Gypsum Quarries Used in Valencian Architecture: Past, Present and Future

Gypsum quarries used in Valencian architecture: Past, present and future

V. La Spina Universidad Politécnica de Cartagena, Murcia, Spain L. García Soriano, C. Mileto & F. Vegas López-Manzanares Universitat Politècnica de València, Valencia, Spain

ABSTRACT: The historical use of natural resources closer to a center population in construction of buildings is an ancient practice. It responds to a maximum sustainability criteria based on common sense and reduction of any added cost and it defines the constructive characters both of vernacular architecture in rural areas and civil architecture in urban sets. Historically, in the province of Valencia gypsum has been a widely used material motivated by economic reasons due to its simple extraction, traditional production process and application as construction material, but mainly because of the abundance and proximity of gypsum deposits. The aim of this paper is to describe the historical quarries of the province, the traditional local manufacturing process and the different applications of gypsum. Thereby, we can rescue the traditional industry from obscurity and propose the use of gypsum in restoration interventions but, also in contemporary architecture, applying the same sustainable and ecological criteria of the past.

1 INTRODUCTION 1.1 Brief foreword about gypsum The gypsum is a sedimentary rock chemically made Gypsum is a raw material that has been widely up of crystallised calcium sulfate (CaSO4 2H2O) used in construction since olden times, as we can and the gypsum plaster is the product obtained see from the archaeological remains of the city of from calcining and grinding it, which sets quickly Catal-Hüyuk (6600–5650 BC) in Turkey. In the when mixed with water. case in point, its abundant presence in historic and Specifically, gypsum is an evaporite rock with traditional constructions in the province of Valen- a crystalline structure with low surface hardness cia is mainly due to the existence of numerous gyp- and which can be found in nature in several forms sum deposits, thanks to which its use was simple, and in three possible phases: gypsum, basanite and immediate and cheap. Added to this is the simplic- anhydrite, often accompanied by impurities of ity of the traditional production process of pow- clay, sand and other sulfates or salts like carbon- dered gypsum and the ease and speed with which it ates and chlorides. can be used as a construction material. The calcination process consists in dehydrating However, this feature was unfortunately lost with the rock by eliminating whatever humidity and the advent of modern industrial products, which have water it contains at temperatures that can go from different features and properties from the traditional 120º C to 900º C. The dehydration may be partial ones, and the progressive abandonment of rural or total, depending on the temperature and the areas, which has led to the end of historic gypsum pressure to which the rock is submitted, and up to quarries and the traditional use of this material. five phases of gypsum can be obtained with differ- Therefore, the main aim of this article is to enu- ent rehydrating degrees: merate the different uses of gypsum in Valencian architecture, comparing and relating them with – Gypsum. This is the stable phase that represents other Spanish and European provinces; to describe both uncalcined and rehydrated gypsum. the traditional manufacturing process; and, above – Hemihydrate. This phase is obtained by partially all, to spotlight the historic gypsum quarries in the dehydrating the hydrated calcium sulfate at a province of Valencia on the basis of the informa- temperature slightly over 100º C. tion available in the bibliography and historical – Anhydrite III or soluble anhydrite. At between treatises and the study of the geological character- 150º and 200º C gypsum is totally dehydrated istics of the gypsum deposits in the province. but still contains a variable amount of water.

