in phantom in fig6 may be secured across a series of slits 70 or other perforations in the leg 64 in order to fasten the member 60 to the outer face of the sheet 30 in the appropriate manner a layer 72 of mortar completely covers the leg 64 in order to conceal the same and to provide a smooth transition between the face of the sheet 30 and the lower edge extremity of the member 60 fig1 13 and 14 illustrate sequential steps in the method of preparing a joint 56 or 58 in accordance with the present invention as illustrated in fig1 the partition 28 is initially erected in the usual manner leaving the gap 40 between the bottom surface of the ceiling 14 and the upper marginal edge of the partition 28 then as illustrated in fig1 the special member 60 is stapled or otherwise secured to the face of the partition 28 in such a way that the leg 62 of member 60 projects outwardly away from the partition 28 and into the roomspace at the same time that it butts up against the underside of the ceiling 14 thus the leg 64 of member 60 completely covers and conceals the gap 40 next as shown in fig1 the layer 72 of mortar is applied in convering relationship to leg 64 so as to completely conceal the latter in this connection application of the layer 72 is quickly easily and neatly carried out by the finisher as it is only necessary for the finisher to apply the mortar in a smooth sweeping stroke along the leg 64 with the edge of his trowel butted up against and running along the horizontal leg 62 thus the leg 62 not only serves to.