Abstract: A supporting element for use in casting concrete floors on a foundation includes a base member and a distinct top member supported by the base member. The top member has an elongated top sliding plane surface allowing a concrete leveling device to be moved along it. The base member is typically formed of side walls with openings in them, each making approximately the same angle with respect to the top member and being inclined so that they form an angle of about 25.degree.-90.degree. with respect to each other. The base member may form a groove in a central top portion of it, and the top member may be an elongated rail received within the groove. Foot portions connected to the side walls may have level adjustment screws provided in them for adjusting the position of the top sliding plane surface.