Abstract: A tundish used in a continuous steel casting operation is sealed to permit effective purging of the tundish to eliminate free oxygen and nitrogen by providing a plurality of generally rectangular planar sealing boards of refractory fiber material having sufficient density to be self-supporting and placing the boards in side-by-side relation on the open top of the tundish prior to installation of the refractory cover whereby the sealing boards form a gasket between the cover and tundish top wall, and form a continuous panel underlying the cover. The refractory fiber material may be penetrated by the ladle shroud tube and/or the tundish stopper rod(s).