Abstract: In forming settable mix into hollow-cored articles, cantilevered hollow core-forming mandrels are disposed in a mold station, each mandrel being wrapped in a flexible, non-porous casing formed as an endless loop slip-case which encloses the exterior and interior mandrel walls. Movement of the mix moves the casing along the longitudinal mandrel axis rotating it around the exterior and interior mandrel walls, thereby preventing the accretions of settable material on the mandrel.