Evaluation of Electromigration Desalination of Granite Contaminated with Salts–A Contribution to the Conservation of Architectural Surfaces

Abstract

Different cleaning technologies have been available for cleaning monumental façades, of stone or mortar. This is not only necessary for aesthetic reasons, but for the removal of salts that promotes conservation, as surface erosion may affect the long term preservation of buildings. The main advantage of eletromigration treatment is its efficacy in the salts removal or reduction in very porous materials, without damaging the original material. Many monuments of North of Portugal have granitic masonry and stonework structures that, sometime, as a result of continuous exposure to the rainwater infiltrations, or in the case of buildings near maritime cost, due to the marine-aerosols influence, salt efflorescence and disaggregation occurs. Hence, it is important to proceed in removal of chloride salts from the contaminated granite walls. This research work deals with electromigration desalination of contaminated “Mondim Yellow Granite” samples, presenting the physical properties, mineral composition, porosity and internal structure. This type of granite was selected because is frequently used in traditional buildings and monuments of the North of Portugal. The aim of the research was to evaluate the desalination effectiveness of electromigration. By its application chloride salts were completely removed and sulfate ions reduction was significant. Differences in effectiveness of the desalination were analyzed and are attributed to the shape of granite specimens. Results obtained demonstrate the viability of application of this electro kinetic procedure for removal of chloride and sulfate ions of granite ashlars of the monuments.