A multi analytical approach to address a sustainable conservation of the main marble portal of the Monreal Cathedral

The Main Portal of the Cathedral of Monreale is one of its magnificent external architectural elements. Recently, a conservation campaign was carried out for increasing its state of conservation, endangered by physical decays phenomena. The previous restorations, occurred over time, and the rising damp have contributed to its worsening. An integrated and multi-analytical diagnostic campaign has been provided to investigate the constitutive materials, the decays and the restorations coverings. Thanks to the analytical results, it was set a sustainable conservation treatment aimed to remove the causes of decays in view of the retractability of the original matter in the future. A difficult and complex cleaning was performed to remove the old coverings and safeguard traces of the original polychromy. An inorganic-mineral consolidating treatment, ammonium phosphate based, was carried out to re-give cohesion to the powdered marble especially in presence of water and salts. Several strategies of application were provided to have an efficient consolidation. A so representative monument, as the main portal, required a sustainable approach, able to interfere with the future conservation.