Vavrus Builders of Joliet, Illinois chose concrete instead of limestone when they added 6 stories to an existing 12-story limestone-faced building in downtown Chicago. There were good arguments against using limestone for the new work. Not only does limestone cost slightly more per cubic foot than concrete, but it is a basically weaker material. At the required thickness of 5 inches, the largest possible limestone unit of the necessary strength could be no more than 12 by 18 inches. These small panels would in turn require many more hardware connections, more joints and more caulk, along with the labor necessary to complete the work. The cost of using precast concrete for the facing turned out to be only half of the projected cost of using limestone. Cast from 8 master molds, the 85 panels range in size from 1x2 feet to 9x12 feet. All panels are 5 inches thick and contain No. 5 rebars.