411 The product obtained is very thirsty for water and unstable, so it quickly becomes hemihy- drated just with the moisture in the atmosphere. – Anhydrite II or insoluble anhydrite. This is obtained at temperatures over 300º C by exo- thermal transformation and is more stable than anhydrite III. Natural anhydrite belongs in this variety. – Anhydrite I. It is obtained and is stable at temperatures over 1200º C, but when it cools, it becomes anhydrite II. At over 1400º C it turns into calcium oxide and sulfuric anhydrite, but Figure 1. Details of the façades in the historic centre of the presence of impurities can make this trans- Valencia with gypsum renderings (La Spina). formation occur at 700º C, and if the impurities are clay, hydraulic gypsum may be obtained. and for ornamentation, decoration, etc. in differ- Hydration of powdered fired gypsum takes ent forms, styles or manifestations; to make all place when it is mixed with water, forming a viscous types of interior partitions: solid walls made with paste that sets when it undergoes a physicochemical formwork; brick walls or partitions and masonry process where a reconstruction of its micro—and bonded with gypsum mortar, as well as stairs or macrostructure occurs, that is, a hydration-crys- timbrel vaults; traditional jack arch floors with tallisation and hardening of the paste due to an timber joists and superior pavements; false ceilings increase in resistance and changes of state. During or faux vaults in collaboration with wattle or little this process, apart from undergoing a considerable wooden planks and built-in furniture for dwellings increase in temperature, the resistance and the ini- such as benches, shelves, olive bins, cupboards, tial volume augment in a very short time. handrails, fireplaces, etc. and architectonic elements like frontispieces, windows, spiral staircases, ribs of groined vaults, chimneys, etc. (Giner 2007); 2 GYPSUM IN THE TRADITIONAL to make constructive elements with structural func- HISTORIC ARCHITECTURE OF THE tions: pillars or reinforcements for rammed earth PROVINCE OF VALENCIA walls (Vegas et al. 2013); to protect and insulate the flat part of roofs made with boarding or wire net- Gypsum is a material that has been widely used in ting. And it was even used, when preparing works, the construction of many architectonic elements for making models, tests for stone cutting or bond- over the centuries. Nevertheless, the view offered ing girders, joists, etc. in historic construction treatises does not always coincide with reality. As an example, some treatise writers consider that gypsum cannot be used in its 2.1 Some outstanding cases in Valencian natural state to erect buildings because it has the architecture drawback of being soluble in water, despite the fact Many of the uses of gypsum mentioned above that in Sicily, for instance, in areas rich in gypsum, are also common in other Spanish and European traditional constructions are commonly found in regions and cities, although few stand out for their which gypsum is used as the stone material in fab- particular use in traditional historic architecture as rics, even in foundations in direct contact with the much as in the province of Valencia. This is the ground (Mami 2006). Other treatise writers sus- case of exterior gypsum renderings in residences tain that black gypsum, obtained by intermittent in the historic centre of Valencia, both palaces and calcination in layers, can only be used as a ferti- modest buildings, which give the urban image of liser in agriculture, another of the many uses of the city a unique appearance (fig. 1). Other Span- gypsum. On the other hand, Juan de Villanueva ish and European cities and towns with historic (1827) affirms in his treatise that gypsum is one of external gypsum renderings are, for example, the most useful and easy to use materials known Cuenca, Madrid, Albarracín and Paris (La Spina for the construction of the dry parts of buildings. et al. 2013a, b). However, its use in the province of Valencia was Another example are the wooden joists and not limited exclusively to those specified in the jack arch floors that can be found both in historic treatises or for the interior plastering of all sorts urban buildings and vernacular constructions in of buildings, as is the case today. Concretely, gyp- the province (fig. 2). Furthermore, in rural areas sum has been used for interior rendering, but also the upper pavement is still often made of gypsum, for the exteriors of palaces and humble abodes, as is the case of Albarracín (Teruel).

412 Figure 2. Jack arch floors with gypsum vaulting (La Spina).

Figure 4. Geological map of the gypsum deposits in the province of Valencia. Grey: Miocene and black: Keuper (La Spina).

surrounding areas contain an abundance of lime- stone, nearly all the buildings are made with gypsum, Figure 3. Façade of a traditional construction with because less timber is used than with lime: timber gypsum pillars and undulating reinforcement of rammed is so scarce that the inhabitants have to use longer- earth in Rincón de Ademuz (Vegas & Mileto/La Spina). lasting matters and forget about the solids.”

3.1 Historic deposits and quarries in the province It is worth while mentioning also the structural of Valencia role played by gypsum as the main component of pillars, or reinforcement for rammed earth walls The most important deposits of gypsum in the (fig. 3) in the parish of Rincón de Ademúz (Vegas province of Valencia and their geological charac- et al. 2010, 2011, 2012). The pillars in the vernacu- teristics define the situation and the peculiarities lar architecture of this area are partially or fully of the historic quarries that have been operated made with gypsum poured in a formwork and can more or less uninterruptedly over the centuries. support the weight of even four storeys. Gypsum reinforcement of rammed earth walls has a more 3.1.1 The geological formation of gypsum in the or less undulating appearance on the outside. province of Valencia The geological formation of gypsum is due to the drying by evaporation of salt water and salt lakes 3 DECISIVE FACTORS FOR THE USE or inland seas with no outlets to the ocean, with OF GYPSUM IN THE PROVINCE OF thin sheets of water and the effect of a dry climate. VALENCIA For these reasons, the importance and thickness of the deposits as well as their extension and purity The abundant presence of gypsum in traditional are extremely variable (Reguerio & Calvo 1997). and historic buildings in the province of Valencia In general, gypsum deposits are spread all over is mainly due to the existence of gypsum deposits the surface of the earth and are fundamentally that made it possible to obtain it with ease. Other present in Triassic and Tertiary sedimentary for- decisive factors are the simplicity of the traditional mations. In particular, in the province of Valen- production process, the ease and speed with which cia (Martínez & Balaguer 1998), as in the rest of it can be used or its characteristics and qualities Spain, the gypsum deposits were formed mostly as a material. But the economic factor has often in the Triassic Period (Muschelkalk and Keuper) been crucial too, as we can see from the words of of the Mesozoic era and the Tertiary Neogene era Cavanilles (1795) in the second volume of his book (Miocene) of the Cenozoic era (fig. 4). In the for- about the buildings in Guadalest: “Although the mations of the Triassic System, mainly to be found

