Publication: Assessment of Different Methods for Cleaning the Limestone Façades of the Former Workers Hospital of Madrid, Spain
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Publication Date
2011
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Taylor & Francis
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En este trabajo se evalúan cinco métodos para la limpieza de la piedra caliza empleada en la construcción del Antiguo Hospital de Maudes (Madrid). Debido fundamentalmente al entorno urbano contaminado en el que se localiza el inmueble, 20 años después de la limpieza integral acometida en las fachadas, sobre la superficie de la caliza se han desarrollado costras de sulfatación en la práctica totalidad de los paramentos. Los morteros de yeso originales constituyen una importante fuente de azufre. La caliza estudiada es una piedra de construcción tradicionalmente empleada en la ciudad de Madrid y en sus alrededores. Se han determinado las propiedades petrográficas, mineralógicas y petrofísicas de las principales variedades de piedra caliza identificadas en las fachadas, biomicrita, pelmicrita y biopelmicrita. El análisis de las costras negras confirma que principalmente se corresponden con costras de sulfatación. Los sistemas de limpieza evaluados han sido dos geles alcalinos (hidróxido sódico e hidróxido potásico), agua caliente a presión, proyección de microesferas y aplicación de látex. Los criterios seguidos para evaluar la efectividad y el riesgo potencial de los métodos ensayados han sido la variación de los parámetros cromáticos en la piedra caliza, la formación de productos de alteración (fundamentalmente sales) y la modificación de la rugosidad superficial de la piedra. Las superficies pétreas ensayadas con los tres métodos que resultaron más efectivos, así como la superficie de la piedra lavada naturalmente por el agua de lluvia (tomada como referencia), han sido artificialmente lavadas. El agua del lixiviado recolectada ha sido analizada para determinar la presencia de posibles productos de alteración generados durante el proceso de limpieza. La proyección de microsesferas de vidrio, con el cuidado ajuste del tamaño de las partículas y de la presión de proyección, ha resultado el método más efectivo y el que menor alteración en la superficie de la piedra origina.
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.
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.