Earth masonry is a good alternative to more conventional materials in order to reduce the environmental impact of building materials. However earth construction techniques mostly rely on bricklayers’ experience, which is a hindrance to industrial development of this traditional know-how. This article proposes a methodology for the mix design of unstabilized earth bedding mortar based on mechanical criteria of the masonry and rheological criteria of fresh mortar. A test to characterize the shear strength of the masonry interface is specially investigated. The mechanical performances of the formulated mortar are then validated with laboratory scale characterization.