The performance of shear-compression stone masonry walls with regard to their interaction with plaster is investigated by means of numerical simulations. A 3D finite element model based on the simplified micro-modelling technique is developed for the masonry-plaster system and verified against test results. The walls are simulated by using the commercial finite element software Abaqus. A constitutive law specifically formulated for brittle materials is used for the stone blocks and a material model taking into account the evolution of their properties under cyclic loading is used for the mortar joints. The model is the extension of a model previously developed for unreinforced mortar-brick masonry walls. In its extension to stone masonry, a modelling technique is introduced in order to capture the interaction between the masonry wall and the plaster. In the comparison with the test results the model shows itself capable of capturing two main phenomena that govern the masonry-plaster system: i) the cracking of the plaster and ii) its detachment from the masonry wall.