Cementitious building panels are connected together using a connector plate made of a composite material of carbon fibers embedded in an organic matrix. The interconnection is made by removing cementitious material to form recesses in the building panels, applying an adhesive material into the recesses prior to placing the connector plate into the recesses, and thereafter affixing the connector plate to the first-panel face and to the second-panel face in the recesses and extending across the gap between the first-panel edge and the second-panel edge.