Slurry erosion tests were performed on various types of repairing mortars in order to determine the factors influencing the abrasion-erosion resistance of some mortars. An in-house built apparatus was used, which produced a slurry jet that impinged the surface of mortar specimens with an incidence angle of 45° and a velocity of 18.5 m/s. The results showed that the epoxy mortars were the most erosion resistant compared with cementitious grouts and polymer-modified cement-based mortars. The erosion of mortars is controlled by the wear of the binder (epoxy or cement paste), and a strong relation exists between the erosion resistance of the mortar and the absence of microporosity in the binder. The results also suggest that to minimize the exposed areas of the binder, well-graded, i.e., small- and large-size, sand particles should be used.Key words: abrasion, erosion, repair mortars, cementitious grouts, polymer-modified cement-based mortars, epoxy mortars, hydraulic structures.