A thin semi-rigid preformed elongate strip for disposition at the junctions of adjacent drywall wallboards or between sections of a plaster wall to absorb movement within a wall without detrimental effects therefrom, having two outwardly directed opposed flanges arranged for affixation to the wallboard or the lath outer face along adjacent edges, an adjoining central flexible bent portion arranged to be disposed below the general surface plane of the wall between adjacent edges of boards or sections thereof, and adjoined along its lateral edges to the two flanges, and an upwardly extending screed formed in each flange. In the preferred form, a flat strip extends across the central portion on the face of the strip. This may be of different material and more flexible, and may be formed for rapid removal after completion of the wall construction.