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As we have seen, the mockup or test vault is an excellent tool to train masons and to give the confidence of working with the thin-tile construction technique. But even at this scale, the risk of collapse is evident. The structure must be designed for stability in all phases of construction, and further the proper sequence of construction must be followed for a vault to be stable. Since certain states in the construction sequence are less secure than others, if laborers don’t understand how vaults work, the vault may be loaded in an inappropriate way, causing a collapse to occur which can injure workers.
Thus, the lesson plan for laborers cannot merely be an exercise in the technique of thin-tile masonry construction, but must rather emphasize “skills, structures and safety”, synthesizing construction technique, applied structural principles and concerns of safety. Builders must be familiarized with structural principles and offered tutorials about compressive load paths, so that they begin to get a feel for what makes a vault stand up. They must learn to always work with load paths in the masonry, insuring that any loading of the vault is sufficiently transferred to the supports. Such critical aspects of the behavior of masonry vaults must be taught to laborers for them to understand safe practices on site, e.g. how one may or may not load the vault during construction. For instance, if the scaffolding is entirely under the vault, forcing workers to work directly below the vaulted surface, they are not only more at risk should a collapse occur, but may also precipitate a collapse by accidentally pushing up on the vault from below (inducing tension into a compression-only structure).
Yet, if there is no shared language with laborers, how can they understand lessons for a new construction technique, let alone comprehend applied structural principles and the associated safety implications? Such critical concerns may at times be a tremendous challenge to communicate, but may nevertheless be taught in a very straightforward manner, when demonstration materials (like chains, buckets, etc.) and direct feedback (like loading tests, controlled collapses, etc.) are combined. In Ethiopia, where – again – material is very much constrained, one must be resourceful with teaching tools and modify the tool of choice (or method of instruction) based upon the understanding of the group. One must pay close attention to distinguish when an important point has or has not been understood.
Drawing becomes a very important tool in this context; even the crudest of drawings scratched into the ground, soil masonry surfaces, or drawn on hands are tenfold more descriptive than words.
When language is not shared, a great deal of patience and also a dose of the absurd is sometimes called for to make understanding possible, while alleviating the stress of not understanding experienced on both sides. Language can itself be employed as a learning tool, used in a gaming manner to play on double-meanings or the sound of known words to make a meaning known. When teaching with incomprehensible words… if you can’t make someone laugh, you are in trouble.
The first efforts at the full scale must be carefully observed, anticipating the behavior which compromises either safety of crew or safety of the structure. Ultimately, a balance must be struck between directing, working with laborers, and giving workers space to learn from error and figure it out themselves.
The goal, however, is to transition a crew to teaching each other as rapidly as possible, to reduce teaching interventions (and these only in the case in which safety is compromised). If laborers can effectively train and correct each other, than it is automatically much easier for them to correct themselves. Because the knowledge and transmission of skill is very much language-based, careful hierarchies of training should be established ‘on the ground’. A well organized training schedule can develop into a robust information transfer system.
Once the first phase of training has been accomplished, the training may become more complex. The timing between a mixer and brick layer must be well coordinated with this rapid technique – plaster sets very quickly and must be well-timed to minimize error and reduce waste. Developing a proficiency with the technique and building at an efficient speed are a difficult balance to strike, and one must alternately train the skills of accuracy, speed, and waste minimization to be used at the proper times. Techniques may be introduced to build speed, for instance, yet laborers must identify the critical areas which require reduced speed and accuracy.
Training laborers to auto-correct – or see their own tendencies to error – also means teaching them to be aware of sight-lines, their perception of accuracy based on their position on the scaffolding, and training them to change their position to better identify certain errors. They must learn to recognize the difference between an acceptable/ negligible error and one which has structural consequences; they must learn when it is necessary to remove masonry in order to most efficiently correct a problem and also learn the techniques of knocking bricks off a cantilevering surface without causing a large collapse.
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This will be a short post, since it must only be said that trust must exist for a crew listen and work with care. As I have seen far too often, a crew which has neither respect nor trust of its supervision has no accountability for the quality of work it produces. When language is barrier – as here in Addis, where 2 of my crew out of 30 spoke a working level of English – this is even more so critical.
Imagine for a moment, a short, blonde, white woman giving orders on a construction site in Africa. Respect for leadership only occurs when there is a clear respect for the laborer – which means being willing to drop the camera and to share the hard work with your crew, to earn it.
