Methods for making an environmental barrier coating using a sintering aid involving: applying a bond coat layer to the ceramic component; combining at least water and a primary transition material selected from a rare earth disilicate or a doped rare earth disilicate to produce a transition layer slurry; applying at least the transition layer slurry, and optionally an outer layer slurry and/or compliant layer slurry to the component; and sintering the component to produce the environmental barrier coating. The sintering step causes a reaction between a slurry sintering aid and constituents of at least one of the transition, outer and compliant layers to form a secondary material and reduce porosity in the coating.