Abstract: A tool that can be used to join adjacent deck sections along their side edges. the tool can include a handle portion that is used by the operator to maneuver the tool and a cutting assembly that is at the base of the tool. The cutting and folding assembly can further include a driven punch that operates with a stationary die to simultaneously cut and shear the horizontal elements of a side lap, then folds those elements downward about 90 degrees from their original horizontal position, hemming the two individual side laps into a flattened vertical seam.