Abstract: The invention concerns, for combination with a corner defined by an upright wall, and a generally horizontal surface as defined by a bath tub or the like, and cured mastic applied to said corner, the following:(a) a longitudinally elongated, plastic strip, which is generally crescent shaped in cross section, the strip having terminal edges defined by laterally spaced lips adapted to be supported adjacent the wall and the surface so that the strip confines the mastic in the corner in strip installed position,(b) the mastic in cured state being incompletely rigid,(c) and barb structure integral with the strip and projecting therefrom into the mastic, which in cured state anchors the barb means to retain the strip in said installed position.