The effect of alumina platelet inclusions on the sintering behaviour of a commercial alumino-silicate glass powder has been investigated by means of a heating microscope at 850-degrees-C. For platelet volume fractions less-than-or-equal-to 0.1 5, no significant influence of the inclusions on the densification behaviour of the composite was found. Scherer’s model for viscous sintering with rigid inclusions, which uses the Hashin-Shtrikman approximation for the composite shear viscosity, can be conveniently used to interpret the experimental results. However, the composite densification rate and the stresses caused by the inclusions can be correctly predicted using this model only for inclusion volume fractions lower than a critical value, given by the percolation threshold. For platelet volume fractions less-than-or-equal-to 0.1 5, high-density glass matrix composites can be fabricated by simple pressureless sintering.