Photo by C. Lippuner
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I wasn’t just training laborers, however, but teaching students as a part of the ETHiopia Urban Laboratory Summer School, hosted by the EiABC and run in conjunction with the ETH Department of Architecture, ETH Sustainability, ETH North-South Centre and the BLOCK Research Group. The participants of the summer school were ETH and EiABC students of architecture, entrepreneurship, and water and sanitation, as well as representatives of local construction cooperatives.
I should hope that the juxtaposition of the phrases “training laborers” and “teaching students” raises some red flags here; indeed, the inversion of these teaching modes is a relevant topic in the context of capacity building in Ethiopia, and probably one of the more invisible aspects of the success of the workshop. The students had one week of lectures, followed by two weeks of the practical component of the workshop – enabling a translation from theory to praxis. Rather than merely “training laborers” and “teaching students”, we were also training students as laborers and teaching laborers as students.
As a part of this program, we set up test vaults on the ground for students to experiment with the techniques of tile vault construction. The foundations built for the test vaults established three types of boundary conditions, the purpose of which was to facilitate practical experience in the constructional and structural principles of each vault typology:
1. A Single-curved barrel vault (similar in basic geometry to the full scale SUDU)
2. A Double-curved barrel vault
3. And a Double-curved vault, springing from edge arches
The group’s exploration of catenary structural principles was evident in the development of their guide-work strategies – perhaps ‘easy’ when any material is available, but quite challenging when one has no reliable lumber or cutting tools.
For the students of architecture, there was of course a different goal employed in the teaching strategy, beyond that which overlayed construction method and structural system. Just as in the full scale construction, the materials, the tools and the available skill-sets were limited. The students were asked to engage in a process of design unique to these circumstances, designing everything past the boundary conditions with only the few tools available to them: A chain, some mixing tools, and some scrap wood from broken-down furniture. Guidance was provided with respect to material techniques, formwork strategies, structural behavior, and tiling logics to keep the vaults stable during construction – but mistakes which produce collapses are, more often than not, more valuable learning experiences than instruction. The constructional solutions developed by the students were manifold and demonstrated an extremely creative use of ‘nothing’, among them: the use of nails in recycled boards to set the first masonry arches in cantilever, materials such as telephone wire for string, sliced bamboo for formwork, strips of eucalypis peeled from neighboring trees to describe curved masonry surfaces.
Material resourcefulness and frugal use of material went together. Danny, one architecture student at the EiABC, noted that while others’ had criticized his craftsmanship, the tiling pattern he developed nevertheless greatly reduced the use of the most expensive construction material, gypsum.
All the while, this Summer School occurred – rather uniquely – in the context of a the construction of our full scale vaulted SUDU prototype, spanning approximately 5 meters with a 7 meter length. So, as the students pursued their own problem-solving on the ground, the project managers and laborers engaged in some of our own at the full-scale laboratory study. While the first cautious steps were taking in loading vaults with varying heights of less than one meter, great care was demanded in the construction and loading of the full scale vault.
The test vault serves a critical function both for students and for laborers, allowing for the development of skills in a safe and controlled manor, while serving as an analogue to the full scale structure. They are an effective tool for the development of knowledge in applied structural principles – clarifying critical topics such as the outward thrust of a vault, the function of tension ties, the benefits of stabilizing ribs, etc. A collapse teaches the boundaries of structural stability during construction – yet without such training in the structural behavior of masonry vaulting, constructions at full scale may take unnecessary risks.
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The context for the construction of the SUDU – according to scientific director of the EiABC, Dirk Hebel – is an “international research laboratory” for the development of this low-cost, sustainable housing prototype. But what constitutes the aims and the challenges of an International Research Laboratory? The outcomes are as much embedded with concerns of the technical as they are with the cultural.
One may recognize this phenomenon in the simple terms of critical materials acquisition: The thin-tile or timbrel vault construction technique relies on the use of a rapid-setting plaster-of-paris (or gypsum) mortar, which allows the first course of masonry to be set in cantilever from the masonry surface without the support of formwork from below.
