Mud and Wood: Materials in dialogue

 

"Palo a pique" walls in a house in

Chiquitanía, Bolivia.

Credits: Jorge Tomasi

Earthen construction technologies involve a wide array of techniques, practices, knowledge and the use of different materials in their interaction with the soil, socially and historically modelled in response to the dynamics of the conditions of existence. Within this heterogeneous group, we can recognise techniques such as adobe masonry, tapial from the use of compacted earth in formworks, or the wefts of vegetable fibres filled with mud, as in wattle and daub, and many others, each one with its own diversities in the ways of doing things.  In different ways, all of these techniques involve, or may involve, the use of wood, which reveals a dialogue between the knowledge and practices associated with the treatment of materials.  

In some cases there is a direct interaction between wood and earth in the shaping of walls or roofs, while in others the materials are related in different parts of a construction. It is even worth considering the use of wood in the tools needed for moulding or for ramming and tamping, as is the case with adobe or rammed earth. Repeated connections between the two materials are recorded in many building cultures around the world and are based on the compatibility of their behaviour. At the same time, their particular characteristics present specific challenges for conservation, in relation to the different types of agents that can affect them. In this sense, the study of both materials, and the resulting architectures, should not be treated as separate fields.

The group of techniques known as wattle and daub involve the closest interaction between these materials. Under different names, such as torchi, quincha, palo a pique or bahareque, among others, there is a large universe of procedures embedded in building cultures, with multiple types of plant fibres and treatments, for the construction of walls that are usually between 10 and 20 cm thick, even enabling high-rise buildings. Generally speaking, these techniques involve the assembly of a main wooden structure, with a secondary weft, made of flexible plant fibres, which are braided into the main structure.

Reinforced quincha walls in a house in

Villa El Perchel, Jujuy, Argentina.

Credits: Jorge Tomasi

Finally, this wooden system is filled with earth in a plastic state, which is mechanically fixed in the fibre weft, and then plastered. The soil is also often stabilised with plant fibres in large proportions, up to a majority, as is the case with light earth techniques. Most recent research has developed new solutions within wattle and daub with the use of reinforced wooden frames, which have braided canes inside them. These prefabricated frames are then anchored to the timber structure. This wide range of techniques involves the bringing into play of diverse knowledge for the processing of wood and the development of the joints, together with the knowledge associated with the correct execution of the clay mortars for the filling.  

Outside wattle and daub, an extremely interesting case in the interactions between wood and earth is represented by the adobillo technique, characteristic of the buildings in the city of Valparaiso, Chile. In this case, there is also a wooden structure, with vertical pieces placed every 50 to 60 cm, between which adobe bricks are placed, with a thickness of around 15 cm. These specifically shaped adobe bricks have notches at their ends, which allow them to be fixed to the rods contained in the wooden structure. In recent years, a number of very important conservation actions have been carried out in this technique by various researchers and professionals in Chile.

Wooden collar beam in an adobe wall, supporting

the roof structure, in a 17th century church,

in Uquía, Argentina. Credits: Jorge Tomasi

A very relevant field in which articulations are established is in the use of earth for the walls, either through the use of rammed earth or adobe, and the roof structures. The resolutions of the roofs assume different conformations, with A-frame trusses structures as one of the most relevant, with a large presence throughout the Andean area in South America. The connection between walls and roofs, in these cases, is an extremely important challenge to avoid structural damage to the supports, and to achieve a homogeneous behaviour in the constructions. A common solution is the placement of a wooden perimeter beam, which can be shaped like a staircase, at the top of the walls, on which the roof elements rest. In this line, it is also very common to place specific wooden reinforcements, in the form of braces, on adobe or rammed earth walls, to repair cracks, reinforce corners and junctions or to link sections of different characteristics in the walls. Indeed, the most recent research related to the conservation of earthen architecture recommends the use of wood for this type of reinforcement, including even the incorporation of upper beams of this material for linking walls and roofs.

The "adobillo" technique in the upper station
 of the Ascensor Concepción, restored in
2017-2019, in Valparaiso, Chile.
Photo credits: Carmen Gómez Maestro

Disciplinary specialisations often lead us to analyse the use of these materials independently, which limits the possibility of looking at the different ways in which they relate to each other, improving their respective behaviours or generating different pathologies. In this framework, it is a good idea to focus on vernacular builders, and their historical and current architectures, who deploy their practices and knowledge in an integrated way, recognising technical overlaps.  

Blog by Jorge Tomasi, an architect and researcher based at the Consejo Nacional de Investigaciones Científicas y Técnicas (National Scientific and Technical Research Council) in Argentina. His research interests are in the relationship between anthropology and architecture, earthen building and vernacular architecture in the Andean area, in Argentina. He is also on the Advisory Board of the Endangered Wooden Architecture Programme.