Identifying Anomalies Underneath Traditional and Reinforced Plasters Using IR Thermography on Masonry Laboratory Specimens

Non-destructive diagnostic investigation is a fundamental tool for identifying the in-situ condition of historic materials and for guiding, along with other information gathered about the building, the choice of appropriate conservation actions. In this regard, infrared (IR) thermography is a widely used survey technique in historic buildings, particularly useful in the presence of valuable coatings (e.g., plasterwork or frescoes). Radiometric imaging provides information on construction techniques and any anomalies present in the surface layers due to inhomogeneities, historical traces, moisture, detachments, etc. The aim is to present the results of a comparative study carried out by two research units (UR, University of Padova and Politecnico di Milano) on two full-scale masonry specimens, simulating the localised presence of anomalies and adhesion defects at the plaster-masonry interface. The panels reproduce two multi-leaf masonry, with outer faces made of rubble stone or regular clay brick. The former is covered with a lime-based plaster reinforced with a BTRM (Basalt Textile Reinforced Mortars) mesh, the latter with a cementitious one including a steel net, in both cases at one side. Artificial anomalies were reproduced at the plaster-masonry interface, as Teflon strips of various sizes simulating air pockets, elements of various materials (steel, wood) embedded at the masonry surface, to simulate inclusions and discontinuities, and sponges soaked of water to simulate the presence of moisture. The wall was investigated independently by the two URs by means of IR thermography under both ambient (solar radiation) and active (artificial heating) conditions. The results showed the different potential of the systems adopted by the URs in identifying the imposed defects, depending on the type and duration of the induced heating and the type and thickness of plaster.