Photo by C.Lippuner
If a cement mortar, for instance, were used for such purposes, the mason would have to stand in one place on the scaffolding for several days to support the brick while the mortar dried. This is perhaps an absurd picture, which nevertheless conveys the importance of plaster mortar in this technique: because the mortar cures so fast, no formwork is required from below. Nevertheless, if a team of masons could only mix the mortar for one brick at a time, it would take months to built a vaulted structure. The efficiency of the method lies in its rapid-setting properties, which may be strung in small batches to maximize efficiency in the work of the masons. Thus, the properties most ideal for the raw plaster material is that it sets rapidly, while remaining workable as long as possible to set many bricks in one batch.
In most places of the world, plaster is very a common construction material – indeed, plaster is also produced in Ethiopia. The properties of acquired materials, however – very much like cement – are simply not reliable without engaging the levels of both technical and cultural investigation. With all industries, in the West as in the developing world context, there are manufacturers with reasonably trustworthy products and manufacturers of the lower order where one cannot rely on material properties. The best respected of plaster manufactures in Addis Ababa is a company called “Sede”. However, the constraints of production, and the competition in the market significantly complicate the acquisition of this material. If one goes to Merkato (the largest market in Africa, based in Addis Ababa), and one purchases plaster in packages labelled “SEDE”, one is sure to have acquired a knock-off using the name of Sede to sell its product. This is common knowledge to the local who works in construction. Sede, though producing the best plaster, does not produce paper bags for its packages. It may use plain brown paper packages, but it often – as in our case – uses the packages of the plaster manufacturer “Mughal”. In this respect, it is quite impossible to find the material one is actually specifying in Addis Ababa, unless one is to investigate more fully.
Plaster is most produced in Ethiopia for wall plastering, the dominant use in many other regions of the world. Yet the working qualities for wall plastering is indeed quite different from the qualities required for timbrel vaulting. The former, for instance, is often combined with fine sand and is optimized by both manufacturing and working technique to dry very slowly. Since the properties of this material are so critical for our purposes – and since the first tests failed to adhere even one brick with such low-order, sand-doctored plaster as acquired in the markets – we invited a representative of Sede to the construction, so that he could observe our method of working and thus more fully understand our required working properties. With tall graduated glass cylinders from the laboratory, the plaster was mixed to demonstrate the poor results. I then mixed the plaster brought from Sede, certainly a pure plaster, and the results were better, though not entirely uplifting. It would take a long time to train inexperienced masons which such a finicky material. The Sede employee then demonstrated the techniques recommended for their typical wall application, which seems to have the exact opposite effect as desired, setting was very slow but drying was very fast, meaning that the plaster rapidly lost its plasticity, while still taking a very long time to fully set. With these experiments in mind, and with a better understanding of his part on how we needed the material to perform, we discussed possible manufacturing techniques which would allow the material to set more rapidly and remain plastic. I suggested that the material be burned longer, or alternately at a higher temperature. He concurred that the company’s techniques to produce the best slow-setting plaster could be reversed to produce more rapid-setting qualities. It should be dually noted here, that the Sede representative spoke no English, and I spoke no Amharic, though we fortunately had some reliable translation.
And, with the days counting down in our limited period for construction – it was a tremendous relief that this little experiment worked. One material sourcing crisis was averted, but the implications of future construction is clearly enough demonstrated. The research that must be done to implement this technique at a larger scale – well, it must be pursued also across cultural lines.
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Confronted with the restrictions of minimal financing and insufficient material – or no money, no material, and no time – it is clear that the repercussions do not simply impact construction methodology, but indeed the culture of design itself. In Ethiopia, ‘design’ itself becomes problematized, challenged by a necessary mode of improvisation, through which the complicated chain of resource constraints is negotiated. Upon more careful inspection of this Ethiopian culture of design, one recognizes not only improvisation, but the complex social nature of this improvisation. On the scaffolding, this makes itself evident in highly complex physical manoeuvers requiring the participation of more than one person. It might be said that the typical Ethiopian has a radically different sense of spatio-perception, based perhaps, on the average population density and their socio-economic inter-dependency. This problem-solving functions as a form of cultural development, a form of collaboration rooted in socio-economic inter-dependency.
As an aside, I have been told that it is common practice for a poor family to share one day’s excess of food with a community, rather than saving it for the family unit for later. Indeed, a Westerner would typically recoil if his neighbor were to reach over his should at the dinner table, take food from the plate with his hand and share in his neighbor’s meal. But this mutual recognition of interposed space-boundaries would seem to be a broadly cultural phenomena. Bodies and their space boundaries overlap in humorous and surprising ways, enabling uncannily many tasks which could not be achieved by one person.
