The contribution aims to present the path of knowledge on the external surfaces of the Courtyard of the Cavallerizza and the Castle of San Giorgio in Palazzo Ducale in Mantua, the subject of an upcoming conservation project. In particular, the results emerged through the autopsy and stratigraphic survey of areas selected by sample, relating to the technique of execution and the constituent materials of the finishes. From this survey, the characteristics of the original structure have been defined so as to have a clear relationship with respect to integration or degradation. At the same time, following specific evidence and to support the cognitive operations carried out in situ, in-depth diagnostic investigations were carried out in order to support and clarify the contents detected previously by interpreting the scientific data on the nature of the materials and the degradation present. The re-elaboration and critical analysis of the data acquired through various in-depth techniques, as well as providing indications for intervening on the causes of degradation, has supported the designers in the development of intervention methods and in the choice of the most suitable materials for conservation, based on the state of conservation of the nearby areas and the interfaces with the substrate. The scientific data have been compared with the historiographic information in order to have an objective comparison.