Comparative analysis of cement-based and historic gypsum-based mortars for historical Restoration: Implications on mechanical and thermal compatibility

The restoration of historic building façades presents challenges worldwide, especially in terms of maintaining the structural integrity and thermal performance of the original materials. This study aims to evaluate the compatibility of different mortar types used in historical restoration, specifically comparing gypsum-based and cement-based mortars. To achieve this, a comprehensive experimental approach is employed, integrating chemical (SEM, XRD, TGA, and FT-IR), mechanical, and thermal analyses. The study presents a comparative analysis of gypsum-based mortar used in 200-year-old historic Cas houses in Siirt (Southeast of Türkiye) and cement-based mortars used in restoration and conservation applications. Findings indicate that gypsum-based mortars exhibit superior compatibility with historic masonry structures due to their porous and flexible nature, reducing structural stress and improving thermal balance. Conversely, cement-based mortars contribute to significant structural damage in historic masonry due to their rigid nature, leading to shear stress failures, particularly in seismic regions. This research provides novel insights into the role of material selection in heritage conservation, emphasizing that cement-based mortars may not be suitable for historic restorations due to their mechanical and chemical incompatibilities. Instead, the study highlights the importance of using traditional materials, such as gypsum-based mortars, to maintain the long-term durability and authenticity of historic structures.