To contextualize such abstracted speculation, let us examine the first stage of construction of the SUDU vault:
The first set of drawings for the guide-work for the SUDU vault were produced in the office – in principle, a simple, light-weight wooden truss structure to accurately describe the geometry at the terminal edges of the funicular barrel vault. Again, because the timbrel vaulting technique employs plaster on the first layer of masonry and the masonry units are consequently applied in cantilever until each arch is closed, only a non-structural guide-work is required to accurately describe the geometry for the masons at the end wall of the structure. Between the two guides on each end, string is pulled taught to describe the surface.
However, here, the design process is shaped by a totally difference set of constraints, such as the availability and cost of milled lumber. Material availability – cost of material – skilled labor set availability. These are very significant factors of constraint in construction, which – in the West, particularly in academic design – very often come after architectural idea and design development. The hermetic office-design on paper, which cannot modify itself within external constraints in the field, is most often the project that fails to meet the criteria of local economic and environmental sustainability; and in Ethiopia, which more often than not cannot be built outside of the context of high-end corporate architecture. The small but growing corporate constituency of Addis Ababa evidently favors the international symbolic influence of concrete frames, steel and glass facades. Our goal however is not to build unsustainably for corporations; but to develop low-cost housing for an exploding population, the resources for which are extremely limited.
Design moved next to the workshop – where we met with our builders. The workshop was a ragged tangle of cheap stock and old tools – with a wood-shop on one side and a metal fabrication shop on the other. Then we sat down with wood and metal workers to discuss our options – our design table consisting of a stack of lumber on the floor.
When I observed and participated in this highly social exchange, I realized for the first time this profound difference in design methodology in Ethiopia. It can’t be properly described, but it was as though the debate that ensued through language was only a linguistic or intellectual equivalent to the balancing of two laborers on a thin eucalyptis beam, 7 meters above the ground. The act of debate was – with sensitivity and directness – both linguistically and physically socially mutualistic. The answer:
Was to fabricate the guide-work for our vault in welded steel – with angle and flat stock readily available, relatively cheap, with the presence of skill necessary to accurately describe the material for our catenary surface, and the efficiency of labor in the rapid time of fabrication possible through this method. An intelligent solution, which no doubt saved us time, material and money.
The transition from design space to construction was eased by the full scale catenary templating, which we had brought along to the shop (see header image). Since there had been a long role of paper cheaply and readily available, we had traced the catenary geometry – established by a chain between the points of springing on two opposite surfaces of the ring beam – directly onto paper. With boundary condition geometry thus established, the depth of the vault per our calculations only had be controlled by the length of the chain. This full scale template of our vault curvature was rolled out on the metal shop floor, at which point the fabrication debate with steel over paper continued almost without difference from the design debate with pen over paper.
From design paper to construction paper, the development of the construction document was entirely by-passed. Established plans – such as what stock pieces to use, where to position them, how to treat the joint – were modified in real-time by the feedback of an empirical process. It occurred to me, with some irony, that our workshop crew worked as effectively and efficiently on the shop floor as a well-trained architect in a CAD space. And strangely, with similarity of method. I had to note my own long-held complex between the terrains of architectural design and constructional practice, and acknowledge that here, that discrete boundary did not exist as I have known it.
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The first principle of building in the context of a resource-constrained country such as Ethiopia is to accept the reality of resource-constraints – including raw material, tools, infrastructure, power, and even shared language – and to understand what advantage it confers. Perhaps this is an obvious observation, but I have noticed that this is one of the greatest failed opportunities of Western support mentalities in Ethiopia.
For a little context, imagine some of these everyday scenes from the street. Some minor acts of resourcefulness seem to make sense to the foreigner, whereas others leave one wondering – how could such an absurd thing come to pass?
Photo by C. Lippuner
When we paint the picture a little more vividly on the construction site, however, one begins to understand the story that accompanies each creative solution to resource constraint:
One of the few power tools absolutely integral to this construction is a 2000 BIRR hand grinder, used to cut all of the edge and arch-closing bricks for the vault structure. In the event of the [generally daily] loss of power, the crew must improvise to cut as much as possible during the window of power, without burning out the motor from over-use. When the grinder is broken, it is necessary to fix it, a tradition of informal hand-craft ubiquitous to Ethiopia – a knack for fixing things is a useful and common skill no doubt developed through use.
