Abstract: An interior corner joint for joining wall board panels, particularly wall board panels simulating tiles embedded in grout, in a corner. The interior corner joint comprises a first base section; a second base section extending upwardly from said first base section and being perpendicular to said first base section; a rib extending upwardly from said first base section disposed adjacent to said second base section and canted toward said second base section, said rib, second base section, and first base section defining a channel adapted to receive a first wall board panel; and a flange at the distal end of said rib extending outwardly from said rib and inclined toward said first base section, said rib, flange and first base section defining a second channel adapted to receive a second wall board panel in substantially perpendicular relationship to said first wall board panel. With the two wall board panels inserted into the two channels the only exposed part of the joint is the flange.

Abstract: An extension joint for use with wall boards simulating tiles embedded in grout. The extension joint is disposed between two adjoining wall board panels and simulates a grout line. The wall joint comprises a long narrow strip of material having two spaced apart base sections and a raised ridge section connecting the two base sections. The top outer surface of the ridge section is concave to simulate a grout line.