Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

December, 2005

Paint Thicknesses

Q. I just bought a brand new GMC Envoy. I noticed that the rear door was not shutting well. I thought that maybe the truck had been wrecked. I took it to a shop that has a mil gauge. The entire truck had mil readings of 9.5 to 11.8 on the body. I measured another "New" truck & had readings of 4.2 - 5.7. I can't find any overspray or evidence that the truck has been repainted. Any thoughts?

A. The film thicknesses are high and do suggest that the vehicle was repainted. I don't know of any non-destructive test that can show what paints were applied. However, there is a film thickness gauge that scribes a "V" through the paint, all the way through to the substrate. Using a magnifying glass that comes with the instrument you can count the number of distinctly different colored coats that have been applied and measure their respective thicknesses. You might find that after the topcoat was applied by the GM assembly plant, the previous owner or Dealer applied another coat of primer followed by the topcoat. To do this you must be willing to put a 1" - 2" scratch into the coating and repair it after you've done the test. Better still if you were able to cut a 1" x 1" piece of painted metal or plastic from an area of the vehicle that nobody can see, you can conduct microscopic and even analytical tests to determine if the topcoats were applied by the assembly plant or by a body shop. Unfortunately, this does mean that you would need to destroy something on the vehicle.

Q2. Thank you for your timely response. The vehicle was sold to me as New. It had 22 miles on it, so no previous owner. I think it was re-painted at the factory-does that happen? The shop that looked at it used an ETG mil gauge that he said cost $1500.00 & is very accurate. It has NO over spray anywhere, leading to my thinking it was repainted before being fully assembled. Am I correct in assuming that if it ever needs a repair that they cannot blend on to the adjacent panels due to existing excessive paint? Thanks again for your response.

A2. It is entirely possible that the assembly plant repainted the vehicle, or at least some of it. This is not unusual especially when small paint defects, such as dust particles are caught by the quality control department. If it was repainted at the assembly plant, you should not be concerned because they will have used the same coating and followed the same baking schedule.

With regard to color matching in there future you should not experience any different problems that you would not have had if the vehicle had been painted one time only.

Best wishes,

Ron Joseph

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