What a paint depth gauge actually tells us
Why we measure every panel before we quote, what a reading over 200 microns usually means, and when a reading makes us stop.
Written by Tom Hartley, who has corrected more of them than he would like to count.
What the numbers mean
A gauge reads the total thickness of everything on top of the metal: primer, colour and lacquer. Factory paint is usually somewhere between 100 and 180 microns, and the clear coat on top is only 35 to 50 of those.
That clear coat is all we ever work in. It carries the gloss and the UV protection, and it is the only layer polishing can safely touch.
Why a high reading matters
A panel reading well over 200 microns has almost always been resprayed or filled. Refinished paint can be softer, thicker or thinner than factory paint, and it does not always behave the same under a machine.
That is not a problem, it is information. It changes the pad, the polish and how many passes we are willing to make.
Why a low reading matters more
A panel reading 80 microns has been polished hard before, or has thin factory paint. There may be only twenty microns of lacquer left. A single stage takes one to three of those.
On a panel like that we correct gently or not at all, and we tell you which panels we left alone and why.
What we do with the readings
They go on a sheet, before and after, panel by panel, and that sheet goes home with the car. It tells you what was taken and what is left for next time.
If someone is quoting you for correction without measuring, they are guessing with a layer of paint you cannot replace.
