Mónica Álvarez de Buergo

Evolution in the use of natural building stone in Madrid, Spain

Many types of stone have been used for construction in Madrid. In historical times, their use was determined by the proximity of the geological resources, the ease of quarrying and transportation links to the city. More recently, as transport connections and quarrying techniques have improved, quality and durability have become key determinants of building stone selection. Local flint was used intensively from the ninth to the eleventh century, when it was replaced by Redueña dolostone, used in turn until the seventeenth century. Granitic rocks from the Guadarrama Mountain Range that crop out in the northern and western area of the province increasingly began to be used in the city from the sixteenth century. Traditionally known as Berroqueña stone, this building stone was quarried in a number of areas; the primary point of supply was Zarzalejo, and from the eighteenth century the granite used was mainly quarried in the Alpedrete area. Eighteenth century advances in underground quarrying made it possible to extract a limestone (Colmenar stone) located in the southeastern part of the region. Together with Berroqueña stone, this limestone became one of Madrid’s traditional building stones, and both, highly esteemed for their excellent petrophysical properties and durability, are still used today.

Soluble salt minerals from pigeon droppings as potential contributors to the decay of stone based Cultural Heritage

This paper describes the salt content and pH evolution in solutions produced by the water-soluble extraction of accumulated pigeon droppings. Results demonstrate that these accumulations contain 4 % of soluble salts. Therefore, they are a plausible source of salts commonly found on buildings. These salts comprise halite, sylvite, potassium calcium sulphate, aphthitalite, apatite group minerals, weddellite and gypsum. The interaction of solutions formed from pigeon droppings with porous limestone was also studied. A noticeable deterioration in limestone due to acid attack was observed, including surface etching of rock-forming minerals.

The measurement of surface roughness to determine the suitability of different methods for stone cleaning

The roughness of stone surface was measured, before and after bead blasting-based cleaning methods, to select the most efficient one to be used in masonry and stonework of specific areas of the Cathedral of Segovia (Spain). These types of cleaning methods can, besides the removal of soiling and surface deposits, leave a rougher surface, which would mean higher and more rapid water retention and deposit accumulation due to a specific surface increase, therefore accelerating stone decay. Or, in contrast, the cleaning method can be so aggressive that it can smooth the surface by reducing its roughness, a fact that usually corresponds to excessive material removal—soot and deposits–-but also part of the stone substrate. Roughness results were complemented with scanning electron microscopy observations and analyses and colour measurements. Finally, it was possible to select the best cleaning method among the six that were analysed, for different areas and different stone materials. Therefore, this study confirms the measurement of surface roughness as a reliable test to determine the suitability of stone cleaning methods; it is a non-destructive technique, portable and friendly to use, which can help us to rapidly assess—together with other techniques—the efficacy and aggressiveness of the stone cleaning method.

An urban geomonumental route focusing on the petrological and decay features of traditional building stones used in Madrid, Spain

The stone traditionally used to build cities contributes to their personality and attests to the geological substrate on which they stand. While stone decay in the built heritage can be attributed to a number of causes, anthropic activity has a particularly significant impact. The geomonumental routes project is one of the initiatives proposed in recent years for urban routes that convey geological fundamentals by observing the rocks present in heritage structures. Its innovative approach addresses traditional stone properties, original quarrying sites and mechanisms of decay. Madrid’s Royal Palace is a fine example of the use of traditional building stone in the centre of the Iberian Peninsula. In the geomonumental route proposed, the building doubles as an in situ laboratory that affords an overview of the main petrological properties of the two traditional stones most commonly used in the city’s built heritage, the forms of decay they are subject and the factors underlying such alterations. This route constitutes a tool for showing the main petrological features and decay forms in traditional building stones found in urban heritage façades, with a special focus on anthropic impact, primarily air pollution and the use of conservation treatments that time has proven to be unsuitable.

Assessment of Different Methods for Cleaning the Limestone Façades of the Former Workers Hospital of Madrid, Spain

Abstract Five different methods for cleaning the limestone façades on what was originally the Workers Hospital in Madrid are analyzed in this paper. Due to the pollution in the surrounding air, just 20 years after a prior cleaning operation, sulfate crusts had developed on the entire stone surface of the building. The gypsum mortar used in the original masonry constituted an additional source of sulfur. Limestone is a traditional building material in Madrid and its surroundings. The petrography, mineralogy and petrophysical properties of the biomicrite, pelmicrite and biopelmicrite varieties of limestone identified in the hospital walls were determined. Analysis of a black layer on the stone surface showed that it consisted primarily of sulfate crusts. The cleaning methods tested were alkaline gels (sodium hydroxide and potassium hydroxide), pressurized hot water, glass bead blasting and latex peeling. The criteria for assessing the effectiveness and potential risks of the various cleaning systems included changes in the chromatic parameters of the stone, the formation of alteration products (i.e. salts) and modification of the stone surface. The stones cleaned with the three most effective methods, together with a rain-washed stone as a reference, were washed with water to generate an artificial runoff. The collected drain water was analyzed to determine the presence of any by-products from the cleaning process. The method found to be most effective and which caused the least alteration to the stone surface was glass bead blasting, particularly after adjustment of the bead size and pressure conditions used for the test.

