Wednesday, 27 May 2015

Clear Coat and UV Protection Removal


Clear Coat
A clear coat system consists of one or more primer layers, a flat colour layer and a glossy, clear top layer.  The primer is a corrosion inhibitor and a bonding agent for the bare metal and the colour layer.  It prevents corrosion and provides a stable substrate for the colour and clear coats.  The colour layer is applied to the primer and is typically very thin.  Its only purpose is to provide colour.  The clear coat is two to three times the thickness of the colour layer, adding to the appearance of paint depth and offering additional protection.  Manufacturers also use ultraviolet-light-blocking 

technology in their clear coat systems for protection against photo degeneration (sun fading).
Modern Isocyanate resins (clear coat) finishes are so good today that they lull people into thinking that vehicle paint has protection and shine when in reality there is not really much there, the clear coat that has a thickness of ~25.4 µ (micron). As a point of reference a sheet of copy paper is 89 µ

A micron (µ) is a metric unit that equals one millionth of a meter, or 1/1000 of a millimetre. A micron is much smaller than a Mil. A human hair is about 2 Mil (50 µ) thick and individual bacteria are 0.1 mil (2.5µ) in size. There are 25.4 millimeters in an inch and a micron is 1/1000 of a millimetre.

Using the micron (metric) measurement system gives you a much better idea of paint thickness as the numbers used are so much smaller. Most detailers are or should be aware of how thin clear coat paint is and it puzzles me why people over-polish paint causing it to fail prematurely

Abrasive Polishing
Polishing alleviates a myriad of paint surface problems. But use abrasive polishes wisely to maintain paint condition and to resolve surface damage problems. But know when to seek alternative methods of damage control and avoid over polishing with harsh, abrasive polishes.

There are two considerations; how much clear coat and how much ultra violet protection can be removed, they are not interchangeable. The following are the maximum allowable clear coat reductions the major USA car manufacturers will allow before the paint warranty becomes void; 0.3 Mil (7.5 µ)

Order of Magnitude (~ Thickness)
·        Standard printer copy paper 7.5 µ (0. 3 Mil) 
·        A standard sandwich bag 28µ(1.1 Mil)
·        Dollar ($1)  bill 73.5µ(2.9 Mil)

The 0.2 Mil (0.5 µ) is the maximum paint that they are allowed to remove on the assembly line at the factory during their paint sanding and polishing process to remove dirt nibs. This number is based on testing carried out at both General Motors (GM) and Chrysler testing centres.

Wet-sanding, compounding and polishing the amount of paint removed with a mild abrasive was ~ 0.1 mil (0.25 µ) this does not mean that the clear coat will fail if you remove 0.5 Mil (12µ)

There are many factors involved and each car plant may have a unique paint system that is designed for their specific needs and the thickness varies from one plant to another so there is no way to make such generalizations. One thing is for sure that if you keep removing clear coat, at some point you will experience strikethrough

The clear coat provides gloss plus physical protection from the elements, including ultraviolet (UV) radiation, which is in the upper level of a cured clear coat. Most car manufacturers will only allow ~ 25% of the clear-coat thickness to be removed without voiding the paint warranty and long-term durability problems becoming an issue. 

That means that if you started off with 50µ of clear coat (this will vary by vehicle manufacturer) you would only be able to remove <12µ without voiding the paint warranty and possibly having a re-paint.

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. Note:  25.4 µ (micron) = 1 Mil

Using a medium abrasive polish and a rotary polisher will remove approximately 2.5 - 3µ (0. 1 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)

               PPG’s CeramiClear clear coat is the first automotive clear coat to use nano particle technology in the final coating applied to car bodies, protecting the colour coat while providing a durable, glossy appearance. With the help of the nano-technology developed at the beginning of the 1980s, scientists have been able to alter the molecular structure of the binding agent and integrate tiny, microscopic ceramic particles. These each have a diameter of less than 20 nanometers, which makes them tens of thousands times thinner than a human hair.

During the electrostatic paint application process, it is sprayed just like a Melamine or Silane 2K clear; the key is what happens during the cross linking or curing of the clear. The hard "ceramic" particles rise to the top, just as the ultra violet (UV) inhibitors do, and concentrate there and the binding agent particles float around freely at first in the liquid paint.

The clear coat is the coating layer that forms the last interface to the environment.  It carries the biggest part of the technological performance and must be able to resist ultra violet radiation, environmental etch, bird droppings, car wash machines and other outside influences.

