HOW TO REPAIR RUST SPOTS ON A CAR

Without a doubt, one of the most commonly misused terms when it comes to rust is "surface rust". As the owner of a bodyshop specializing in custom and classic cars, I see this far too often. Many people firmly, but wrongly believe that if the rust hasn't formed a hole yet, it's surface rust. Probably the easiest way to determine this is to check if the paint is still over the rust. If the rust hasn't broken through the surface of the paint, you know that rust couldn't have come from the surface of the metal. It came through from the inside, and is therefore not surface rust. True surface rust is when the paint has been removed, usually by a scratch or chip, and the exposed bare metal begins to rust. It is vital to know and understand the difference before attempting any rust repairs.

If you have true surface rust, simply sanding or grinding out all the rust from the area is sufficient to remove it. It will be necessary to also roughen up the surrounding area so a thin layer of filler can be applied to smooth out the repair. The area under the filler needs to be rough (course sandpaper will take care of this), in order for the filler to adhere properly.

I keep a section of a body panel at my shop to demonstrate how rust is commonly misunderstood, and therefore misdiagnosed. From the outside, the paint still looks good other than some bubbles that are concentrated in one area. The customer that brought me this particular car told me it just had surface rust. He was convinced that I could simply grind it down and the rust would be gone. Decades of experience dealing with rust provided me with the knowledge that it was more than surface rust, and when I cut out that section of the car's body, I saved it to show the customer. Although the outside visible damage consisted of bubbles in an area about 2 inches by 6 inches, the inside of the panel was coated in rust, about 6 inches by about 18 inches. In a matter of months, if not less, that rust would have come through if I had repaired it the way the customer believed was sufficient.

This is a very common mistake and I have even seen professional body shops misdiagnose surface rust. This is why shops don't guarantee rust repairs. This is also the reason you see rust on a car that was just painted a couple of months earlier. The person who fixed it likely thought it was just surface rust, simply ground it down (if that), possibly applied some filler

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