Abstract: A rotational viscosimeter is used for determining the flow properties of flowable mixtures having coarse grain components; the device includes a pot with a centrally journaled, rotatable cylinder therein wherein the annular gap between the inner cylinder and pot is at least five times greater than the largest particle diameter of the solids located in this annular gap, there is a sealing liquid located in the pot under and around a lower end of the inner cylinder at least up to the lower lip formed thereon. The surface of the inner cylinder and/or the inner surface of the pot beyond the sealing liquid level is roughened or provided with grooves.