The impact of fire on natural stone structures is a critical concern, particularly for historical buildings. This study examines the residual mechanical properties of sandstone after exposure to high temperatures. Cylindrical sandstone samples were heated to temperatures up to 900 °C and subsequently tested under uniaxial compression. The results indicate that mechanical degradation becomes significant beyond 460 °C, with compressive strength decreasing by up to 43% at 900 °C. Young’s modulus also declined substantially, while axial strain increased, indicating progressive structural weakening. Additionally, visible colour changes suggest mineralogical transformations. These findings provide essential insights into the fire-induced deterioration of sandstone, offering valuable guidance for the preservation and restoration of historical stone structures.

Marlstone, widely used in Romanesque and Gothic architecture across Central Europe, is a common component of heritage structures whose post-fire behavior is critical for preservation. This study examines fire-induced changes in marlstone to support post-fire assessment and conservation. Cylindrical specimens (35 mm diameter, 70 mm height) were heated to 620 °C, 870 °C, and 1100 °C, then subjected to uniaxial compression tests to determine residual strength, strain, and Young’s modulus compared with unheated controls. Both natural and quenched cooling regimes were evaluated. Complementary XRF and petrographic analyses identified mineralogical and microstructural changes, while CIELab color measurements quantified temperature-induced visual alterations. Results show temperature-dependent changes in mechanical performance, accompanied by transformations in silica and calcite phases, along with measurable color changes. Variability in response reflects the inherent heterogeneity and anisotropy of marlstone. These findings provide essential insight into the thermal vulnerability of historic marlstone masonry and offer practical guidance for conservation, restoration, and post-fire evaluation of heritage stone structures.

The impact of fire on natural stone structures is a critical concern, particularly for historical buildings. This study examines the residual mechanical properties of sandstone after exposure to high temperatures. Cylindrical sandstone samples were heated to temperatures up to 900 °C and subsequently tested under uniaxial compression. The results indicate that mechanical degradation becomes significant beyond 460 °C, with compressive strength decreasing by up to 43 % at 900 °C. Young’s modulus also declined substantially, while axial strain increased, indicating progressive structural weakening. Additionally, visible colour changes suggest mineralogical transformations. These findings provide essential insights into the fire-induced deterioration of sandstone, offering valuable guidance for the preservation and restoration of historical stone structures.