Correlating visual grading with NTD methods for assessing timber condition in historic buildings

This study aimed to develop, apply and assess a visual grading system that could evaluate the state of preservation of historic buildings' structural timbers and correlate it with three NDT methods that are widely used during diagnostic surveys. Assessing timber condition is crucial not only for the structural analysis of buildings, but also for reinsuring that well preserved original material of Cultural Heritage will not be lost. However, assessment based only on NDT results may be biased as it depends on many parameters such as i) the natural variability of wood ii) the type and degree of deterioration iii) the experimental conditions etc. Furthermore, results obtained are not always coinciding and often they are not correlated to the macroscopic condition of timbers. Therefore, this work based on international standards, developed a visual grading system and correlated it with results obtained from ultrasounds application, resistograph profiling and X-ray radiation. All three NDT techniques were tested on samples coming from a post Byzantine mansion in Athens that presented various types and degrees of decay. The results obtained indicated that the developed visual grading system can successfully assess the preservation condition of timbers as it showed a positive correlation with all NDT techniques deployed. It is recommended however, timbers graded as moderately attacked, to be additionally assessed by an NTD technique.