One technique for strengthening masonry infill walls against seismic lateral forces permitted by the Turkish Seismic Code is to add a plaster layer with mesh reinforcement to one face of the wall. The study described in this paper was performed to test and analyse the effectiveness of this technique for lateral loads. In the experimental study five specimens were constructed and tested under cyclic loads. Although the inclusion of the mesh-reinforced plaster layer increased the lateral strength and stiffness of the test specimen 44 and 127%, respectively, one specimen failed prematurely because of insufficient bonding of the dowel reinforcements that were used for transfer shear loads from the frame to the plaster. Direct anchoring of the mesh reinforcement to the reinforced concrete frame instead of using dowel reinforcements in the plaster layer provided a significant improvement in the lateral strength and behaviour of the test specimens. Two alternative layers of materials such as high-strength plaster and shotcrete for improving the strength were used instead of plaster. The most successful lateral performance was obtained from the specimen in which a mesh-reinforced high-strength plaster layer was used. The lateral load-carrying capacity and stiffness of this specimen were increased up to 150 and 250%, respectively.