I had an interesting conversation recently with a classic car dealer located north of Detroit. I was at his shop inspecting a 67 GTO for an overseas client. The car was a pretty nice example, clean and well sorted, and I was enjoying my morning looking at it.

As I was surveying the exterior sheet metal, I noticed that I seemed to have attracted the dealer’s attention as I was spot checking different areas of the finish with my paint meter. After a couple minutes, he spoke up. He wanted to know what kind of meter reads I was seeing as I went around the car. I told him it was pretty consistent; about 15-20 mils all the way around, which was about what I was expecting considering there were at least 3 different coats of paint on the vehicle. I explained that while the car was originally painted Champagne Poly, and was that same color today, I saw little hints in many of the nooks and recesses around the inner bodywork that the car had, at some point in the past, undergone a color change to a blue shade. I had already magnet tested all the sheet metal, and run my meter around all the common rust areas on A-body cars, hunting for filler, but found virtually none- a solid car still wearing its full original rear quarters.

The dealer lamented to me about another inspector who had been there a few weeks prior. That inspector, he told me, went around the car and found the same 15-20 mils of thickness on the body and declared to his client “the car is full of Bondo!”- effectively killing the sellers potential sale.

I had to laugh at that- and cringe at the same time. That inspector, and inspectors like him are the reason why so many sellers look at pre-purchase inspections with disdain. I hear stories like this more often than I should; inspectors who put way too much faith in a paint meter, and don’t bother to analyze other hints and clues about what may be really going on with a car. A meter should only be used as one tool in a competent inspector’s tool-kit, and as a tool, it’s only as useful as the person who’s interpreting the numbers and paying attention to other details.

For those who may not know, paint meters, otherwise known as coating thickness testers, are electronic devices used for testing the thickness of different types of coated materials (usually metal) using an ultrasonic signal that is converted into a thickness measurement usually denoted in “mils”. 1 mil equals .001”. So, if you have paint on your car that is 5.5 mils thick, your paint is approximately .0055” thick. As a point of reference, a dollar bill is .0043” (or about 4.3 mils thick), and the average paint thickness on that supposedly Bondo filled GTO with its several coats of paint I looked at was about .017” thick. That’s about as thick as three dollar bills stacked on top of each other. As a very broad generalization, OE paint from the factory generally runs anywhere from 2-6 mils (.002-.006”) in thickness, depending, of course, on a variety of factors.

Of course, mis-interpreting meter reads can work both ways. I was recently out of state looking at a beautiful Lincoln Continental for another client. The car was advertised as completely original, un-restored, with just over 16,000 original miles. My client interpreted the ad to mean the car was wearing its original paint as well. When I first arrived, I did a high level walk-around of the car, and took some meter reads- which were hitting between 2 and 5 mils in various places. A little inconsistent, and when I started seeing reads in the 5 mil range, I became quite suspicious of the finish being original. I decided to check out the rest of the car for any tells that would confirm my suspicions and come back to assessing the bodywork. I found what I needed to under the hood. To a casual observer, the engine area was immaculate; the only notable visual let-down’s being some in-correct style hose clamps, parts store coolant hoses, and a NAPA replacement ignition coil and plug wires. For a 16,000 mile original survivor, I’d have sourced proper OE marked era-correct components, but that’s just me. Looking in the deep recesses of the engine area however, there was ample evidence that the inner wheel wells had been re-painted body-color. You had to look carefully, but there was subtle overspray on the transmission cooler lines off the radiator, a few small spots of overspray on portions of the wiring harness, and masking lines around several of the black plastic harness clips attached to the sheet metal. Someone had spent some time covering everything up as best they could before re-painting, but the evidence was there. Going back over the bodywork much more carefully, the evidence I needed was there too; very subtle but unmistakable masking lines on several pieces of chrome trim, and a very faint hint of body-color overspray on a couple of weather seal pieces and I suddenly understood why I was seeing 5 mils of paint in places. The car has been at least partially re-painted (I believe the roof paint is original), which was a deal-killer for my client, who is only interested in completely original cars, including paint. These minor details made all the difference to him, and I could have gotten it all wrong had I just “relied on the meter” and not studied the other details carefully.

So the next time your inspector says your potential purchase is “full of Bondo”, ask them how they know that. Did they perform magnet and meter tests on the bodywork? To be sure, there are many classic cars on the market today that do have sizable areas of filler used to hide previous rust or accident damage. Since our inspections are on video, we have the ability to actually show our clients on camera with the tools we use where any notable filler is located on the classic they’re considering and discuss what paint meter reads actually mean- an important part of any competent pre-purchase inspection.

Happy Motoring.

John Hansen is an automotive writer and owner of Michigan Automotive Inspection Services, which provides professional pre-purchase inspection, consultation, and appraisal services for classic automobiles located all over the United States.