Evaluation of non-destructive techniques for mechanical characterisation of earth-based mortars in masonry joints

•Non-destructive tests are used to characterise earthen mortars in masonry joints.•Durability and mechanical properties of earth-based mortars are assessed on-site.•Penetrometer, Schmidt hammer, pendulum hammer and scratch tests are evaluated.•Reliability and limitations of NDTs for characterising earth-based mortars are identified.•Six qualitative indicators to compare the performance and feasibility of NDTs are defined.