When water contacts bare metal, rust forms on the surface of the metal. If left unchecked, rust can eat through the metal, resulting in a hole. A rust hole compromises the structural integrity of the metal. Repairing rust or a rust hole on metal without welding requires a material that bonds and is as strong as metal. Two-part epoxies are designed for this purpose and when applied to a clean surface, the final repair will be undetectable after painting.
Attach a 60-grit flapper wheel to a 4.5-inch angle grinder and put on your safety glasses.
Pull the trigger of the angle grinder and run the spinning 60-grit flapper wheel over the rusted area of the metal. While sanding the rust from the surface of the metal, the rust damage will be exposed and there is a chance that the rust hole you need to repair will grow larger.
Wipe the sanded surface of the metal with a clean rag to remove sanding dust and debris from the surface of the metal.
Thoroughly mix equal parts of the two-part epoxy putty. You need to mix enough two-part epoxy putty to cover an area at least twice as large as the rust you need to repair. If the repair area is large, you may need to mix the two-part epoxy in stages to allow you time to apply the epoxy putty before it hardens.
Place the mixed two-part epoxy putty on the area of the metal you need to repair and work the epoxy putty onto the surface of the metal by apply pressure on the epoxy putty with your thumbs and fingers. Make sure that no air remains between the two-part epoxy putty and the surface of the metal.
Allow the two-part epoxy putty to cure for the time specified by the epoxy installation instructions.
Remove the 60-grit flapper wheel from the 4.5-inch angle grinder and attach the 80-grit flapper wheel to the 4.5-inch angle grinder.
Sand the cured two-part epoxy putty with the 80-grit flapper wheel to blend the rust repair into the surface of the metal to complete the rust repair.
Prime and paint the metal immediately after the repair is complete; this will avoid rust from returning to the repair area.