Be cognizant that clear coat thickness and composition will vary in accordance with the OEM assembly plant, paint specification, paint type (solvent or waterborne) and paint supplier and any additives used i.e. ultra violet stabilizers, Isocyanate hardener and catalysts

Base Coat Clear Coat – two stage paint; base (colour) coat and clear coat were adopted as an automotive industry standard in 19982, clear coat paint was originally used to protect metallic paints that are subject to oxidation and provide depth of colour. BC_CC paint systems do not oxidize in the same way as single stage paint does, but they are subject to clear coat failure. They are applied over the primer surfacer and covered by the clear coat layer to protect it from the environment.

There exist three main base coat systems in the paint shops of the automotive industry worldwide: medium solids (MS) high Solids (HS) Water-based (waterborne) (WB) paints are essentially low solids paints (up to 60% waterborne solvent), but they are legal because deionized water is used as the solvent, as opposed to volatile organic compounds (VOC).

The main purposes of the solvent are to adjust the curing properties and viscosity of the paint. It is volatile and does not become part of the paint film. It also controls flow and application properties, and affects the stability of the paint while in liquid state. Its main function is as the carrier for the non volatile components

Density (or specific weight); different materials usually have different densities, so density is an important concept as less dense fluids float on more dense fluids if they do not mix, causing it to rise to the top  (we have Archimedes to thank for this discovery)

 If the average density of an object is less than that of water, which is 1.0 g/ml, it will float in and if its density is higher than water's it will sink. Most organic solvents have a lower density ~0. 8 g/ml than water, which means they are lighter and will form a separate layer on top of water.

Benzotriazole is fairly water-soluble, not readily degradable and has limited sorption tendencies, which is used in some paint formulations to provide ultra violet protection. It has a specific gravity of 1.17 g/ml, which is heavier than water (0.98 g/ml) and much heavier than solvent (0.80 g/ml)

There is ultra violet (UV) protection all the way through the paint,  vehicle manufacturers also add ultra violet protection to the base coat to minimize the transfer due to density,  the majority of it migrates to the top as the paint cross-links,  along with the thinner solvents and particulates, the paint is also somewhat softer below this level.  The amount of migration will vary with the formulation of the paint, and which ultra violet protection chemical is used.  

Therefore removing clear coat ultra violet protection is not a linear process; by removing a small percentage of the clear coat paint tends to remove a larger percentage of the ultra violet (UV) inhibitors.

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 ultra violet inhibitors).

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 ultra violet protection, its long-term durability and / or the paint warranty

Photo degradation

[: decomposition of a compound by radiant energy] a common reaction is oxidation.

Today’s water-based products have a number of obvious environmental benefits, but some are more susceptible to photo degradation (fading) over time, a significant drawback. In addition, because of ozone depletion, higher levels of solar ultra violet (UV) radiation now reach the surface of the earth. This further contributes to the rate of fading.

Polymers use in auto paint, plastics and vinyl, where they are routinely exposed to sunlight; the UV radiation adversely the mechanical properties of these materials, often causing structural failure, which limits their useful life.

Paint Thickness

A paint thickness reading of > 100 µ (Microns) is reasonably safe for polishing.  80-90 µ, I wouldn't use anything stronger than >2000 grit polish, 70-80 µ  >2500, 70 µ use a glaze. The readings tend to vary from panel to panel and are thinner towards the panel edges and any seams.

·        200µ + can be expected on older cars that have been hand painted or a re-painted vehicle
·        100 – 200µ - average paint thickness
·        80 – 100 µ - thin paint
·      > 80 µ  - very thin paint

Paint Removed by Polish or Compound

Using a medium abrasive polish and a rotary polisher will remove approximately 2.5 - 3µ (0. 1 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 and etc that may affect the amount of paint and ultra violet protection removed

If you have reservations about the amount of paint surface removed or the amount of paint 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 / or UV protection, if so you’ll have to ‘live’ with the imperfection
Paint thickness will often depend upon the OEM paint specification, which can vary by vehicle assembly plant. 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

Order of Magnitude (Thickness)
·        Standard printer copy paper 76µ (3 Mil) thick.
·        A standard sandwich bag 28µ(1.1 Mil)
·        Dollar ($1)  bill 73.5µ(2.9 Mil)

These numbers are offered as a guide only, as there are too many variables to provide any more than an approximation.

