The ornamental design for a tilemortarjoint, as shown and described.
FIG. 1 is an end view of the tile mortar joint showing my new design; and,
FIG. 2 is perspective view of the tile mortar joint which extends both along a side of a tile and orthogonally across an end of a tile.
The dotted line representing tiles and a substrate for supporting the tile mortar joint are for illustrative purposes only and form no part of the claimed invention.