The use of drilling test to investigate the salt distribution in air lime mortars

One of the principal causes of deterioration in historic buildings is the presence of salts. Porous and low-strength materials, such as soft mortars, are particularly susceptible to the deteriorating action of salts. The most severe damage occurs when salts accumulate behind the material surface, causing crumbling, exfoliation, and spalling. For this reason, the use of minimally invasive techniques to locate the presence of salts below the surface can be helpful to make an informed decision on the best practice for conservation strategies. In this work, the effectiveness of the drilling test in investigating the sub-surface distribution of salts in two lime-based mortars was evaluated. The technique proved to be effective as the increase in the recorded drilling forces was well correlated with the salt content measured within the materials. In particular, the drilling test results showed a similar behavior between the two mortar mixes. This finding was confirmed by the ultrasonic pulse velocity tests, visual observations, and weight loss measurements performed after the salt aging test. Another aspect of the work is the contribution to the processing of drilling profiles in salt weathered soft mortars. Indeed, the results of drilling tests in soft mortars are very scattered due to the intrinsic heterogeneity of these materials. Thus, the proposed processing of drilling data was effective in evidencing the effects of salts, by reducing the influence of the chip formation on the drilling profiles.