Question about microns of paint

[efnfast]

I was able to measure my paint today and found that it has (roughly) between 30 and 40 microns of clear, and between 350 and 400microns of basecoat.



Any ideas how these numbers stack up against production paint jobs? For example, twice the amount of clear you'd normally find, and twice the basecoat? I see averages of around 100-130, which I've always assumed are clear+base combined together, but figured I'd ask to make certain.

 

[Scottwax]

I was not aware of paint thickness gauges that can differentiate between types of paint on a car. Typically though, the color coat is very thin since you have the clear coat to protect it.

 

[efnfast]

It was a Positector that gave several readings, like this one

If it matters it was a fiberglass car - my friend said it could differentiate between the base layer and the clear.



I was just curious of others' experiences on here - probably limited because those fiberglass PTGs are pretty bloody expensive.

 

[Setec Astronomy]

Sorry I don't have this in microns, a typical factory paint job is about 4-6 mils thick. You've got ecoat, primer, color, and clear. The clear is 1.5-2, making it the thickest portion.



EDIT: There's a cross-section on this page: http://www.autopia.org/forum/guide-detailing/80225-polishing-paint-perfection.html . Here's another that talks about thicknesses: "Electronic Paint thickness gages- what they are and why you need*them" - Auto Detailing Articles and Tips by Kevin Farrell - Comprehensive Resources for Professional Auto Detailing Business Owners and the Automotive Detail Industry



Here you go, in microns: paint



EDIT EDIT: Circular/ Rotary Polishing Guide: remove swirls, scratches, & oxidation with a rotary polisher. foam pads, backing plate, lake country, professional, ...still can't find the one I was really looking for

 

[gmblack3]

I was able to measure my paint today and found that it has (roughly) between 30 and 40 microns of clear, and between 350 and 400microns of basecoat.



Any ideas how these numbers stack up against production paint jobs? For example, twice the amount of clear you'd normally find, and twice the basecoat? I see averages of around 100-130, which I've always assumed are clear+base combined together, but figured I'd ask to make certain.

I too have an advanced 200 PTG.



On a 08 vette in Crystal Red Metallic.



Total thickness on the hood was 5.0 mils or 127 microns.



Base was 1.5 mils or 38.1 microns.



Clear was 3.5 mils or 88.9 microns.



On a few different plastic bumpers, I have found approx the same. The base is usually 30-35% and the clear is usually 65-70 % of the total thickness.

 

[MarcHarris]

Speaking to Defelsko directly, as well as Elcometer/Highline directly, the are many issues with these ultrasonic coating thickness guages.

First off, they were never designed for use on automotive paint. To be used on automotive paint can therefor lead to big drops in accuracy. If you think about how sonic waves move (as they move over distance, they spread) you'll realize the problem of trying to take readings off of a curved surface, you'll at least understand in part.



A Defelsko representative told me that while it can still be used, one issue likely to come up is you won't get readings aside from the clear-coat and everything else. In short: you'll get a reading of the clear-coat, but the base coat, primer-sealer, primer-surfacer, and E-coat/self-etching primer will likely be grouped together as there isn't a big enough difference in the density in those layers for the tool to tell a difference in them.



This will help to show you that even though it seemed to read differently, you're clear-coat is, like others pointed out, still going to be the thickest layer. Everything other than the clear was just lumped together.



To other pro's reading this, take into account that with a drop-off in accuracy, it's still better to have 80% accuracy and have an idea then to go totally blind.

-Marc

 

[Setec Astronomy]

Speaking to Defelsko directly, as well as Elcometer/Highline directly, the are many issues with these ultrasonic coating thickness guages.

First off, they were never designed for use on automotive paint. To be used on automotive paint can therefor lead to big drops in accuracy. If you think about how sonic waves move (as they move over distance, they spread) you'll realize the problem of trying to take readings off of a curved surface, you'll at least understand in part.

Are these ultrasonic, rather than eddy current? Forget automotive, eddy current testers have problems with curved surfaces, or any surface different than what you calibrate on. All of that has to be factored into how you interpret the results.

 

[MarcHarris]

Good question Setec, and I believe all coating thickness readers that are meant for wood/composite materials are ultrasonic so they can read on things other than metal

 

[Accumulator]

Oh you guys are killing me with all this talk about differentiating ETGs :drool:

 

[Street5927]

1 mil is approximately 25.4 microns. A new car has a basecoat of approximately 4.0 mils (101.6 microns) to 6.0 mils (152.4 microns). The clear is approximately 1.5 mils (38.1 microns) to 2.2 mils (55.8 microns). For a new car, you should see variations from 5.5 mils (139 microns) to 8.2 mils (208.2 microns). You should remove NO MORE than 25% of the clear or .375 mils (9.5 microns). I always go on the basis of the lowest possible amount, that being 5.5 mils (139 microns), less the 25% clear or 129 microns, you know that you are very close to polishing/sanding through the clear. In your case, it seems as though your clear is thicker than your basecoat, which makes me wonder if your machine is working properly. As said before, I don't know of any paint guages that are able to differentiate between the clear and base.



On the other hand, your machine is converting mils to microns correctly. If you take your mils and multiply by 25.4, you will get micron readings.



1.5mils (base) x 25.4 = 38.1 microns

3.5mils (clear) x 25.4 = 88.9 microns



If you have a guage that only measures in mils, just take your mil reading and multiply by 25.4 and it will give you a micron reading. Hope this helps

 

[efnfast]

In your case, it seems as though your clear is thicker than your basecoat, which makes me wonder if your machine is working properly. As said before, I don't know of any paint guages that are able to differentiate between the clear and base.

