The role of physical properties of melts such as viscosity, diffusion, and surface/interfacial tensions in sintering and deformation mechanisms of ash deposits above glass-transformation temperature is discussed. The differential thermal analysis (DTA) technique was applied to measure glass transformation and crystallization temperatures, Sintering of selected coal ashes was performed as a function of temperature in air. The mechanical properties of sintered ashes were measured below and above the glass-transformation temperature, T-g. It was found that sintering propensities of amorphous ashes and superplastic-like deformation of deposits above T, depend on mass transport phenomena in the intergranular liquid phase.