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Cob in Spain Vernacular Heritage and Earthen Architecture: Contributions for Sustainable Development – Correia, Carlos & Rocha (Eds) © 2014 Taylor & Francis Group, London, ISBN 978-1-138-00083-4 Cob in Spain C. Mileto, F. Vegas López-Manzanares, V. Cristini & L. García Soriano Instituto de Restauración del Patrimonio, Universitat Politècnica de València, Valencia, Spain ABSTRACT: Spain is characterized by the extensive use of earthen traditional building techniques. Several variants of rammed earth, adobe and half-timber appear in all the Spanish geography, in dwell- ings, in military and in monumental architecture. Cob, so frequent in traditional architecture in Africa and other European countries, seems to be absent in the Spanish territory. Nevertheless, on-site work made during some research projects endorsed the discovery of several examples, and have confirmed the use of this traditional building technique in Spain, despite the lack of bibliography on this topic. The text aims to gather the up-to-date existing data on historic and traditional buildings in cob in Spain, its variants, its place, and the typology of buildings built that way, but also the future possibilities of this technique for contemporary architecture, due to its low cost and sustainable principles. 1 I NTRODUCTION study of this technique; its situation in Europe and specifically in Spain, and a case study strategy Earthen architecture, practically in all its constructive using qualitative methods. The case study selected techniques, can be found in most parts of Spanish is a particular type of construction: the Valencian territory. Some of these techniques, such as rammed barraca (a typical dwelling of vernacular architec- earth, adobe or half-timber, are often used in the con- ture in the Valencian countryside). A total amount struction of traditional Spanish architecture. of fifty of these barracas has been studied in order On the other hand, constructions with the cob to extract conclusions about its construction tech- technique, known as pared de mano (or heaped-up niques. A combination of sources was used fol- earth) are not so common and perhaps for this rea- lowing a multi-method approach and site visits: son this technique has not been studied much in published literature, collection of local data, field this territory. In the framework of some research studies with sites observations, both for the Span- projects about vernacular architecture in general, ish and European cob constructions, as well as for and earthen architecture in particular, such as the the particular case of the Valencian barraca. The project ‘The restoration of rammed earthen archi- study of all these data, obtained from different tecture in the Iberian Peninsula. Criteria, techniques, sources, has permitted to extract general conclu- results and perspectives, ref. BIA 2010–18921)’, sions about this type of earthen building technique granted by the Ministry of Science and Innovation and its future possibilities in the search for a more under the National Grant Scheme for the year 2010, sustainable contemporary architecture. and ‘VerSus. Lessons from Vernacular Heritage in Sustainable Architecture’, granted by the European Union (Culture programme nº 2012–2792), differ- 3 THE COB BUILDING TECHNIQUE ent examples of this building method in traditional Spanish architecture were studied. The use of cob can be found in a great deal of This study is relevant, because up to date there traditional European architecture. In many Euro- has not been almost any information published pean countries buildings constructed using this about cob in Spain, neither locally, nor even less technique can still be found, such as France, Italy, nationally. Therefore, the goal is to make a gen- Germany, Belgium and the Czech Republic (Patte eral reflection about it that will provide an overall & Streiff 2007), but it can be defined as the main image of the characteristics of this constructive representative of earthen architecture in England technique in our territory. (Keefe 2005). Furthermore, this technique is also found in many developing countries, like in simple rural houses in Afghanistan or cities with many- 2 METHODOLOGY storied buildings like in Yemen (Houben 2006). It is a technique in which the basic materials used The research on which this paper is grounded, are a mixture of earth with fibres and water. This addresses a deductive analysis based on a general earth must be taken from the subsoil, the layer of 301 material underneath the upper organic layer and on top of the base (Watson & McCabe 2011). Then, this earth is mixed on the ground generally with vegetable fibres (such as straw or even grain in some cases) and water, to form a malleable clayey mixture that is easy to handle. The mixing is usually done by feet and the amount of water added varies in each case, depend- ing on the amount of water present in the earth and the preferences of the builder. Some builders prefer to add large amounts of water to mix it, and then leave the material to rest for some time, in order to allow it to dry before placing it on the wall, whereas other builders prefer a dryer mixture from the outset, to avoid too many unwanted retractions caused by the drying of the material. Therefore, a deciding factor in the success of constructing with this technique is the builders’ practical experience and their knowledge of the intrinsic characteristics of the material. Once it has been kneaded into a uniform mix- ture, it is fashioned into big balls (in some cases Figure 1. Construction of a cob wall on a masonry also known as pelladas), which are piled on the base, in France. (Credits: Claire-Anne de Chazelles). wall, tightly bonded with each other. The walls built in this way in successive layers can be quite thick (between 40–50 cm and 200 cm), and end up with a monolithic appearance (Guillaud 2008). In features of the construction are also peculiar to the the building of these walls it is necessary to respect area and vary between the different countries and the height of the strip of damp earth that is applied even different regions in the same country. every day, about 50–60 cm, so as to ensure that the Thus, in Portugal, this technique is known as previous layer will have acquired the necessary terra empilhada, which means piled earth, directly consistency and resistance to support the amount reflecting the layout of the material during the of material placed on top of it (figure 1). building process. In Italy it is called massone, and Thanks to their good physical properties, these even today this constructive technique is constantly walls can be erected without having to use form- used in the center-east of the continental part of the work, although in some cases this method has been country, specifically in the regions of Abruzzo and used in the building process. Apart from not need- the south of Marche, and there are other local terms ing formwork, another clear difference with the to define the technique in these regions such as mal- rammed earth technique is that the material does tone. In France it is called bauge, and in Spain it is not need to be rammed during the constructive known as pared de mano or muro amasado from the process. The force used in using balls of earth piled act of kneading and shaping the balls by hand dur- on top of each other during the building of the wall ing the construction process, and is also called tierra is sufficient to guarantee that the material is prop- apilada. It is also found as chamizo in Spain, but in erly compacted. Besides that, the large proportion this case, it usually refers to walls made with a sub- of water added to the mass in making cob walls, as structure of timber or cane on which the kneaded opposed to the small amount of water necessary to earth is placed. In German it is known as weller and make rammed earth walls, is the fundamental rea- the word “cob” is the Anglo-Saxon term for this son why vegetable fibbers are added as degreasers technique (Correia 2008). The latter is probably the and frames to prevent retractions that could occur most common because of the important presence during the drying process of the material. of this constructive method in Great Britain. 3.1 Terminology 3.2 Variants of the constructive technique Another important aspect is to become famil- Different variants of this technique can be found iar with the different terms used for this building in European territory. The variants are not so method depending on the geographic location. The very different as regards the material to be used terminological richness gives a clear idea of the (although the proportions of the mixture may abundance of slight variations that can be found. vary according to geographic zones, the principal In each place, the technique receives a concrete components that form it are usually the same), name and it is, in a way, a reflection that the typical but the application of this material during the 302 building process of the wall can be different and 4 COB CONSTRUCTION IN SPAIN the fact that it may contain reinforcement or auxil- iary substructures. Cob is probably the least studied of all the differ- The simplest version is the one built only of ent construction techniques with earth that can be “balls” of kneaded material, placed on top of each found in Spain. As previously mentioned, this is other, to make the wall little by little. If the mate- due to the fact that there are not very many exam- rial used has good properties, this process is carried ples of this constructive method, since it has been out without formwork.
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