The plasters of the Sacro Monte of Varallo Sesia. From the characterization to the proposition of a restorative mix

In this paper, the systematic physical-chemical characterization of historical plasters of the Sacro Monte of Varallo Sesia, Italy, the study of the local constructive techniques, as well as the evaluation of new restoration plasters is presented. The selected samples (from XVI–XVIIIth centuries) are in a quite good state of conservation despite the prolonged exposition to weathering agents. This behavior is due to the good manufacturing and to the peculiar smooth finishing layers which reduce water permeability and allow water drops to slide off. The plasters characterization realized in laboratory for in-situ integration is also presented. These plasters should meet functional and aesthetical requirements and must satisfy the compatibility issues not only related to the physical-chemical aspects.