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Old 10-15-2014, 10:16 AM   #1
Surf City Garage
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Default Surf City Pro Tech Tip: How Polishing Impacts Clear Coat Thickness

Good Morning! My good friend Dylan, and also the Innovator of this line, and Director of Innovation for Surf City Garage, recently wrote this article. I thought it was both a great read as well as very educational. This post will be in a few pieces, so please, grab something to drink and/or a snack, sit back, relax, and enjoy!

__________________________________________________ ______________

For some guys this isn't new info, but I do see a lot of rookie polishers and casual detailers asking about this online so figured I'd put the info together.




"Does machine polishing remove clear coat?"

"How many times can I polish my car?"

"Can I polish my car too much and wear away the clear coat?"



There is a lot of info out there about how to use machines for polishing. A quick youtube search and you'll have hundreds of videos from amateurs and professionals outlining the process of removing clear coat scratches and swirl marks with any number of tools. The one thing few, if any of these videos addresses are the concerns that come after you've learned how to fix the paint. A casual reading in any forums detailing section reveals how little most people actually know about the limitations of polishing, how much material is removed with each correction, and feasibly how many times you could correct a paint job in a cars life. I've been shocked to read some people even claiming extreme things like polishing can only be done once or it ruins the clear coat, while others claim that polishing doesn't even remove clear coat to begin with.

This article is intended to arm you with the basic knowledge of paint thickness and how your paint correction process impacts your vehicles finish over time. Hopefully this info can be helpful to you as you care for your own vehicles or detail for others.

In order to understand coating thickness there are a few terms we first need to define and explain -
  • Clear Coat = pigment free paint that is applied as a top coat to automotive surfaces. Nearly 95% of all vehicles manufactured since the mid 1980s are clear coat paint jobs. Clear coats were adopted widely for their UV stability, oxidation resistance, and chemical resistance versus traditional lacquer type finishes.
  • Base Coat = pigmented paint applied prior to clear coat which gives a vehicle its outward color/appearance.
  • Mil = a unit of measure for the thickness of films, coatings, and other thin materials. 1 mil = 1/1000th (0.001) of an inch or or 0.0254 millimeters.
  • Micron = a unit of measure equivalent to 1/1000th (0.001) of a millimeter. Represented by the symbol:
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Old 10-15-2014, 10:16 AM   #2
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HOW MUCH PAINT IS ON A NEW CAR?
The amount of paint thickness on a car can vary greatly depending on the make/model, it can even vary from panel to panel on the same car. On average most cars will arrive from the factory with somewhere around 5 to 6 mil of total coating thickness. This is the total amount of paint (base and clear) on the panels.

You can verify this or get a more precise measurement for your exact car by using a paint thickness gauge. They can be found for as little as $150 online, but be aware that lower cost meters will only register thickness readings on steel panels - so aluminum, plastic, carbon fiber, fiber glass, and similar surfaces won't be able to be read. Meters that can read these other (non-ferrous) materials tend to be much more expensive.

Now, of that total 5 to 6 mil surface coating my experience, as well as corroborating info from other respected sources puts the portion of that total coating attributed to clear coat at around 1.5 - 2 mil of the total. If we assume the high sides on the averages that gives us the following breakdown of the paint on the average car when new:





So exactly how thin is 50.8 microns of clear coat? To put it into perspective the average piece of copy paper comes in at a thickness of around 100 microns, so your cars clear coat is just about exactly half the thickness of a sheet of paper! Seems awfully thin right? Easy to see how someone could be intimidated by the prospect of rubbing abrasive polishes and pads on something so thin, but as you'll see in the next section the amounts of material removed in correction are actually a small percentage of the total.

HOW MUCH CLEAR COAT DOES POLISHING REMOVE?
Just as the depth of scratch or swirl mark you're working to remove can vary so will the amount of clear coat you'll need to 'remove' in order to correct it. Most imperfections will be removed somewhere in the 1 to 4 range. Average swirls and light imperfections will fall in the 1-2 range and deeper RIDS and scratches will fall in the 3-4 range in terms of how much surface will need to be removed.