So with the positector 200 if there are 3 readings on the lefthand side of the screen say, for example, say,



1 - 45



2 - 400



3 - (blank)



How would you interpret that?



For what it's worth, it's a fiberglass car and all parts were handsprayed (i.e., this is not a production paint job). The paint is definately thick because if, for example, I lift up the hood before it was painted, and after, it's noticeably heavier after paint.

 

[Street5927]

So with the positector 200 if there are 3 readings on the lefthand side of the screen say, for example, say,



1 - 45



2 - 400



3 - (blank)



How would you interpret that?



For what it's worth, it's a fiberglass car and all parts were handsprayed (i.e., this is not a production paint job). The paint is definately thick because if, for example, I lift up the hood before it was painted, and after, it's noticeably heavier after paint.

I would check the manual to see what the readings are, however, I think it is unusual to have thicker clear than base.

 

[the other pc]

Are these ultrasonic, rather than eddy current? ....

Yes, the PosiTector 200 and 100 series Coating Thickness Gages are ultrasonic.

...A Defelsko representative told me that while it can still be used, one issue likely to come up is you won't get readings aside from the clear-coat and everything else. ...

I believe what he told you is an oversimplification.

.... In short: you'll get a reading of the clear-coat, but the base coat, primer-sealer, primer-surfacer, and E-coat/self-etching primer will likely be grouped together as there isn't a big enough difference in the density in those layers for the tool to tell a difference in them.



This will help to show you that even though it seemed to read differently, you're clear-coat is, like others pointed out, still going to be the thickest layer. Everything other than the clear was just lumped together....

This may be the core of that oversimplification.



It is certainly true that an ultrasonic gage may or may not be able to differentiate between layers. It depends on how much of an “echo” is returned from the material boundary and the sensitivity of the detection method.



The quality of the echo is dependent on the how closely the materials are matched in “characteristic impedance,” which is a function of a material’s density and the speed of wave travel through it. (When the material is air, it may be called “acoustic impedance.”)



The more closely two materials’ impedances match, the less echo, because sound propagates through them in the same way. The greater the difference between their impedances, the larger the echo.



Since different layers of an automotive coating system can have rather similar chemical/physical composition there may sometimes be little difference between two layers’ impedances. So there may be little echo. But it’s really dependent on the specific combination.



There’s no reason an ultrasonic won’t work on metal substrates. They have their own characteristic impedance like any other material. In fact, ultrasonic measurement is often used for checking pipe wall thickness. But I don’t doubt that magnetic and eddy current techniques are more accurate on metal substrates.



Any sort of wave propagation has some equivalent to characteristic impedance. In the field radio wave transmission it’s also called characteristic impedance. In the field of optics and light transmission, it’s called index of refraction.



In open space, the radio wave equivalent of what the PosiTector does is called RADAR. For enclosed cables, the radio wave equivalent is called a Time Domain Reflectometer. The equivalent machine for fiber optic cables is also called a Time Domain Reflectometer. The equivalent in water is called SONAR.







pc.

 

[efnfast]

I would check the manual to see what the readings are, however, I think it is unusual to have thicker clear than base.

My friend told me that the first reading on it is the clear, which would make sense since that's the first layer. (I just borrowed it from him for a few minutes, he's the expert, not me, heh, just wanted to see what others were getting for various readings)



Maybe somebody whose used a Positector 200 religiously could chime in because I'm starting to get really confused, heh.



Again, this isn't a production car (entire car is fiberglass), or a production paint job - hand sprayed with 4coats of clear FWIW.

 

[Showroom Shine]

This is some very Good info on the gauges and paint mils and microns. Real techy stuff. But never the less useful. So how many of you PRO'S are using the guage?Do you have to have it for every car?

 

[MarcHarris]

Showroomshine - We use one on any car that will have paint correction performed. It's always good to get an idea of where there may be any problem areas.





Thank you to The Other PC. Very good in-depth explanation. The representative didn't seems to over-simplify, rather I'm trying to paraphrase for the sake of a quicker post. The information you posted will be of a huge help to anyone who would like in-depth info onto how these ultrasonic meters work.



To others: Your clear-coat is the thickest layer. It sprays on thicker, doesn't easily lay flat, and gives off seemingly stronger VOC's compared to spraying base-coat. Just because your Coating thickness meter groups the base-coat+E-coat together (factory) or base-coat+sealer+primer-surfacer+self-etching primer together (aftermarket respray) doesn't mean the clear is thinner than the base. As The Other PC pointed out, it's hard for the PTG to differentiate in the layers under the clear because of sensitivity settings from the factory.

 

[efnfast]

To others: Your clear-coat is the thickest layer. It sprays on thicker, doesn't easily lay flat, and gives off seemingly stronger VOC's compared to spraying base-coat. Just because your Coating thickness meter groups the base-coat+E-coat together (factory) or base-coat+sealer+primer-surfacer+self-etching primer together (aftermarket respray) doesn't mean the clear is thinner than the base. As The Other PC pointed out, it's hard for the PTG to differentiate in the layers under the clear because of sensitivity settings from the factory.

So from what I wrote above, would you say I have around 40microns of clear, or more?

 

[MarcHarris]

So from what I wrote above, would you say I have around 40microns of clear, or more?

I would believe this to be correct, and doesn't seem unusually thick nor thin. Some paints will have more clear / thicker clear than others depending on many factors of course, but averaging 40 microns for your clear seems about right.