The Influence of Past Protective Treatments on the Deterioration of Historic Stone Façades A Case Study

Abstract During a 2002 cleaning operation on the Royal Palace (Madrid, Spain), some stains actually became much more visible after the limestone and granite stones were cleaned. These stains were analysed by several instrumental techniques (both in situ and in the laboratory) and were found to result from past protective treatments. Some of these treatments had formed thin, impermeable films that did not allow the water inside the ashlar to evaporate. Sub- and crypto-efflorescences (gypsum, thenardite and nitratite) broke the protective film, generating efflorescences on the surface. The treatments had not penetrated the stone, and the stains were merely superficial. The method used for the cleaning of the stone façades (pressure water jet) was ineffective for the removal of these protective treatments, which at present are deteriorating the stone on which they were applied.

The behaviour of consolidated Neapolitan yellow Tuff against salt weathering

Salt crystallization is a strong weathering agent in porous building materials. The crystallization pressure exerted by salt crystals, growing in confined pores, is found to be one of the main causes for damage. This paper presents the results of laboratory experimentation carried out on the Neapolitan Tuff, a pyroclastic rock largely used in Campanian architecture. Several specimens, collected from a historical quarry near the city of Naples, were treated with two different consolidating products: a suspension of nanosilica in water (Syton X30®) and ethyl silicate (Estel 1000®) dispersed in organic solvent (TEOS). Untreated and treated samples were then artificially degraded using salt crystallization tests in order to assess the effectiveness of consolidation treatments. A systematic approach, including mercury intrusion porosimetry, peeling tests and point load test, was employed to evaluate the correlation between the salt crystallization and the micro-structural features of the tuff. In addition, in order to make a correlation between porous structure of materials and susceptivity to salt crystallization, the calculation of the crystallization pressures was performed. In all samples, at the early stage of crystallization, the presence of gypsum was revealed, coming from the precipitation of sulphate ions, introduced during the test, and sodium ions, coming from the zeolites within the stone. Results showed that both consolidants increase the resistance of tuff to salt crystallization, although they induce an increase in crystallization pressure. Ethyl silicate, however, shows a better behaviour in terms of superficial cohesion, even after several degradation cycles.

Evaluation of Portable Raman for the Characterization of Salt Efflorescences at Petra, Jordan

ABSTRACT The advantages of using portable Raman spectrometer equipment, such as avoiding sampling and providing a higher number of results, are contrasted with some of its shortfalls that make other analytical techniques necessary to characterize salt efflorescences on historic buildings. In-situ analyses of salt efflorescences were carried out with a portable Raman at both the so-called “Silk Tomb” and “Monastery” rock-cut façades at the Archaeological Park of Petra (Jordan). Samples were also taken to be analyzed in the laboratory with X-ray diffraction (XRD) and Environmental Scanning Electron Microscope with Energy-Dispersive X-ray spectroscopy and Cathodoluminescence (ESEM-EDS-CL). This research shows the pros and cons of these analytical techniques—and how they complement each other—to identify the occurrence and determine the origin of soluble salts, which are deeply damaging these rock-cut monuments by salt crystallization processes.

Characterization of concrete from Roman buildings for public spectacles in Emerita Augusta (Mérida, Spain)

The aim of this work is to characterize the original concrete from Roman buildings for public spectacles, theatre and amphitheatre, from Emerita Augusta, Mérida, Spain. An advanced knowledge of the Roman concrete composition is required for a reliable restoration and preservation of these ancient monuments. The concrete was studied through mineralogical (optical polarized microscopy and X-ray diffraction) and petrophysical (bulk and real density, open porosity to water and Hg, mechanical strength and ultrasonic velocity) analyses. With this work, it is possible to fill the gap that exists in this field and the characterization of the materials used in the Roman concrete from these two buildings, never previously studied, despite the significance of this archaeological ensemble, declared a World Heritage Site by UNESCO in 1993. The results allowed us to determine the composition of the Roman concrete and to infer the provenance of the aggregates used in these monuments.

The Use of Portable Raman Spectroscopy to Identify Conservation Treatments Applied to Heritage Stone

ABSTRACT Nondestructive in situ analysis of materials is highly desirable in cultural heritage studies, because it precludes the need for intensive sampling. The present study focused on the usability of Raman spectrometers, which can provide such analysis, in the identification of conservation treatments applied to stone materials forming part of the architectural heritage. Two products commonly used to conserve stone monuments, an ethylmethacrylate copolymer and an ethyl orthosilicate, were analyzed with a Raman spectrometer, both as supplied and after application to limestone. The main conclusion was that portable Raman analyzers can detect the presence and—in some cases—identify the nature of products on stone substrates. The latter is not always possible due to product-stone substrate interaction. The study clearly showed that a product and substrate database is needed for portable Raman spectroscopy to be usable in the analysis of conservation products, both before and after application to stone substrates.