Knowing that a full correction of even a heavily swirled finish will reduce the clear coat 4 we can start to put together some rough numbers of how paint correction will impact your car over time and potentially how many times you can polish a finish before you would be at a point to be concerned about reducing it too far.

Those light, in between, touch-up corrections are typically going to reduce clear coat thickness in the range of 0.5 to 1 so it becomes increasingly important over time to focus on swirl prevention and minimizing the damage introduced in your washing/cleaning processes. The less you have to correct, the less clear needs to be removed.

So you can see that because of how relatively thin factory clear coat is starting with the least aggressive approach to correct the paint becomes very important. This isn't just in terms of conserving effort or product, but minimizing the amount of material you abrade from the surface. Why remove 4 when the defects you're attacking are only 1 deep?
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Old 10-15-2014, 10:16 AM   #3
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HOW MANY TIMES CAN YOU POLISH YOUR CAR?
Heres the good news - despite the seemingly razor thin application of clear on your car there is still an abundance of material to work with over the life of your car. Studies conducted in recent years show that the average length of ownership for a new car in the US is currently about 6-7 years and here is why thats relevant in a discussion about the thickness of clear coat:

Hypothetically you buy a new car and the paint has fairly common swirls from a lot porter washing it before you had a chance to tell them no. You get it home and perform a two step paint correction reducing the clear coat thickness by about 2-3 to remove the swirl marks installed by the dealer. So shortly after taking delivery your new car - which started with about 50.8 of clear coat now has about 48.8 remaining.

Because you take your detailing seriously you practice solid 2-bucket wash habits, you use quality car wash soap, and you use only the best drying towels to minimize the swirls you introduce to the surface. Like many shine junkies you keep a good coating of your favorite wax or sealant on the surface and you take excellent care of your car. Also, like anyone serious about their car care you do your touch-up corrections a couple times a year. Just a light polish to remove any swirls or other defects that may have occurred over the past 6 months.

If this pattern holds true you are maybe averaging the removal of 1-2 per year of ownership to keep that swirl free shine. If we assume an average of 1.5 per year that means your clear would still sit at 39.8 at year 6 or 38.3 at year 7 - the average length of ownership for most car owners in the US.
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Old 10-15-2014, 10:17 AM   #4
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HOW MUCH CLEAR CAN I SAFELY REMOVE?
As mentioned in one of the earlier sections, clear coat paints became popular in part due to their higher UV stability and resistance. Single stage paint jobs were prone to oxidation and fade - if you've ever seen an old red lacquer paint job that has turned to a chalky pink you can understand why a more stable, UV resistant paint system was needed. This ability to withstand UV rays comes from blockers mixed in with the clear coat when it is applied, but these blockers have a tendency to migrate to the upper portions of the clear - paint sinks and the blockers rise as the clear coat hardens.

While there are conflicting bits of information on this its generally accepted that the UV blockers reside in the upper 25%+/- of the clear coat. As such its recommended that clear coat removal be limited to no more than 25% of the total thickness, at least in order to preserve that UV stability.

Referencing our original example - 50.8 to start - removal of 25% would put the remaining clear around 38.1 and as luck would have it in our example 7 years of average care after one initial major correction would leave you with 38.3... 0.2 more than the recommended minimum to maintain the UV protection.

In the end this illustrates one very simple point - if you're already following good detailing processes, minimizing damage introduction wherever you can and sticking to the rule that you should always use the least aggressive method to get the job done, then DON'T CHANGE A THING! You're already doing everything the way you should be.

On the other hand, if you're one of those guys who skips the maintenance in favor of heavy corrections more frequently you may be flirting with disaster. It also is imperative for those who call detailing their profession to educate their customers on the limitations of correction and the importance of proper paint care in between corrections.



NOTE: Anyone looking for a decent paint gauge thats relatively inexpensive I have been using this model, purchased on Amazon for about $150 and for the price has been very good.

DT-156-Coating-Thickness-Tester

Just realize that this meter in particular only measures total coating thickness, and does not differentiate between base and clear, but it at least gives you something to gauge the reduction of the surface.
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Old 11-01-2014, 05:39 PM   #5
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This is really awesome and detailed information! This is always something I've wondered, and it's really nice to have exact figures on things like removing clear coat.
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