Abstract A series of experimental studies are presented that simulate capillary flow of water in discrete cracks in cementitious materials. A number of amendments to existing capillary flow theory are adopted which take the form of correction parameters for stick–slip behaviour of the meniscus, frictional dissipation at the meniscus wall boundary and slip between the fluid and solid wall. A benchmark study to examine capillary flow in small diameter glass capillaries is reported and this provides data to validate the amended theoretical model. Predictions made using the amended model closely match the experimental results of capillary rise in discrete cracks in cementitious materials allowing the correction parameters for capillary flow in planar cracks to be determined. Finally, capillary rise in a discrete natural crack of known aperture is considered and a relationship is proposed which predicts the capillary rise response in a natural crack in terms of an equivalent planar crack.