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Paint Removed by Abrasive polishes

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Posted 05 July 2012 - 03:15 AM

With a clear coat thickness of ~49µ and knowing that most of the ultra violet protection is in the top 50% (~24.5µ); therefore, limiting UV protection removal to ~25 % means that approximately 6.125µ< can e removed before the ultra violet protection is compromised. Once you remove too much clear coat you'll have no paint UV protection other than what you apply with a LSP (providing it contains UV protection.

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

Relevant Articles

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 - 05:34 AM.

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#2 SVR


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Posted 04 January 2013 - 04:31 PM

Top notch mate. I was told by my mentor and fourty year veteran of detailing that using the single polish system his company makes with rotary and a wool pad will remove 3.83 microns from most paints.

a compound or traditional compound would remove more I'd say as they gouge paint not cut it
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#3 Ron Ketcham

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Posted 04 January 2013 - 05:32 PM

In my decades of working with the paint engineers and the paint suppliers to USA automotive manufacturers, the use of "mil" is the standard, not micron.
Micron is the term used by most Asian and European manufactuers, but not in the USA.
Studies by these paint engineers and paint suppliers state that the removal of excess of .3 mil (1/3 of a mil) will usually compromise the UV protection that is part of the clearcoat. There are some old figures still floating around that stated the .5 mil (1/2 mil) is a safe number.
Part of the curing process of OEM clear coat material causes the majority of the UV blockers to rise to the top .5 mil of the clear.
Which is why they changed the "safe removal" amount to .3 mil.

#4 Accumulator


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Posted 05 January 2013 - 09:50 AM

Hope people read this and take it seriously.

Ron Ketcham- I can't tell ya how or why, but I've somehow gotten accustomed to thinking in terms of microns instead of mils :think: :nixweiss Maybe I like the finer graduations.

Hey, do you happen to remember what the "standard oem thickness" (scare-quotes intentional ;) ) was for the Ford Panther platform cars? IIRC it was around 4.5 but I can't tell ya why I think so. No, I haven't found an umolested area on mine to measure (and I hate my current ETG), just wondered if you had a figure rattling around your memory.
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#5 Ron Ketcham

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Posted 05 January 2013 - 09:58 AM

Really doesn't make a difference on what "platform" for US production of Ford, the set standard was set by Vehicle Operations in Allen Park and were for base/clear or single/intergrated systems.
You will "never" find a consistant total film build, IE-always 4.5 mil or such on any vehicle.
Coming out of the oven they can vary by 1/3 to 1/2 of a mil.
Crown Vics and Gran Marquis of 1990 to the end, usually were between 4.5 and 5.25 mil total film build right up to when production ended
Same with Wixom production.
There was less stringent concern and quality control on paint film buildwith the lower priced models.
With the exception of Dearborn and later, Flat Rock Mustang production.



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Posted 05 January 2013 - 01:30 PM

Film thickness can be measured in two ways. The first and more common and standard measurement are called mil. A mil equals 1/1000 of an inch. A typical factory paint job will measure between 4.0 and 6.0 mils. The clear coat will generally measure between 1.5 - 2.5 mils

The alternative measurement is called a (µ) micron, which is a metric unit that equals one millionth of a meter, or 1/1000 of a millimetre. A micron (µ) is much smaller than a Mil; there are 25.4 millimetres in an inch. This is the unit used in Lab testing and also standard in the EU

I use the micron measurement because it's so much smaller. One micron is roughly 1/80th of the thickness of a human hair (hair thickness depends on hair colour/ethnic origin etc) I always want to know where I am at all times in terms of paint removal. If you are going to get into heavy correction such as wet sanding, you will be quickly removing clear coat, and will need to keep track of how much is being removed, and will need to be accurate. Micron (µ) readings will constantly change as I sand; keeping me constantly informed of how much is being removed, and will need to be accurate. A mil reading will not change that rapidly during the process.

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#7 Ron Ketcham

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Posted 05 January 2013 - 05:02 PM

Jon, there is so much of what you say that is exactly correct.
However, in the "real world " of dealing with the subject, it has to do with just that, "real world" and all the books, studies, etc do NOT present such in a manner that the average person is able to use as a determination and use in their world.
Plus, "things change" and sources may be outdated.
They who read and take to heart, may not or are not of a degreed engineering back ground, they do not have access to the expensive tools and such to make eductated determinations of what is the "total film" build, they do not have chemical degrees to be aware of the composition and such of yesterday's or today's paint systems used by vehicle manufacturers on vehicles.
In my years of actually "working" in the "car care industry", the "paint systems", with major vehicle manufacturers and their assembly plants, their paint engineers, their "dealerships", all around the world, I found an easy way to communicate the thickness of the "average" clearcoat thickness on an original paint system.
It is quite simple to make the point. (please keep in mind that while doing such, I would often be working with the lowest pay scale, etc employee at a dealership)
Take the "wrapper" off of a pack of cigarettes, place it, with "both sides" compacted and using a modern, digital electronic measuring devise, measure the thickness.
That---is the "average" thickness of a factory applied clear coat!
The measurement results will show 1.5 to 1.75 mil on average(some may go to 2 mil) and that is the "clearcoat" thickness, no matter what plant, what country, etc. That's the way it is.
The "measurement" allowance you posted are a bit behind the times, as far as "allowable removable" and I base that on the data I received from Ford, Chrysler and GM- 5 years, repeat, FIVE years ago before I retired from working with them.
.3 mil, IE 3/10th of a mil of removal of clear from an OEM applied clear is the standard. That is NOT in regards to "refinish applied" clears, as that is very variable in regards to the supplier of the clear materail and their "instuctions", and the "wishes" of the painter, etc.
Once people see this or accept that is all they are dealing with---"the lights, hopefully, come on".

#8 Accumulator


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Posted 06 January 2013 - 10:08 AM

Ron Ketcham- Thanks for the info (and "heh heh, yeah...." regarding all those disclaimers ;) ).

On the variations of oem paint thickness- even cars like my Audis, done with "modern" robotic [crap], aren't uniform. Not by a long shot.

TOGWT- I think you and I see the "micron v. mil" thing similarly. Heh heh, I gotta search my character INSERT for that mil symbol :think:
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