Abstract This study gives an example of the steps that a repair work must include to be successful. It deals with a specific building, repair material (lime mortar) and application (render), but also with the study of the repair mortar in the laboratory and on site. Firstly, the original materials of the wall were characterized to ensure compatibility with the new repair mortars. Secondly, the suitability of different mortar mixes, made with lime and calcareous aggregate, was assessed by characterizing their properties after 15 months. At the same time, the repair mortars were applied in testing panels, and their behaviour under environmental conditions was studied and compared with that of the laboratory mortars. Mortar properties (shrinkage, adhesion, mineralogy, microstructure and texture) developed differently according to the curing conditions. The carbonation degree was higher in mortars cured on site (especially those with higher aggregate content), although in both cases it depended on mortar porosity. Testing the type of application on site was helpful to define the best performance of the designed mixes and to choose the most suitable one among them, which was found to be the 1:6 binder-to-sand ratio mortar applied in both layers of the render.