We employ the theory of two-phase flow to investigate the influence of grain boundary wetting during segregation of magma in a partially molten aggregate. In partially molten aggregates the `disaggregation melt fraction', the volume fraction of partial melt at which grain boundaries are completely wetted, is crucial in determining the total interfacial force per unit volume. Surface tension on grain boundaries in melt fractions less than the disaggregation melt fraction tend to homogenize melt distribution when the solid-liquid interfacial tension is smaller than the interfacial tension arising from grain boundaries. We also demonstrate that in the presence of large grain-grain interfacial tension, the solitary wave solution to the mass, energy, and momentum equations for two-phase aggregates becomes dissipative. Under such conditions, the rate of buoyancy driven melt segregation is reduced due to melt retention by grain boundaries.
