Thin spray-on liners (TSLs) are relatively thin (2-5 mm) fast setting liner materials that are sprayed onto rock surfaces to support mining excavations. The adhesive strength between a TSL and a rock surface is an important property controlling the design and performance of TSL rock support systems. In this study, direct pull-off TSL adhesion tests were interpreted based on a fracture mechanics approach. An edge crack propagation equation for a generic case (nu not equal 0.5) was derived and the failure modes of TSLs were studied. It was found that the current TSL adhesion test sample geometries show confined behaviour, the failure mode of the tests are edge crack propagation. Bulk cavitation of TSLs can only occur for very compliant samples (E < 0.6 MPa). Adhesion tests done on a TSL product, Tekflex, applied on concrete substrates were examined to verify the edge crack propagation. (c) 2012 Elsevier Ltd. All rights reserved.