Characterization of the old rendering mortar of a Brazilian historical building

This paper studies the constitution and properties of lime-based mortars, collected in the Casa Amarela (Yellow House), a building of the end of the 19th century, located in Belo Horizonte (Brazil), object of this case study. An experimental study was developed to characterize the rendering mortar of this historic building, aiming to support future interventions/propositions of a recovery mortar compatible in physical, chemical and mechanical terms with the original mortar. The results of the investigation of this material are presented through its microstructural (scanning electron microscopy + energy dispersive spectroscopy and stereoscopic optical microscope), chemical and mineralogical (X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and infrared spectrometry thermogravimetric) characterization. The detected phases were: quartz (SiO2); calcite (CaCO3) and microcline (KAlSi3O8). With the images obtained with SEM, it was possible to select microregions to target the EDS microanalyzer and perform semiquantitative chemical analysis. The microstructural and mineralogical characterization of the old mortar provided relevant data regard its composition, as well as its properties in the hardened state, which is closely related to the durability of the system. The results indicated a lime-based mortar without the presence of Portland cement or additions of organic materials.