This work aims to improve the formulation of short flax fiber-reinforced mortar through coating the raw fibers with hydraulic binders like cement or lime, or cleaning them in boiling water prior to the coating. These treatments are chosen for their ability to reduce the water intake by the fibers and to minimize the migration of their extractible compounds toward the cement matrix. Formulations incorporating raw or treated fibers were characterized in the fresh state. The results showed a drastic reduction of water intake, which correlates with an improvement of the properties of the fiber-mortar mixtures in the fresh state, particularly in terms of the heat of hydration, initial setting time and consistency. Mechanical behavior of the different formulations is also evaluated by flexural tests.