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

• XV-XVIIIth century plasters were studied to reproduce them at the laboratory scale.
• Another goal was to give to restorers practical methods to perform restoration works.
• Different approaches and technologies, innovative or linked to local traditions, should be used.
• A multidisciplinary approach was activated between Architects and Materials Scientists.

In this paper, the systematic physical-chemical characterisation 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 to XVIIIth centuries) are in a quite good state of conservation despite the prolonged exposition to weathering agents. This behaviour 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 characterisation realised 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.