Nondestructive testing of plastered mosaics with the use of active thermography approaches

Abstract

ABSTRACT In this work, different mosaics covered with various plaste rs (of thickness and compositions) were evaluated in lab by means of active long wave and mid wave thermography approaches, with the intention of detecting the tesserae beneath the plastered surface. Thermal images as well as thermal contrast curves between plastered surfaces and plastered mosaics were recorded. Special considerations concerning the applicability and accuracy of the used approaches for this specific application are presented. Results from the assessment are presented and discussed, indicating that images seeing through the mortar–plast er on plastered mosaic surfaces can be obta ined using active thermography approaches. Keywords: Thermography, non - destructive testing, plastered mosaics, detection 1. INTRODUCTION During their lifetime the different historic structural complexes have subjected to various conservation and restoration interventions. In a large number of cases such interventions have led to the covering of materials of great historical value and significance, as in the case of mosaics. With a view to the strict conservation regulations concerning historical sites and in particular mosaics, where sampling for destructive testing and investigation is prohibited, the development and use of Non- Destructive Testing and Evaluation (NDT&E) techniques is considered to be essential. NDT&E techniques such as infrared thermography have been widely used on a number of occasions in the cu ltural heritage protection area, and have been proved to provide substantial information rega rding the investigation and evaluation of historic materials and structures. There is a vast amount of research works in the literature concerning the application of IR thermography for the characterization of building materials [1], the inspection of historic buildings [2] and moisture monitoring and assessment in ancient buildings [3], the diagnosis of surface and near-surface defects [4] as well as subsurface defects [5], the subsurface investigation of materi als [6], the assessment of conservation interventions and materials in historic structures [7], the detection of subsurface layers [8], through various active approaches. In this work different plastered mosaic surfaces were investigated in the laboratory with the use of Cooling-down Thermography (CDT), Pulse Phase Thermography (PPT) an d Thermographic Signal Reconstruction (TSR) techniques, in order to identify their sub surfaces – reveal of mosaics.