Stone masonry buildings are vulnerable to a wide range of loadings, such as differential settlements and earthquakes. Damage to these buildings manifests itself mainly through cracks in the masonry walls, which often propagate along the interface between mortar and stone. In this study we investigate the role of the stone surface roughness on the interface shear strength, which is described through the Mohr – Coulomb failure criterion. To do so, we subject samples consisting of two units and one mortar joint to direct shear loading and a constant normal load. For the stone unit we used as proxy high-strength concrete that was cast against 3D printed surfaces with artificial surface roughness based on sinusoidal waves and vary the wavelength and the amplitude of these waves. We conducted 85 tests and analysed the influence of the wavelengths and amplitudes that characterise the surface roughness on the shear behaviour. We propose simple Mohr-Coulomb-based equations incorporating additional surface parameters. Based on which we can confirm that see that increasing surface roughness enhances peak, residual friction coefficients and cohesion.