1.      The elongation (elasticity) of paint enables it to move in tandem with the metal as it expands and contracts due to environmental temperature fluctuations; for this reason note the paint temperature when taking readings as they can vary in accordance to the surface temperature.
Measure your paint thickness in a very cold environment, then measure it when the paint surface is hot to the touch, you may find it varies by as much as a 2µ(microns)

Paint Insurance

The newer coatings available like synthetic polymers are  a cross-linking thermoplastic, its cross-linking process attaches the polymer with covalent bond that becomes part of the surface of the material it is attached to, which in effect becomes a secondary protection for the clear coat, in fact a relatively inexpensive (when compared to repainting) renewable  sacrificial coating.

Silica (AQuartz) or reactive resin hydrophobic coatings (OPT Opti-Coat™); think paint sealant that has greater durability and scratch resistance (9H) something that also provides a self-cleaning protection, with a durability on a timescale measured in years rather than months, these coatings add a measurable protection of 2-3 µ microns to the clear coat.

Opti-Coat™ is not a nano particle; it is rather a pre-polymer that cross links and forms a continuous film on the surfaces it is applied to, similar to a single component isocyanate that forms a clear coat finish. It is very resistant to alkaline car wash concentrates as used by car wash spas and tunnel wash companies

The coating is very low maintenance and requires cleaning less often than conventional paint protection products. Provided the surface is kept free of abrasive grime, bird excrement or other acids, the coating should last for around two years. Coating longevity will be improved if the paint surface is cleaned on a regular basis, and only with either normal pH car care concentrate shampoo or a citrus degreaser.

After Care

To enable a vehicle to maintain its value original paint that is in good condition is an asset. People are keeping their vehicles an average of nearly nine years. Making you client aware of how to wash and dry a paint surface while inflicting the least amount of damage will help to avoid the need to overly polish the clear coat to remove scratches and the subsequent loss of both clear coat and ultra violet paint protection.

The main point of this article is to inform detailer that there is a very limited amount of clear coat and to keep them from over polishing and unnecessarily removing their clear coat and ultra violet (UV) protection.

Providing this kind of value added-value services will enhance your reputation and enable you to become the source for both ethical service and high quality work. As with the successful sale of any product, educating the customer is the key.


1.      UV Protection and Coatings for Plastics in the Automobile Industry  - Paint & Coatings Industry (PCI) -

2.      Protecting UV-absorbing Clear Coats from Sunburn," Polymers Paint Colour Journal, February 2000


        1, Distribution of Stabilizers in Multi-Layer-Coatings and Plastic Coatings - 3rd International                 Coatings for Plastic Symposium, Troy, MI, June 2000.

2, Potential Reasons for Yellowing of Coatings over Plastic Substrates -  4th International Coatings for Plastic Symposium, Troy, MI, June 2000

3, Protecting UV-absorbing Clear Coats from Sunburn -  Polymers Paint Colour Journal, February 2000


1.        The Biology Project, Department of Biochemistry and Covalent (molecular) Biophysics
2.        The University of Arizona, Revised: January 28, 2003
3.        The Vinyl Institute Information
4.        The Royal Society of Chemistry; Cambridge, 1995 Silicon-Containing Polymers Richard,        G. Jones
5.        Royal Society of Chemistry (RSC) Library & Information Centre
6.        The Chemistry of Polyurethane Coatings  - Bayer publication
7.        Glossary of Chemical Terms - Faculty of Chemical Technology
8.        The Basics of Silicone Chemistry - Dow Corning
9.        Basic Concepts of Nanotechnology, History of Nano-Technology, News, Materials and            Potential Risks
10.     SpecialChem4 Polymers
11.     Macromolecular Chemistry and Physics  
12.     National Polymer Laboratories  Newsletter / Bulletins
13.     Sol-Gel Science - The Physics and Chemistry of Sol-Gel Processing by C. J. Brinker and         G. W. Scherer,
14.     Self-Healing Polymer Coatings, Cho, S.H.Cho, S.R. White, and P.V. Braun

Information resource

1.        The Center for the Polyurethanes Industry (CPI) of the American Chemistry Council
2.        Polymer Basics DoITPoMS - University of Cambridge
3.        Wikipedia Dictionary -
4.        Encyclopaedia Britannica Eleventh Edition -

I would like to think that these articles become an asset to anyone who is new to detailing and to professionals alike, as well as industry experts who seek to advance their knowledge.

Hopefully  the above article was informative. By having some understanding of the ‘What’ and ‘Why’ as well as the ‘How’ along with a little science to help you understand how the chemicals we use react, you can achieve the results you desire.

I would appreciate it if you would share this article as it helps other detailers further their knowledge.
Questions and/ or constructive comments are always appreciated.

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