Nevertheless, whether is it power loss or tool failure, the most reliable improvisation becomes the hand-tool – oddly at times even more efficient than the power tool. These simple acts of ingenuity typically seem ludicrous to the outsider, where in Ethiopia they are integrated into the fabric of creative subsistence.
In fact, tools are all too often broken – typically by overuse or simply by virtue of environmental conditions. The repair, modification, or simply invention of a tool constitutes what I fondly call the MacGuyver Methodology, a state in which a creative manipulation of limited resources becomes the only skill towards manifesting or materializing a goal. Thus, the most robust tools are often the least technological extensions of the body: simple hand tools, a string tied to a shovel to reduce labor – even the body itself becomes employed for problem-solving. The Ethiopian proverb, “Yala bala bet-u, eine dim-a satu” (“The tool is best used in the hands of its owner”), expresses at once this relation of tool and body, and perhaps also the impulse to protect one’s own limited resources.
Zegeye Cherenet has noted that the constraints within Ethiopian culture have allowed Ethiopians to boast a very uncommon skill: “I know how to use little. I know how to not consume.” It is this informal improvisation – a culturally embedded outcome from lack – which Ethiopians do best; and it is this skill which should be understood as a means for achieving a truly local, economically and environmentally sustainable praxis in Ethiopia. Rather than understand this skill merely as an abstract philosophy, however, we will attempt to understand how it may be harnessed as a design methodology.
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The SUDU – the Sustainable Urban Dwelling Unit – is a low-cost housing prototype built with local materials and local labor, utilizing techniques analogous to vernacular Ethiopian building technologies. The premise of the project is to design for a combined goal of environmental and economic sustainability.
1: By utilizing the cheapest of Ethiopian resources (soil), and the skill base presumed to be present in working with soil construction technologies, the construction industry in Ethiopia can thereby reduce its reliance on imported, expensive, and high energy-intensive building materials such as steel and concrete. Further, through this expense reduction, the SUDU may become a model low-cost housing unit for the urban poor.
2: One of the most challenging present problems for Ethiopia, and Addis Ababa in particular, is the tremendous deficit in housing for the urban poor, coupled with the statistics of population growth in Ethiopian cities. This is reflected in the ubiquitous informal housing, comprising perhaps 80% of the built environment of Addis. While the most common vernacular, Ethiopian construction method – construction with Eucalyptus and mud – is an economically and environmentally sustainable method of construction, the great limitation of such constructions is that they do not address the problem of necessary of urban density, the limitation of the land available and the expense of this land.
Thus, this vernacular technology has been more recently replaced by large urban housing projects of reinforced concrete – massive edifices of concrete and steel, which neither offer a model for frugal, environmentally or economically sustainable construction, nor do they offer a low-cost alternative to housing, as driven by the expense of their construction. These constructions are being built all over Addis Ababa, displacing massive numbers of squatters in informal housing networks, who cannot afford to be relocated to such housing units, and are therefore relegated to the growing numbers of urban homeless.
The SUDU in an exploration of a “medium ground” between single story informal dwelling and massive scale urban density, as studies have shown that even a 2-story urban density dramatically impacts urban density.
3: Thus, the goals of the SUDU are to build to two stories in soil – a significant challenge without the aid of imported steel, concrete or milled lumber.
By adapting local soil knowledge to the production of soil stabilized tiles, however, it is possible to introduce the technology of timbrel vaulting (thin-shell vaulting technique developed in Spain) to allow floor and roof systems of pure compression, without the excessive requirement for such imported materials. The timbrel vaulting technology is a radically minimum-material construction system, by virtue of its catenary structural efficiency and by virtue of the use of plaster mortar, which eliminates the need for comprehensive formwork.
4: My role, as the ‘visiting expert’ on timbrel vaulting construction, is to ascertain if/ how timbrel vaulting can be considered as an ‘appropriate building technology’ for the skill base of local workers, if/ how such a method of construction can be trained in Ethiopia, and also what are the risks involved in the introduction of a new technology of unreinforced structural masonry, both for the safety of workers and the ultimate reliability of structural masonry shells built by untrained labor.
Photo by C. Lippuner