The effects of mixing procedure, testing procedure and relative proportions of constituent materials on the rheology of fresh mortar, as measured by the ViscoCorder, have been studied. Mortar shows structural breakdown, and the flow curve of the broken down material conforms to the Bingham model. The yield value and plastic viscosity vary with composition in a similar way to that shown by fresh concrete: tests with the instrument on model concrete (i.e. with no coarse aggregate) could be useful in predicting the behaviour of fresh concrete.