Adobe: The Most Sustainable Recyclable Building Material
When building for a more sustainable world, the materials you choose undoubtedly play the biggest part in minimizing your project's carbon footprint. Building a wall out of plastic bottles, for example, prevents them from adding to the hoard in a landfill. However, there is a material used for centuries throughout the world that tops all the rest when it comes to sustainability: adobe.
When we think about sustainability in construction, we must first think of the project's function. For many builders, the norm is to use materials that will last for thousands of years, therefore prolonging utility. Adobe on the other hand, is one of the materials whose production, lifespan, and disposal results in net-zero carbon emissions. Here, we will highlight the use of adobe in Araukaria Arquitectura's project El Encuentro on the outskirts of Bogota, which showcases the material's thermal and aesthetic qualities as well as its environmental capacities--namely withstanding Colombia's humid, rainy climate
To use adobe in regions like this, there are two possible techniques: rammed earth and adobe blocks. Adobe walls, unlike rammed earth, can be built in narrower proportions. In fact, a wall of 25 cm is able to absorb heat to warm the interior while rammed earth walls, which can be built to over 60 cm width, provide cooler spaces. Compared to mass-produced bricks, adobe blocks are made on-site, rendering blocks that vary in both color and shape and that ultimately give adobe its unique characteristics. On top of the cosmetic advantage, adobe also has economic advantages over bricks as it can be easily remodeled or repaired.
To fabricate the adobe blocks, it's first necessary to choose the right type of earth. If it's too sandy, the blocks will crumble. If it's excessively wet, they won't maintain their shape. The ideal mixture should be clayey, making for a malleable but structurally sound block. As mentioned before, because adobe blocks are made on site, the ground where the house will be built is just as important as the earth used to form the block. Ignoring this element will increase the project's costs--and environmental impact. The quality of earth in and around Bogota is optimal for the previously mentioned 50cm technique and this is exactly what El Encuentro's creators were counting on.
During the process, in this case done the artesian way, oxen mix up the earth with their hooves while water is added periodically. Sand is added to balance the mixture and to increase malleability. Afterwards, horse manure is mixed in as well, but only from horses that have been in a pasture as manure from stables contains too much sawdust. The manure increases the mixture's permeability thanks to its urine content according to Clarita Sanchez from the National University of Colombia's Earth Studies department. Afterwards, wheat chaff is added to provide structure to the blocks. In parts of the world where wheat isn't readily available, patula pine is used instead.
After forming the blocks to the desired shape and size, they must be left on the ground where they were molded for the pre-dry stage. This step of the process can last 1 to 2 months, depending on the moisture and humidity in the air. During this time the blocks can either be covered or left exposed to the rain, which adds to adobe's characteristic texture.
The mortar used to cement the blocks together depends on a project's individual criteria. The local technique uses earth, however, for El Encuentro, the creators decided to use a cement-adobe mixture that would add to the structure's longevity.
The local wisdom says that you need to have "a good hat and boots" in order to build with adobe, meaning that the base, or "boots," of the wall should be isolated enough so that exposure to the rain doesn't compromise the adobe mixture and the roof, or "hat," of the house should divert the rain away from the structure.
As good as the "hat" and "boots" of an adobe wall may be, if a pipe bursts within the structure, the adobe will act as a sponge, soaking up the water until it is completely saturated. If left unattended, this will eventually disintegrate the material, as happened to one of El Encuentro's walls. Luckily, another wall quickly replaced it thanks to the generous supply of blocks set aside for the project per the architect's recommendations. And what became of the remains of the destroyed wall? They were added to the house's garden and, upon disintegrating, became fertilizer for the grass, an optimal demonstration of the zero-waste properties of adobe.