In the rehabilitation and preservation of historic buildings, the coating mortar plays a fundamental role, it is the first element to show signs of degradation due to its function of protecting the substrate and exposure to deteriorating agents. Thus, in order to carry out a correct intervention it is essential to have knowledge about the historical building with regard to its cultural legacy, the construction techniques, the materials used and its characteristics, the constitution of the coating layers, as well as the elements of degradation gift. The need for preventive interventions in historic buildings makes this work investigative and scientific. The understanding of the original materials and the use of new compatible materials for restoration is a crucial point for a good intervention to be made and not to accelerate the degradation of historic buildings. Therefore, the present work aimed to characterize the mortar lining of a building located in Laginhas, Municipality of Caicó in Rio Grande do Norte; for this, on-site visits were made for visual studies, execution of floor plans, photographic records and collection of samples for laboratory tests; making it possible to perform the absorption test, visual, granulometric and chemical analyzes, in order to characterize the coating mortar. Based on the results, it was found that two lines 1: 7, in the other samples; the use of medium sand was also found to be the smallest aggregate used in the coating mortar.