The evolution of contact pressure at the metal/mold interface in an idealized, directional solidification process is examined using a thermohypoelastic stress function and the Neumann temperature solution. Nonuniform thermal distortion of the casting is established through the application of an oscillatory temperature profile at the mold interface. This is an attempt to study the effects of the often highly irregular cooling profiles in typical industrial casting processes (albeit in an idealized fashion). In many of these processes, it is virtually impossible to cool the ingot uniformly due to a variety of process conditions. Nonuniform thermal distortion causes the contact pressure at the mold interface as well as the macroscopic freezing front morphology to oscillate. If the contact pressure exceeds the hydrostatic pressure of the residual molten metal to the point where its net value is zero, then an air gap is nucleated. This represents a condition in which the casting and the mold surfaces locally begin to separate. If air gaps nucleate beneath the thinnest sections of the undulating freezing front, then a condition of growth instability exists since further heat extraction beneath these regions is significantly reduced. The thickest regions of the casting continue to grow due to improved contact and hence the freezing front nonuniformities become significantly exaggerated with time.