Rebouilding After A Disaster: Clay or Cement?

Author: Kurt Rhyner, Architect, Dr. Prof.

The reconstruction of several hundred houses in Guatemala following the 1976 earthquake marked the beginning of what eventually became Grupo Sofonías and the EcoSur Network. Three months after the catastrophe, which claimed approximately 23,000 lives, we began studying reconstruction in the rural department of Salamá. Our task was to find ways to promote affordable solutions for low-income families while improving the resistance of their homes.

“For centuries, people have built with adobe, using the earth beneath their feet to make sun-dried clay bricks. It only requires time and physical effort. However, adobe and fired clay tiles were blamed for much of the damage.

There was widespread fear of earthen construction and a feeling that it should be completely prohibited. Most houses in the affected areas were made of adobe, and most of the damaged houses were also made of adobe. Many of the new cement-based structures had performed better during the earthquake.

Nevertheless, Caritas Switzerland decided to dedicate part of its aid to supporting reconstruction with local materials, in an effort to promote sustainable solutions. Caritas Guatemala, however, initially received the project with skepticism.

The influential local church did not oppose the plans; in fact, some priests and nuns welcomed the idea of working with ancestral traditions to improve people's skills.

The project aimed to adapt traditional knowledge of adobe construction by applying engineering principles and the findings of a United Nations study following the 1970 Peruvian earthquake. Furthermore, damage assessments in the villages surrounding the hardest-hit areas of Salamá showed that the earthquake had destroyed not only adobe buildings but also many cement-based structures.”

The project started slowly, but an increasing number of villagers decided to learn about more earthquake-resistant construction, and several hundred houses were built. A university assessment 24 years later found that all the houses were still occupied and in acceptable condition. It also emphasized that reconstruction involves much more than simply putting up a structure.

The evaluation team concluded that it is possible to build houses using traditional clay in seismic areas, provided that improvements are made. It recommended that such projects be firmly planned and organized in harmony with the culture and identity of the population, the surrounding natural environment, and traditional architectural expressions.

Almost 50 years after construction, some houses have suffered from a lack of maintenance, but nearly all remain occupied. Most have been sold or passed on to the next generation.

CAN EARTHEN HOUSES WITHSTAND EARTHQUAKES?

Of course, they can, provided they are built correctly. However, it must be clear that there is never complete safety during a major seismic event. The accepted objective among disaster specialists is to prevent buildings from collapsing, even if they sustain damage.

In fact, every earthquake a building survives leaves some minor damage. If that damage is not detected and repaired, it may become the trigger for failure during the next earthquake. There is good news for clay buildings: repairs are easy and affordable.

Injecting liquid clay into cracks can actually improve the strength of the wall.

There are many publications and manuals explaining how to improve earthen construction, particularly adobe and rammed-earth buildings. Protection against moisture is crucial: “good boots, a wide roof, and a coat.” Solid foundations and footings, probably made with stone and perhaps some cement, provide a stable base and protect against moisture. Wide roof overhangs and plaster protect the walls from rain.

THERE IS NO GOOD OR BAD BUILDING MATERIAL, ONLY MATERIAL THAT IS USED WELL OR POORLY

Earthquakes cause terrible suffering. Buildings collapse, and people are killed or injured. When this happens in a culture where earthen buildings are common, comments tend to condemn adobe and rammed-earth construction, without considering that cement-based structures have also collapsed and caused deaths.

In recent years, major seismic events in Haiti in 2010 and Ecuador in 2016 struck areas where cement-based structures predominate, resulting in enormous loss of life. In both countries, Grupo Sofonías and the EcoSur Network analyzed the situation and led reconstruction programs in cooperation with the Swiss Agency for Development and Cooperation (SDC).

Most popular construction in the developing world is unsafe. Craftspeople learn from “masters” who themselves have never received adequate training or knowledge. The same mistakes are repeated again and again, at the expense of homeowners and putting residents' lives at risk.

Drawing on Grupo Sofonías' extensive experience with dual education, training programs for informal builders were organized. Participants received formal classroom instruction combined with practical experience while building houses. In cooperation with the Swiss agency and local universities, high-quality educational materials were developed for use both in classrooms and on construction sites.

More than one hundred masons and carpenters acquired solid theoretical knowledge and put it into practice, completing the program with an examination and a diploma.

BASIC INFORMATION ABOUT EARTHQUAKE RESISTANCE

Earthquakes place buildings under different types of stress, but horizontal forces are primarily responsible for damage and can cause buildings to collapse.

Masonry walls without additional reinforcement—such as timber, reinforced concrete, or metal—can develop cracks because masonry generally has good compressive strength but low bending strength. This is particularly true of earthen walls.

Depending on the direction of seismic waves, some walls develop mainly diagonal cracks, while others develop vertical cracks.

Tall walls are more vulnerable, especially when they are slender. Second and third floors are at greater risk. Traditional buildings are often constructed with thick, solid walls, frequently incorporating horizontal reinforcement, and may have survived several major earthquakes. Maintenance and repair are key to their resistance.

Reinforced concrete opened up new possibilities, and today many affordable houses are built using a framework of columns and beams, known as reinforced masonry. Walls are often left open to create commercial spaces or garages, while upper floors are filled with any available material without a proper connection to the structure. As a result, there are no solid walls capable of resisting shear forces during an earthquake.

It is common to find buildings where the ground floor has collapsed under the weight of the upper floors.

By moving from reinforced masonry to confined masonry, walls can respond to shear forces and work together with the concrete structure. The basic procedure is to build the walls first and then cast the columns and beams around them, creating an almost monolithic unit. At the design stage, it is essential to ensure a good balance between solid walls and open spaces.

THE ECOSUR NETWORK

The network's main members have accumulated extensive knowledge and experience in the design and implementation of social housing projects, particularly following disasters.

From Guatemala in 1976 to Ecuador in 2016, thousands of buildings constructed with different local materials stand as evidence of this experience. Hundreds of builders have also received proper education and training. Architects and engineers have shared their knowledge as project designers, managers, and instructors in post-disaster situations across Asia and Africa.

EcoSur is committed to supporting programs that improve traditional construction knowledge. Sustainable housing must be affordable, have a small ecological footprint, respect local culture, and be socially accepted.