Clemens Plank in conversation

Compacted Clay


#08 Konzentration


Frank Haas


Alexander Kofler



The Vorarlberg native Clemens Plank is a freelance architect and lecturer at the University of Innsbruck. He builds houses from materials readily to hand, creating jobs where they are needed most. An interview on a brilliantly simple solution that is still little known. But hopefully not for long.

Clemens, you're building an educational center using rammed earth. Martin Rauch, a gifted artist from Vorarlberg, optimized that traditional construction method which you are using. When completed, the structure will be less vulnerable to earthquakes than conventional buildings. Can you explain your thinking for us in layman's terms?
What makes it special, actually almost miraculous, is that you are effectively creating an edifice from soil alone. From stony material in a range of consistencies that you mix with loam or that is already mixed with it. Sometimes you can simply use the unadulterated soil you’ve excavated, but other times you have to add a little gravel or clay to make it easier to shape. You then cast the material in roughly 12 centimeter thick layers in the kind of mold used to create concrete blocks. Each layer is then compacted – either manually or mechanically. The wall then rises layer by layer until it reaches the desired overall height. And at this point the mold or formwork can be removed. The compacted material is almost as solid as concrete. The compression creates bonds between the rock particles, cementing the material together. You can hammer nails into it, just as you might in a concrete wall. And when it rains, a little of the clay washes o the surface, exposing the stony material beneath. This forms a natural barrier to erosion and stops water seeping further into the wall. In the olden days people often used this technique to build houses, in Europe and beyond. Martin Rauch says it was originally the favored method of the poor. There are still homes in Germany and Italy that used this technique. But most people don’t realize, because the exteriors are now covered with normal plaster.

clemens2.jpgClemens Plank

The individual layers of compacted clay are still visible in the freshly rammed wall

And how does that ancient construction method work without being compacted?
In the traditional technique, you shape mud into a standard brick shape. In Peru they don’t fire these bricks – they simply let them dry before setting them in place. But the buildings are prone to collapse because the bricks are not bonded firmly together.

I thought this method of construction was only feasible in Peru, or at least using Peruvian loam or clay. But that's not true, is it?
Correct! This method actually works anywhere. In Yemen for instance they have erected entire cities this way, including ten-storey buildings that are classified as world heritage sites. It’s also common in Asia. The Peruvian capital Lima has ancient walls that the Incas presumably made in a comparable way.

And what innovations have you contributed?
We are really only reviving an age-old building method. Adding some modern know-how makes some people view it as an architectural wonder.Which it isn’t by any means. Today we do the compacting with machines powered by compressed air, while ancient builders did it manually by beating the earth with wood or stone. There's nothing to stop people compacting by hand today, but that would only drive up the cost of labor. Our calculations show that our construction method for the Wayna Warma center cost 350 Peruvian soles, or roughly 100 euros, per square meter of wall. Of these 350 soles, approximately 50 were material costs. The other 300 were for labor. So ordinary manual labor that basically anyone can do makes up 80 percent of the total. The labor-intensive nature of this process makes it prohibitively expensive in Austria, where wages are relatively high – but materials are far, far cheaper. The use of machines doesn’t change this equation.

The land purchased for the Wayna Warna educational center in Cusco is rich in clay
The architecture provides for three types of functional spaces – communal areas, classrooms and administrative offices

But the equation makes sense in Peru?
If I, for instance donated 10,000 euros to build this educational center using this method, 9,500 euros of that would pay laborers living at a minimum subsistence level and 500 euros would be for materials – basically added gravel. If the whole thing were to be built in reinforced concrete, the money would end up going to companies that supply concrete and steel. If we were to build it with conventional fired bricks, the money would go to the brick industry. And the brick, steel and concrete suppliers are typically owned by foreign corporations. In other words ultimately, most of the money would make its way back to the United States or Europe. By contrast, using rammed earth means that all the money stays in Peru.

