To enhance the thermal durability and at the same time to achieve the sustainability in this paper, a novel approach of using fly ash based geopolymer mortar had been introduced to protect the steel wire mesh layer present in the ferrocement panels. Parametric study was done to study the influence of role of wire mesh, volume fraction from 0.8% to 1.96%, changes in temperature of heating and the application of geopolymer mortar on the ferrocement to analyse their effect on the post fire mechanical properties such as load-deflection behaviour, stress–strain behaviour, percentage of strength retained, moment of resistance and Young’s modulus. Although the cement mortar showed higher retained strength upto 600 °C, the geopolymer had the maximum retained strength after 900 °C due to the gradual improvement of geopolymerisation process. The retained strength ranged between 46.3–99.1% and 34.91–88.78% for the ferrocement panels with geopolymer and cement mortar respectively. Ferrocement panel with geopolymer mortar showed 12.9% improvement in the post fire flexural strength at 900 °C for the volume fraction of 1.8% as the geopolymer mortar possessed double the times enhanced retained compressive strength of cement mortar after fire exposure.