population.
Earth is an appropriate material – for it’s versatility and simplicity, this technique allows any person or community to build, even without deep technical knowledge. All methods of earth construction are easily taught, and may be effective tools for self-construction in the service of individuals, groups and/or communities.
Built spaces are a crucial part of our lives. As it is organized today, construction requires the accumulation of material wealth to be carried out – for the purchase of building materials and to ensure skilled labor. Building with earth is inscribed in another order of priorities. Because it can be done by groups of non-specialists with simple tools and in sharing moments, construction of houses or any other building out of earth promotes the strengthening of link between people and the transmission of knowledge.
As a building material, land is compatible with values of solidarity and sharing tremendously important to counter the individualistic and competitive logic that dominates contemporary society that undermines both groups and individuals.
ep1 The Blades
ep2 The Alternator pt1
ep3 The Alternator pt2
ep4 The Frame
ep5 The End of a Beginig
Envited by the association Centro da Terra, a teacher from Sítio (Samuel Rodrigues) was in a Building with Adobe workshop at Faculdade de Ciências e Tecnologias da Universidade Nova (Almada, Portugal). The workshop (one in a 3 part education event – 1st Teoretical Approach, 2nd Rammed Earth and 3rd Adobes) add as an objective, not only the transmition of knowledge about the adobe production but, mainly, the construction of an adobe Nubian vault allowing for an even better understanding of the material’s possibilities.
Adobes, sun dried earth blocks, are one of the oldest building materials used by man – There are records of its use with at least 11 000 years.
These blocks are formed from earth (with the presence of clay) that is taken to a plastic state – by adding water – to which it’s normally added some kind of fibber (straw, horse or cow dung, wood chips, etc) that enhance its mechanical resistance. After formed – normally using small and simple wooden moulds – the adobes are sun dried. It’s an ecological and economical material that grants great quality to built environments.
Adobes have a good performance under compression stress but they don’t work under tension. Thus the vault we built has a catenary section. A catenary is a curve created by any chain suspended by its two extremes. The advantage of using this curve is that, when mirrored, it produces the optimal shape for a vault in whitch all structural forces are under compression and so, perfectly in tune with the adobes as a construction material. As a rule of thumb, the “theoretical” catenary curve should always be in the central third of the adobe walls and of the foundation.
An existing wall, built during the rammed workshop, was used as support for the chain, allowing to ajust the section’s dimensions in the building itself.
There are several techniques to build a vault most of them using formwork. In this particular case we built it using a method know as Nubian (for it was created in Nubia, a region located along the Nile in southern Egypt and northern Sudan ). This age-old technique has revived by the Egyptian architect Hassan Fathy in the 40’s. Its great advantage is that it renders useless the all wooden and/or metallic structures to be used as formwork allowing for cheaper and cleaner buildings. The method consists, basically, in laying the adobes on a certain angle so that structural stability is obtained even before the arches are closed and the mortar is dried.
We build a small formwork, plotting the line created by the chain onto a wooden sheet, that we only used for building the arch on one of the ends of the vault. We used it also to attach the strings that serve as visual guides during the construction work. This formwork could be avoided is we had a wall on each end.
Observations and lessons learned
This building was also a learning experience to Sítio. We managed to confirm and further comprehend some of the principles involved in building a Nubian vault:
1- The adobes must be light. We used 20x10x5 blocks with about 2 kilos. This allows that they don’t slide down while they are being supported only by the stickiness of the mortar avoiding the deformation of the section. Oftentimes square faced adobes are used to increase to adherence in relation to the weight.
2- The adobes must be laid forming an arch (or part of it, in the beginning) with an inclination between 60º and 70º. An angle superior to 70º increases the possibility that the adobes slide down as they are being laid or that the vault deforms. An angle inferior to 60º will produce sections with a bigger cantilevering mass before they start working under compression thus, again, increasing the possibility of deformation. We used wooden guides (triangles) with the desired angle.
3- Each (tilted) section of the vault should be finished before starting a new one. Starting new sections before the end of a previous one will also increase the cantilevering mass.
4- While laying the adobes you should minimize the amount of mortar in the interior face of the vault. On the external surface, specially when a lot of mortar is needed you can wedge a little stone between the adobes. These two precautions allow that even before the mortar dries the whole structure is working under compression avoiding, once more, deformation of the vault section.
Keeping the shape and symmetry
5- Even though building a Nubian vault doesn’t require a lot of accuracy to be completed, some small efforts can largely facilitate the work and assure a more precise shape, both visually and structurally. When laying the adobes on de sections of the of the vault you can create marks that allow for the for bases of the ongoing vault are built in symmetry.
6 – you should always keep a small (predefined) distance between the adobes and the visual guide lines. If they touch each other you can create an exponential error that can ultimately compromise the catenary section.
Click here to see photos of the whole building process.
Film produced by Timelessroom during the Agroforestry Workshop with Ernst Gotsch organized by Sítio in October 2011.
We’ve just published on this site the beginning of an interview with Ernst Gotsch on Agroforestry and his personal views. As will happen with other interviews we’ll make in the future, this one will be made over time by email allowing you- the reader – to participate in it. Just leave us your ideas for questions in the comments box. Thank you!
To read the interview…