A prefabricated modular joining assembly for an industrial flooring comprising a module including a prismatic body formed by two half-portions, being separated from one another by a deformable material zone, said half-portions being made of a synthetic resin and having a metal reinforcing framework embedded therein. The joining assembly is made by a method comprising the steps of: providing a box caisson; arranging a rubber membrane in the box caisson thereby separating two zones of the box caisson; arranging in the two zones a reinforcing metal framework; casting a resin material in the box caisson thereby embedding the reinforcing metal framework therein; removing, upon setting of the resin, the module thus formed; and applying the module in a recess formed in a floor at a joint to be restored.