This work presents the diagnosis procedure followed to determine the degree of damage of a 100-year-oldreinforced concrete building located in Barcelona city, the Sant-Manuel pavilion at Hôpital de la Santa Creui Sant-Pau. Some structural components of this building were affected by severe corrosion problems inthe reinforcing steel UPN profiles. In order to obtain a representative sample set, a preliminary inspectionof the macroscopic architectonic structure was applied at selected zones that exhibited the metallic back-bone. Gravimetric and electrochemical techniques have demonstrated that some UPN profiles presentedhigh corrosion rate. This was mainly due to the presence of water pipes installed beside the metallicstructure, which was a source of humidity, and also to the presence of calcium carbonate, calcium silicatehydrate, and calcium chloride substances inside the cement in direct contact with the metallic struc-tures, which were responsible for the steel depassivation. The work shows a practical example of howa suitable combination of chemical, physical and electrochemical techniques can be applied together tocharacterize a corrosion process, the obtained results validating and corroborating the prediction of thecorrosion rate in metallic structures.