Lime mortar is one of the most ancient and common building materials used by man for centuries, all over the world. Unfortunately, over the last two hundred years, lime has been progressively replaced by Portland cement, which has been used indiscriminately in the majority of deteriorated historic buildings. Because of the highly regrettable, irreparable damage caused by these wrong repair interventions, nowadays restorers and manufacturers have understood the importance of recovering lime to design traditional, sustainable, compatible and durable repair mortars. Notwithstanding, the industrial production of mortars has led to differences in the manufacturing techniques involved and the characteristics of the components used, with the consequence that ready-to-use (industrial) mortars do not show the same quality as traditionally prepared mortar.The overall aim of this research project is to design a suitable and durable ready-to-use lime mortar that can be used as repair material in historic buildings. To improve the quality of the mortar designed, we will use natural admixtures (i.e. derivatives of the vegetable and animal world) to modify some characteristics of mortar. The interest of studying and using these admixtures is clearly linked with the need of adopting sustainable industrial processes, which entail reduced pollution and energy consumption. This research will focus especially on the study of the durability of mortars prepared with such admixtures, towards different climatic conditions, pollution and microbiological activity. This study will be carried out by using chemical, mineralogical, petrographical techniques, as well as physical-mechanical and durability assays (accelerated and natural weathering tests). This research is innovative in the field of both restoration and industry, because it aims to investigate the long-term effects that natural and sustainable admixtures have in mortars, essential aspect of a correct repair intervention.