413 in the north of the province of Valencia, it is possi- a list of active mines and quarries in Spain, and the ble to find clays, marls and gypsums with alternate production arising from their operation according layers of carbonates and sands in the deposits of to the different minerals and Spanish provinces. In the Muschelkalk (the third Triassic era). In the for- general, the analysis of the data contained in these mations in Jarafuel, Quesa and Ayora, which are sources showed that the mining operation of any from the Keuper era (third Triassic period), apart substance in the province of Valencia was scarce from vivid reddish marls and clays, sandstone and and scantly documented. Either because of the lack gypsum can also be found. In the Tertiary Era, of resources, limited information or the misgivings the distribution of Neogene sediments from the of the inhabitants, mining did not have the eco- Miocene period is widespread in the province, but nomic importance it had in other Spanish provinces. the presence of gypsum deposits is not very abun- However, we found out that at least in the mid 19th dant and in most cases they must be seen as acci- century most of the mining activity that took place dental or local elements of the system, both in the was related with materials used for the construc- area of the Catalan Ibérica-Costero and the Preb- tion and ornamentation of buildings, as was also ética ranges. Finally, at other geological periods the case in the 18th century (Hermosilla 1991). But also the presence of gypsum can be found although only the gypsum and alabaster mines of the parishes in the form of marls (De Cortázar & Pato 1882). of Picassent, Monserrat and Serra were mentioned in 1867, the Anita mine in Benaguacil in 1896 and 3.1.2 Historic quarries in the province of Valencia mines of gypsum and other products in several other As there are no recent studies about historic gyp- parts of the province in 1907. In 1909 and the fol- sum quarries in the province of Valencia, we have lowing two years there are a few more detailed data had to consult different bibliographic sources to such as the name of the quarry, the location, the find out the state of mining in the province. owner, the town, the production, etc. And it was not In the first place, we have analysed historic publi- until 1922 that statistics about gypsum mines could cations where the authors describe in detail places in be found, and in that year 20 were registered in the Spain and the natural resources they contain. This whole province. So from 1923 until 1930 we can is the case of the Irish naturalist William Bowles find all the information about the state of gypsum (1775), who mentions a quarry of red gypsum with mines and, from 1925 onwards, information about white veins at the foot of the Tusal Mountain (south the mills and industrial production. After 1931, as of Valencia) and the very old Niñerola quarry in a result of a serious crisis that affected industry in Picassent, first operated by the Romans and which general and especially substances used in ceramics supplied the city of Valencia and the nearby towns. and construction in the province of Valencia, the The famous Valencian botanist, Antonio José Cav- number of quarries and the extraction of gypsum anilles y Palop (1795), also mentions the Niñerola fell and did not recover until after 1939, although to quarry, because it was very important, but alludes a lesser degree. also to quarries in other towns, such as Sabatò to The existence and operation of a gypsum quarry the north of Murviedro (Sagunto); Alginet in the or mine depends exclusively on the presence of the Alfarp and Catadeu area and the ones in Llosa raw material in the area, and it is very likely that it de Ranes and Vallada, Ayora, Cofrentes, Quesa will be mined illegally, that is, without applying for or Jarafuel, etc. and the politician Pascual Madoz a licence or mining concession, and so not recorded (1845) also speaks of the existing quarries, but com- in statistics or historic publications. Thus a quarry pletes the information with the kilns and factories might always have been operated by a town or its and even the gypsum mills in the province. owners when required, since it was only for their In the second place, we have consulted specific own consumption or use without producing large mining publications like Manual del Minero, pub- amounts of material or generating profit. lished in 1843, according to which in the kingdom Consequently, in order to complete the study we of Valencia the old compact, fibrous gypsum or thought it wise to examine the mines currently in gipso terreo mines were in Murviedro, Niñerola operation and the most recent licences requested. and Manuel; and the reports drawn up by Dan- To this end, we consulted the information con- iel De Cortázar and Manuel Pato in 1882 and the tained in the mining section of the Territorial Boletín de la Real Sociedad Española de Historia Energy Service of the Department of Industry natural in 1926, which describe in detail the gyp- of the Generalitat Valenciana, connected with the sum quarries in Niñerola. Directorate General of Energy & Mining Policies In the third place, we have examined the database of the Ministry of Industry, Tourism and Trade, of the Instituto Geológico y Minero de España, which comprises the quarries registered from 1944 concretely the annual information of the “Estadís- to 1950 and those operating in 2012, according tica Minera de España” for the period between 1861 to the Report on Valencian Mining Concessions and 1940. This annual publication contains mainly of that same year. They were found to be located

