This paper intends to evaluate the short- and long-term effects of high-range water-reducing (PCE and PNS) and viscosity-modifying (potato starch) admixtures when used alone or together in the formulation of lime mortars. Results showed that PCE and PNS led to a moderate decrease in porosity, a slower and lower water intake and a significant improvement in mechanical strength, both in the short- and long-term. However, they were also responsible for a delayed carbonation and an increased stiffness, and PNS, in particular, for a slower drying and lower water vapour permeability. Still, most changes were below those induced by the use of cement in blended lime mortars. In turn, potato starch led to an increase in porosity and pore size, to a faster carbonation and was not detrimental to mechanical strength. It presented a dominant effect when used together with PCE due to the higher dosage added. Nevertheless, the combined use of these two admixtures proved to minimize some of the disadvantages associated with their individual utilization in lime mortars.