Ultrasonic drilling for the characterisation of building stones and salt induced decay

Historic stone buildings can experience severe decay through salt induced weathering. Decay can be easily seen with the eye but can also occur below the surface. Characterising the changes in the material's structural properties induced by weathering is essential for the evaluation of durability of the stone and for the decision on the best conservation strategy to maintain built heritage. Minimally invasive, in situ tools are needed to establish the location and state of decay at the site. Here an ultrasonic drilling tool is introduced with a specially manufactured tip to monitor subsurface properties of sandstones. Different types of sandstones with varying compressive strength are tested and an artificially weathered sample is investigated. The tool tip wear and exerted force on the drilled samples are evaluated and compared to conventional drilling. Ultrasonic drilling shows promising results for the use in conservation science to assess stone properties and decay.