414 Figure 6. Traditional construction for producing gypsum located in Gestalgar (La Spina).

24 hours was enough to fire the rock, maintain- ing the heat constant all the time, but it depended on the weather conditions, the quality of the stone, the fuel used and, above all, the skill of the gypsum producers. In general, the firing process was rather irregular, because the upper rocks were usually not Figure 5. Map of the province of Valencia showing the fired enough while the bottom ones were fired too location of the historic quarries (La Spina). much, but this made it easier to obtain multi-phase products with a large content of anhydrite (Sanz 2009) and impurities, depending on the deposit. in the following towns: Chiva, Domeño, Altura, In comparison with the production of lime, gyp- Segorbe, Gátova, Xátiva, Llosa de Ranes, Chelva, sum requires less time and a lower firing tempera- Requena, Tuéjar, Vallada and Cortes de Pallás. ture, which means considerable saving in the cost of All the information we found made it possible to fuel, sometimes not very abundant in many areas. draw up a map to show the possible historic quar- Besides, after grinding and sieving it, it can be used ries in the province (fig. 5). immediately, and it is even recommendable to do Finally, according to all the data analysed in so, as it is not necessary to wait for it to cool, as it the province of Valencia, we can conclude that the is in the case of lime, which prolongs its production operation of the quarries was in the open air, and time and makes its production more expensive. only the one in Alfarp in the Cerro de las Cuevas The calcinations process of gypsum changed in was underground, according to the 1928 mining the 18th century thanks to the scientific advances statistics. Furthermore, it shows that crude gyp- that favoured uninterrupted research into gypsum, sum was used for construction, for making and which furthermore coincided with the industri- obtaining refined gypsum, for masonry and cobble alisation process of the materials, thanks to the stones (SA 1925). introduction of different types of kilns to procure a rational calcination process. However, in most Spanish rural areas traditional kilns were still used, 3.2 Traditional gypsum production so the two sorts of gypsum were still produced Historically, for the traditional production of gyp- until very recently (Villanueva 2004). sum they simply excavated the quarries or used artisanal kilns, very similar to lime kilns, also 3.3 Qualities & peculiarities of traditional known as Moorish kilns, located in the vicinity of gypsum the mines or at the building sites. The extraction of rock gypsum is very easy, since it is not very hard In general, gypsum is a versatile, light material and does not require important technical methods (three time lighter than concrete), breathable, that would involve extra cost. resistant, with great plasticity, fast-setting and The traditional kiln was a simple cylindrical with low conductivity, so it is very suitable for use masonry construction of dry stone, of variable as thermal insulation. But it also has relatively low height and with an opening at the front, usually built hardness and is very sensitive to water, so that it into a slope. It was filled with rocks of gypsum, ini- is a very hygroscopic material, and therefore direct tially forming a corbelling dome for the hearth with contact with the ground or water must be avoided. larger ones (fig. 6, Mileto & Vegas 2008). Nevertheless, there are great differences between

415 traditional gypsum and industrial gypsum that with many applications and properties. It would influence their behaviour to weathering. Industrial- mean rescuing a construction material with a ised gypsum is more and more pure and homoge- very different composition from current industrial neous due to the prior selection of the raw material products, but which has withstood the passage of and uniform firing, and it is characterised by being time and in many cases also abandonment with a single—or dual-phase and less porous, with less great deal of resistance and dignity, as we can see mechanical resistance, worse adherence and less in the traditional constructions in the province of elasticity in comparison with artisanal gypsum Valencia. Besides, it would also involve retrieving made with different phases (Sanz 2009). So a well- constructive techniques that have unfortunately executed historic outer rendering with traditional fallen into oblivion, but which are a mark of iden- gypsum, that is, with smooth, well-compacted tity of local constructions. Finally and above all, surfaces, resists the impact and damp of rainfall the traditional use of gypsum would involve apply- very well, which favours partial hydration of the ing sustainable, ecological, environment-friendly anhydrous phases it contains, thus avoiding poros- criteria, both in restorations and in new construc- ity and increasing the mechanical resistance of the tions and rescuing the constructive wisdom of our rendering (Sanz 2009). ancestors to enhance architecture and the quality of life of those who occupy it.

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