A method is provided for repairing defects in a ceramic core adapted for use in a casting process. The ceramic core is formed from a slurry comprising at least one refractory powder material suspended in a liquid vehicle. The method includes forming a repair mixture comprising a liquid diluent and the at least one refractory powder material suspended in the liquid vehicle of the slurry. The repair mixture is applied to a region of the ceramic core that includes at least one defect and then the ceramic core is fired to burn off the liquid vehicle in the repair mixture and form a ceramic composition that closes the defect.