Abstract: A wall formed from square edge predecorated wallboards and the method of constructing a seamless wall from square edge predecorated wallboards comprising folding the edge flaps of two abutting square edge wallboards away from the joint, cutting a groove along the length of the joint formed by the square edged abutting wallboards, adhering a joint strip comprising a rib which fits within the groove and a support strip therefor which extends laterally over the uncovered portion of each gypsum board adjacent to the joint, and double-cutting and adhering the edge flaps of the wallboards to the joint strip so as to form a seamless appearing joint.