So you are doing two good deeds – for the children and the people involved in building the center?
Exactly. Initially, looking at this as an architect, I found the construction method interesting from an aesthetic point of view. The buildings are pleasing on the eye. And recently we came to realize that the project as a whole is not just about creating a positive and suitable environment for children, and doing so with a charity that has a well conceived strategy. It's also about using these funds from European donors to provide jobs for ten workers, and covering the cost of living for ten families, for the duration of the two-year project. What's more, the workers are learning a new technique which, while utilizing materials normally used to make bricks, withstands earthquakes better and is far more sustainable. We aimed to erect three buildings in this project. The first one was constructed by the laborers with our assistance. Using the tamping machines, formworks and other equipment we provided, they were then able to build the second on their own. As a consequence, a body of know-how has now been established in Peru. The third building may not have been started yet, but work will commence as soon as the funding is secured. The next step would be to share the know-how and machines here with other local families so that they can build houses the same way. A traditional mud-brick structure needs a lot of maintenance and has to be reworked once a year. But a rammed-earth house will stand for a century, provided you keep the roof sealed. Preventing leaks is the key to success.

The center was built where needy families live: on the outskirts of the World Heritage Site Cusco

You said that rammed-earth buildings are less vulnerable to earthquakes than brick structures. What other benefits do they offer?
They are very eco-friendly. For instance, the soil excavated for the foundations is used for the walls. What is more, they cause no environmental pollution and there are no recycling problems. In terms of climate control, they make the building more comfortable because the walls regulate the humidity. And that is a real plus for the residents.

And who should we be approaching with this construction method now?
That’s a good question. First of all, the aid organizations. We are currently receiving funding for applications that involve the use of rammed earth. Why? Because financiers recognize the common sense and sustainability of this method. If our sole concern were to erect an educational center, I could use low-cost corrugated iron or opt for traditional mud bricks or reinforced concrete. But that's short-sighted, and it’s precisely here that we need a paradigm shift. We need to make it clear that the building and its construction are the first steps in the aid project.

Many different people were involved on the construction site. Why do you think you worked so well as a team?
The method helped create a bond between us. When you interact so long on a project like the educational center, it almost becomes a form of meditation. As an architect, I was thrilled to see the architecture, the building, become a catalyst: the social side of things isn't limited to what will happen inside the building later – its genesis and evolution are relevant too.

What did you learn that you can tap for your work as an architect and the college courses you teach?
That’s a difficult question. Leaving aside considerations based on the costs incurred and advantages generated – i.e. how my company and university will benefit – I can say this. From my personal point of view it's fantastically rewarding to work on a meaningful project like this. That's the most basic benefit. In addition, as an academic I've acquired an incredibly interesting project that I can use in my research and the courses I teach. The building we created there both illustrates the potential and throws up challenges. For example, structural engineers and analysts will be confronted by a brand new material. Until now they have known little but steel and concrete. Then there is a geographer who was assigned by the university to supervise the project with me. And he is fascinated by its social implications and the questions that inevitably arise. How is the educational center panning out, what impact is it having on the charity's activities? The center cost a lot of money to build, and it has a strikingly modern design. Would erecting something like this in a deprived area spark an outpouring of anger? Or would it be viewed as a boon, because it testifies to an appreciation of the material used and the children who will use it? As we see it, this project embodies the essence of architecture: man as the origin of the objects that surround him.

Finally, what are your hopes for the future?
That the aid organizations realize the added value of this construction method and invest in the architecture of their projects, for example in Africa and Asia – that would make a lot of sense.

Frank Haas is head of brand strategy and communication at Gebrüder Weiss and editor-in-chief of Atlas.

The children can already use some of their new rooms
In Quechua, the language of the Incas, the word “wayna warma” means “adolescents.” And it is also the name of a Peruvian initiative that supports local children and teenagers from poor families. Launched in the 1990s by the Camacho family from the city of Cusco, the organization takes these young people under its wing on a long-term basis, offering them a quiet retreat, educational opportunities and a place to play, dance and be creative. Discovering that it was outgrowing its original leased premises, the charity purchased a plot of land for an educational center. The center itself is currently being built with the aid of funding from Europe.
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