Identifying subsurface detachment defects by acoustic tracing

This paper presents a newly developed acoustic tracing method for a non-invasive survey of detachment defects of rendered masonry. The method analyses acoustic signals generated by tapping the surface in densely located points, which are registered together with the geometrical coordinates by means of a video camera. FFT analysis enabled a comparison to be made between the audible wall response and formalized parameters of the sound samples, i.e. the excitation band and the dominant frequency of the spectrum. It was concluded that the audible spectrum for non-detached parts includes several narrow band components, whilst the detached areas respond in a wider frequency band.