Greywacke rock masses are the most prominent bedrock type across New Zealand, forming approximately 20 % of the country. This paper reviews the publicly available laboratory testing data on the geomechanical properties of greywacke from the Wellington region and compares the results with two recent studies. This includes compilations of density, unconfined compressive strengths, tensile strengths, Poisson’s ratio, Young’s Modulus, and mi factor. This paper also presents the first published geomechanical data from a cataclasite zone in the greywacke of the Wellington region. The overall results presented in this paper highlight the influence of both weathering and discontinuities on the geomechanical properties derived from the testing of core samples. The results are discussed in the context of sampling bias, scale effects and recent developments in the geomechanical characterisation of discontinuous rock. Two different approaches for characterising the rock mass geomechanical properties of greywacke at the project-scale are presented. The first approach uses the GSI as the main parameter to capture the change in rock mass character with depth while the UCS remains constant. The second approach uses the UCS as the main parameter to capture the change in rock mass character with depth while the GSI value remains constant.