The integration of non destructive techniques and methods to assess the conservation conditions of painted plaster

The work presents the results of an in-situ experience performed using combined non-destructive testing techniques to support the restoration plan for the vaults of a Neoclassical church in Turin. During the restoration work at the Church of San Massimo, it was necessary to evaluate the areas of plaster which had become detached from the spandrels of the dome’s frescoed surfaces. The investigations were carried out with the complementary use of qualitative and quantitative infrared thermography with remote visual inspection. First of all, we evaluated the heating system best suited to the geometry of the object and its colour finish using IR qualitative thermography, than we carried out a thermographic analysis in active conditions (QIRT) with the application of an experimental procedure. The Thermal Inertia study of a number of sample zones chosen on the surface and compared with a reference area (sound area according to the knocking-test) enabled us to recognize deteriorated areas without contact with the paintings. The comparison of these results to the outcome of the qualitative IR testing allowed us to extend the indications obtained from the examination of individual areas to entire regions without, however, gaining information on the type of plaster detachment. The results obtained from the IR investigations enabled us to focus the visual inspections on the deteriorated areas. The indirect visual analysis was carried out within existing cavities made in the past to inject consolidation material, cracks in the wall and small holes made specifically. The combined use of the two techniques allowed the assessment of the state of deterioration in the detached areas and also allowed us to highlight areas requiring urgent conservation actions.