The horizontal direct chill (HDC) casting process is a potential production route for magnesium remelt ingot. The ingot may sometimes suffer from surface and centreline hot tearing. In order to control these defects, an analysis of the hot tearing mechanisms based on crack propagation has been developed. The model builds on previous hot tearing models and calculates the pressure contributions acting on a nucleated tear due to feeding and capillary effects, to determine if the void will propagate. The influence of columnar and equiaxed structures on tearing is predicted.