Drywall corner-finishing accessory

A drywall corner-finishing accessory comprising three integrally joined, elongate strips, namely two relatively rigid, lateral strips and a relatively pliable, middle strip, each lateral strip having a broad portion with a distal edge and a proximal edge and having a rib with a distal edge and a proximal edge merging with the proximal edge of the broad portion of such lateral strip, the middle strip having two opposite edges and a generally uniform thickness substantially between the opposite edges and being joined at each of the opposite edges to the rib of one of the lateral strips at the distal edge of the rib thereof, the accessory being flexible along the middle strip, between the opposite edges of the middle strip, selectively to define a stepped, inside corner, in which the ribs are directed inwardly so as to constitute means for guiding a tool used to apply drywall-finishing material over the lateral strips, in which the middle strip has a concave surface stepped inwardly from the broad portions of the lateral strips and curved substantially between the ribs of the lateral strips, and in which the relatively pliable, middle strip serves as an expansion joint, and to define a stepped, outside corner, in which the ribs are directed outwardly so as to constitute means for guiding a tool used to apply drywall-finishing material over the lateral strips, in which the middle strip has a convex surface stepped outwardly from the broad portions of the lateral strips and curved substantially between the ribs of the lateral strips, and in which the relatively pliable, middle strip serves as an expansion joint.