Choosing the Right Stone to Restore a UNESCO World Heritage City: Salamanca (Spain)

Abstract The city of Salamanca (Spain) was recognized as UNESCO Word Heritage City in 1988 because of the homogeneous historic architecture of the old downtown area. One objective of this status is to preserve the architectonic heritage. Consistency was achieved by using the locally quarried stones through centuries, mainly the Villamayor sandstone and an opal-cemented conglomerate, misleadingly named Salamanca Sandstone (Arenisca de Salamanca), and local granite. The city of Salamanca was built on top of the conglomerate, a Cretaceous–Tertiary lithic wacke, since the area was inhabited by the pre-Roman Vaccean tribe. After centuries, some of the most important buildings of Salamanca are deteriorating due to the water absorption and the increase of contamination in the city due, as parts were open to the traffic until recently, although at present only delivery vehicles are allowed. Restoration of these buildings should become a priority for the city, because UNESCO requires that the heritage is maintained or improved. Otherwise, the site would be delisted. Restoration may require replacement of the damaged parts and for this reason it is important to have a complete characterization of the stones used in the constructed heritage to determine suitability and the availability of rocks to be used in restoration. If the original stone had non- ideal properties, or it is not now easily available, an alternative appropriate stone should be selected carefully with the aim of maintaining the architectonic heritage. This paper deals mainly with the characterization of durability of the conglomerate as potential stone that can be used in the restoration of damaged buildings to inform the proper use as replacement when needed.