Remove the damaged plastic item. Clean damaged areas of the plastic with soapy water or a mild solvent degreaser. It must be clean of any fibers or molds.
Sand the area of the plastic needing repair. Use sandpaper of 80 grit. Round off edges and damaged areas. Join the damaged parts with foil tape.
Preheat plastic welding gun for 15 minutes. Determine the temperature needed for the plastic you are welding. Temperatures usually ranges between 500 to 550 degrees F. Moving the tip of the welding gun closer or away from the workpiece will help adjust the temperature.
Insert the plastic welding rod and damaged plastic into preheated welder. Feed the rod with a steady motion, moving the applicator tip along the joint. Allow enough time to cure. The rod will need to be of the same material as the object being welded.
Finish sanding. Use sandpaper with 150 grit. Then finish by covering the plastic with a water-based solvent.