A hybrid explicit-fully-implicit numerical simulation model that conserves solutes is used to study the dissolution process during the equilibration stage of wide-gap brazing, and the numerical simulation results are validated with experimental data. In contrast to what has been commonly reported, the study shows that notwithstanding the high solute diffusivity in the liquid-phase, instead of seconds and few minutes, the dissolution stage can take hours to attain completion, depending on the gap size. This is attributable to the occurrence of rapid and large reduction in the solute concentration gradient in the liquid during the early stage of the dissolution process. Moreover, by keeping the two key factors that are generally known to influence the extent of isothermal solidification during brazing, temperature, and time, constant, it is found that initial gap size can also alter the extent of isothermal solidification, due to its influence on the dissolution process. The study further confirms that it is possible to use powder mixture that contains base-alloy additive powder, as interlayer material during wide-gap brazing, without partial melting of the additive powder particles, which can be crucial to the properties of brazed single-crystal and polycrystalline alloys.