A spreading device (10) for the spreading of bulk material on a circular surface comprises a distribution plate (12) mounted about a central shaft (14); at least one radially extending slit (16) arranged in the distribution plate (12); and a scraper device (24) for spreading the bulk material over the length of the slit (16). The bulk material is preferably granular or powdered covering material to be deposited as an insulation layer on the top layer of a casting mould containing molten steel or metal. According to the present invention, a rectangular distribution trough (22) mounted on the distribution plate (12), the slit (16) being arranged within the distribution trough (22). Furthermore, a feed pipe (30) is arranged so as to feed bulk material into the distribution trough (22) onto an area corresponding to the rotational centre (18) of the distribution plate. The slit (16) extends from the rotational centre (18) of the distribution plate (12) to the edge (20) thereof. Finally, the scraper device (24) comprises at least one linearly displaceable scraper (28) arranged within the distribution trough (22) so as to feed the bulk material through the distribution trough (22) radially outwards from the rotational centre (18) of the distribution plate (12). The invention also relates to a method for applying a homogeneous layer of material onto a circular surface by using such a spreading device (10).