Clear Coat and UV Protection Removal

Modern clear coat paint 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. One (µ) micron is roughly 1/80th of the thickness of a human hair. 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

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; Chrysler- 0.5 Mil (12µ) Ford – 0.3 Mil (7.5 µ) GM – 0.5 Mil (12µ)  (Source - Automotive International)

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 (Note: this may vary by vehicle mfg).

            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 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. 

 Water-based (waterborne) (WB) paints are essentially low solids paints (up to 60% waterborne solvent), but they are legal because de-ionized 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 (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 it’s 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.

There is ultra violet (UV) protection all the way through the paint, but the majority of it migrates to the top as the paint of cross-links along with the thinner solvents and particulates, the paint is also less dense (softer) below this level.  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

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 grit polish and under 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

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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

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

Notes:

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.

2.      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. 


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.