We study the spreading of mercury droplets on thin metal (silver or gold) films on glass at room temperature, which is the only known system of reactive-wetting at room temperature. We show that there exist two main regimes, the bulk propagation regime and the interface kinetic roughening regime. In both regimes, rich spatio-temporal patterns are observed. We characterize these patterns using statistical physics tools, such as the growth, roughness  and persistence exponents, and show some recent exotic DLA-like patterns obtained in experiments.