Using colloid water as a covering for explosives can improve the energy efficiency for explosive welding, while its effects on bonding properties remain unclear. Here, by employing titanium/steel as a model system, the effect of covering thickness on microstructures and mechanical properties of the bonding interface was systematically investigated. It was found that all the welds displayed wavy interfaces, and the wave size increased with increasing covering thickness. Vortices characterized by solidified melt zones surrounded by strongly deformed parent materials, were only formed for the welds performed with a covering. Moreover, with increasing covering thickness, both the tensile strength and the elongation of the titanium/steel plate decreased, and the failure mode changed from ductile to cleavage fracture, gradually. In the tensile-shear tests, all the fractures took place in titanium matrix without separation at interface, indicating that the titanium/steel interfaces had an excellent bonding strength. The micro-hardness decreased with increasing distance from the interface, and this trend was more remarkable for a thicker covering. The micro-hardness inside the solidified melt zones was far higher than that observed in strain-hardened layers of the parent metal, due to formation of hard intermetallic compounds.