Once a car is painted, it’s nearly impossible to know what is under the pretty shine. Ideally, the body work was done correctly by stripping the old paint, pounding out minor dents, and replacing damaged or rusted panels. A good paint job like this will have almost no filler and the correct thickness of paint.
Older cars frequently have a thick layer of 2-3 previous paint jobs and body filler underneath. That thick layer will eventually shrink unevenly over time and causes cracks and blemishes in the painted surface.
The other danger is that some body shops use filler as a rust “Fix-All”. Instead of properly repairing rusted panels, they simply cover it with filler. The panel will look OK for a few years, but the hidden rust continues to grow and will eventually cause paint blisters.
An experienced appraiser will check the body and frame thoroughly for the rot that is visible. To find the hidden rust, choose an appraiser who uses a Paint Depth meter to determine where the filler is located.
The Paint/Filler Depth Gauge can also determine whether the body paint is original, or if it was been repainted.
The paint depth meter uses a digital readout to show the distance between its tip and the nearest metal surface. The meter’s tip is smooth so it does not damage the paint surface. The paint depth meter readings are in thousands of an inch (.001”). Here is what the paint depth meter readings mean:
A normal paint job will be in the 4-8 range (.004-.008”).
Repainting over the original paint will be in the 7-15 range.
The areas over 15-28 may have a thin “skim coat” layer of filler to level minor dings in the panel.
Some areas may read “Infinity”. Infinity means the filler was so thick that the metal could not be detected.
The paint depth meter does not work on non-metal panels like fiberglass or plastic.