Be cognizant that ultra violet protection removal is not a liner process; and the first paint renovation will remove the most UV protection, therefore the above are probably conservative estimates. Two variables need to be established; how much clear coat is available and how much clear coat can be removed without compromising the paint systems long-term durability / paint warranty
Order of magnitude: standard printer paper or a one dollar bill 76 µ (micron) (3 Mil), a standard sandwich bag 25.5 µ (1 Mil)
A paint thickness reading of > 4 Mil ( 100 µ (Microns) is reasonably safe for polishing. 3 – 3.5 Mil ( 80-90 µ) I wouldn't use anything stronger than > 2000 grit polish, 2.75 – 3.0 Mil (70-80 µ) > 2500 grit polish and under 2.75 Mil (70 µ) use a glaze. The readings tend to vary from panel to panel and are thinner towards the panel edge.
Most light surface marring is ~1.27 µ (0 .05 Mils) a surface scratch that can catch your fingernail is ~1.01 µ (~ 0.04 Mils) Using a medium abrasive polish and a rotary polisher will remove approximately ~ 2.5 - 3µ (~ 0. 98 – 0.12 Mil) from the paint surface. To remove a scratch you need to level the paint to its lowest part, so if a scratch is 1 µ that’s the amount of paint (and UV protection) you need to remove to eliminate it.
• 200µ + can be expected on older cars that have been hand painted or a re-painted vehicle
• 100 – 200µ 4 – 8 mil - normal paint thickness
• 80 – 100 µ - 3 – 4 mils, thin paint
• 80 µ < - less than 3 mil, very thin paint
The following are the maximum allowable clear coat reductions the major USA car manufacturers will allow before the paint warranty becomes void; Chrysler- 0.5 Mil (12µ) Ford – 0.3 Mil (7.5 µ) GM – 0.5 Mil (12µ) (Source - Automotive International)
Rotary polisher: using a medium abrasive polish and a rotary polisher will remove approximately 2.5 - 3µ(micron(0. 13 Mil) from the paint surface, which is typically four passes at 1500-1800 RPM; however many variables such as polish/compound and speed / pressure used that may affect the paint removed)
Paint renovation / correction; wet-sand using 1500, 2000, 3000 grade finishing paper, polish to remove sanding scratches (using medium and fine abrasives) will remove approximately 5 µ (0.2 mil)
Random orbital polisher: using a medium abrasive a cutting pad, speed #5 will remove ~ 4 µ (0.17Mil)
These numbers are offered as a guide only, as there are too many variables to provide any more than an approximation.
The key to the polishing process is to know how a particular paint will react with each step you are performing. Once you know that scratches and imperfections are fairly easy to remove, you’ll have the confidence to do what it takes to remove them.
Common sense dictates that if you want to remove a scratch, then you must remove some of the material (paint, glass, etc) to get down to the bottom of the scratch. Most new car finishes can be properly maintained without using abrasive polishes. It just means working smarter not harder, proper washing, drying and applying paint protection and the correct maintenance of a paint surface is the solution. As well as the use of proper tools and methodologies, pro-active finish damage avoidance is the best way to maintain a perfect finish.
If you have reservations about the amount of paint surface removed or the amount of paint coating remaining the use of a paint thickness gauge (PTG) is arbitrary. There comes a point when you must judge wither removing a scratch will compromise the clear coat and if so you’ll have to ‘live’ with the imperfection, or use a Glaze; their filling abilities are sometimes used on vehicle with thin paint, were further polishing would compromise the paint. It’s interesting to note that painters must now demonstrate proficiency with an electronic paint thickness gauge in order to become certified to perform paint refinish warranty work for General Motors Corp. (GM) vehicles
Automotive paint, even if it the same model year and colour will often vary in density (hardness) and thickness, dependent upon the OEM paint specification and paint curing process, which can vary by vehicle assembly plant.
Considering the differences in automotive paint and the variables encountered in polishing ( machine and linear speed, pressure, different polish / pad combinations, etc) Making a statement like if X microns are removed by paint correction I can do this Y times during the lifetime of the paint system would be profoundly inaccurate.
Long-Term Paint Care
A better long-term approach would be to bring your paint system up to a standard you’re satisfied with and ensure you use a proper paint washing technique (2 buckets with GritGuards or Optimum ONR) then add one of the newer paint coating products (Opti- Coat™) which once cured has a scratch resistance and a thickness of 2-4µ, which is similar to OEM clear coat
1. “Clear Coat Thickness and UV Protection Removed by Polishing” - http://www.autopia.o...n-removal.html#
2. “Difference between Diminishing and Standard Abrasive Polishes" - http://www.autopia.o...epost&p=1472657
3. “Long-term Paint care” - http://www.autopia.o...paint-care.html
Edited by TOGWT, 06 July 2012 - 01:34 PM.