Compatibility Assessment in the Replacement of Damaged Sandstone Used in the Cathedral of Huesca (Spain)

In order to manage problems arising from rainwater/rock interaction in Miocene sandstones (calcareous litharenites) widely used in various monuments of the Ebro Valley (NE of Spain), a survey has been conducted with particular application to the building and architectural decorative materials of the Cathedral of Huesca. Once the current state of decay was diagnosed and the processes of alteration (enhanced by certain intrinsic factors and their particular exposure to the environmental conditions) were detected, a pre-restoration experimental assay was conducted. On the one hand, to propose the best stone replacement, this study evaluates the compatibility of the available sandstones in the local market based on their intrinsic features, especially those related to hydric behaviour. Once the most suitable sandstone was selected, pore size distributions were determined along with accelerated ageing cycles to show the importance of selecting properly the potential replacement sandstone. In a second step, to determine the effectiveness and long-term efficacy of four water-repellent products, several on-site and laboratory tests were performed. From the experimental results obtained, remedial works have been proposed which will be useful not only for the restoration programme of this monument, but also for other emblematic architectural Heritage in the Ebro Valley.