Environmental risks assessment and preventive conservation strategy for the Portico de la Gloria, Santiago de Compostela Cathedral

In the framework of the Santiago de Compostela Cathedral Program a multidisciplinary investigation of the Portico de la Gloria was carried out between 2009 and 2011 to identify the main environmental risks and to develop a preventive conservation plan to be integrated in the general management strategy of the Cathedral. This study included historic and archivist research, structural studies, mineralogical analyses, biological sampling, cleaning tests, microclimatic monitoring. The main weathering factors and the related damage processes were identified. Results have shown that the main responsible for the observed damage was the infiltration of rainwater through the roof, due to cracks in the structure of the Cathedral. Other environmental factors having a remarkable impact on the state of conservation of the polychrome and its substrate were the solar radiation, the thermo-hygrometric cycles, the particle deposition and the biological growth. Solutions were suggested to improve the environmental conditions, thus reducing further damage.