How to use a Paint Thickness Gauge (PTG)

hernandez.art13

hernandez.art13

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Hello everybody, I left the title really general in case others searched and needed information in the long run. I got a quick run through, through my estimator uncle on how to use a PTG. He was pretty impressed with the one I have opposed to the one he uses.

He said they call the readings Mils at the shop he works at.

View attachment 19817
View attachment 19810
^Repainted Hood
View attachment 19811
^Blended Fender
View attachment 19812
^Side View Mirror
View attachment 19813
View attachment 19814
^Roof
View attachment 19815
^trunk
View attachment 19816
^Spoiler

Extremely neglected Rx7
View attachment 19818
View attachment 19819
^Fender
View attachment 19820
^Hood
View attachment 19821
^Trunk

I am still learning and this thread is to further educate me and others on how to use a paint thickness gauge.

Thank You,
Art
 
Does it matter if a car is extremely dirty or have multiple layers of wax to get an accurate reading?
 
A "mil" is the term used in the films (including paint film) industry, and it's .001 or one-thousandth of an inch. You use this in referring to paint or coating thickness as well as films such as plastic bags, etc.

Multiple layers of wax aren't going to be thick enough to make any difference with the accuracy of your instrument, it would be a good idea to get any dirt off as that may have significant thickness or particulate and could hold the head off the surface.

You can see the repainted panels in your measurements, the ones with 10+ mils, vs. the 4-5 mils of the factory panels.
 
Search feature helps :

Mike.Phillips@Autogeek said:
What you're looking for when you measure the thickness of the paint on your car is uniform measurements. That is, measurements all withing a close range of one another from panel to panel and if you're lucky, over the entire car.

If you see a big change between readings on a single panel this would be a sign of potential risk or problems especially if you find thin paint surrounded by the norm readings. You should also look for signs of previous buffing work on panels with thinner paint, like lack of orange peel in the thin area but the orange peel kicks back in around the normal readings.

If you find thicker paint measurements around the normal readings this could be a sign of underlying bodywork from a repair.


There's a number of good reasons to use a Paint Thickness Gauge, I think I outline them in the second edition of my how-to book.

If I'm going to buff out a car, the primary reason I use a paint thickness gage is to help me make what I call, the "Go" or "No Go" decision. That is as a "Big Picture Indicator" as to where the paint is safe to work on or if there are areas to either avoid or tread lightly.

I was really glad I measured the paint thickness on Wayne's classic Hudson Hornet as it helped me to choose the path of using the least aggressive products to get the job done and the results still turned out great and there were no polishing related problems.

Wayne Carini 1954 Hudson Hornet Original Paint Restored by Mike Phillips


This is thin paint...

Thin_Hudson_Paint_002.jpg





:xyxthumbs:
Click to expand...
 
Setec Astronomy said:
A "mil" is the term used in the films (including paint film) industry, and it's .001 or one-thousandth of an inch. You use this in referring to paint or coating thickness as well as films such as plastic bags, etc.

Multiple layers of wax aren't going to be thick enough to make any difference with the accuracy of your instrument, it would be a good idea to get any dirt off as that may have significant thickness or particulate and could hold the head off the surface.

You can see the repainted panels in your measurements, the ones with 10+ mils, vs. the 4-5 mils of the factory panels.
Click to expand...

Thank You, I will give this area a nice wipe to see if there is a significant difference when I get home

View attachment 19824
 
I was using my PTG today on the AMX Mike Phillips and others wet sanded cut and buffed (see Helping in the Heartland), and I was getting readings from 23 mils all the way up to 44 mils!!
 
erichaley said:
I was using my PTG today on the AMX Mike Phillips and others wet sanded cut and buffed (see Helping in the Heartland), and I was getting readings from 23 mils all the way up to 44 mils!!
Click to expand...

I guess that's another story what you were doing working on that car, but apparently that guy sprayed a lot of clear.
 
Was doing reading and saw ZmcGovern's work on the BMW, what an awesome job he did.

Found no rust, dirt or wax prior to using the PTG btw.
 
If I told you...

I was actually there doing some paint correction on Wes' 99 BMW 528i wagon. To say the paint is rough is an understatement. Severely scratched, pitted, you name it. Did a test spot and, for as bad as it was, it turned out pretty damn nice!

You can see just how rough it was:
OxXxzqFBefDIW3C9rpgiZgbvdHFXLWBIa8PeSTyhlfc


And how it turned out:
tD35_TQJ5YDmU46d66j-tRv45986x6PXK9qlZDnn4xY


vtCe1E7Su3AwgjeIjFQsWZ23T8_D-x5_SJe1QPgvScI
 
So 120-150 is healthy paint? What happens if it goes below that?

The lowest I got on my car was the roof, where it read 100

And does anyone know at what no. CC failure happens? Or is a case by case basis?
 
erichaley said:
If I told you...

I was actually there doing some paint correction on Wes' 99 BMW 528i wagon. To say the paint is rough is an understatement. Severely scratched, pitted, you name it. Did a test spot and, for as bad as it was, it turned out pretty damn nice!

You can see just how rough it was:
OxXxzqFBefDIW3C9rpgiZgbvdHFXLWBIa8PeSTyhlfc


And how it turned out:
tD35_TQJ5YDmU46d66j-tRv45986x6PXK9qlZDnn4xY


vtCe1E7Su3AwgjeIjFQsWZ23T8_D-x5_SJe1QPgvScI
Click to expand...

^Mirror finish! Great job!
 
hernandez.art13 said:
So 120-150 is healthy paint? What happens if it goes below that?

The lowest I got on my car was the roof, where it read 100

And does anyone know at what no. CC failure happens? Or is a case by case basis?
Click to expand...

On my 2013 Honda Accord, I've found 100 mils to be about the lowest I am comfortable going. Signs of impending strike through occur at around 80, with full strike through not far behind. I'd say, in my case, that below 100 is seriously dangerous territory. One can't be willing to do serious paint correction on someone else's car unless they know what failure looks like on their own.

I'm comfortable in my mistakes as I've learned a great deal about what it takes to fix it and, more importantly, how to avoid it in the future.

I repainted part of this door and recleared the entire thing:

t-0r7HNvUvj9P_nF2JMb-tBh3bEyUk400xZkrGvepCI%2CpUXKRTBR7JsSkTDucZ9eVx11P4YdApPQeBZJauDN5SU


Using aerosol cans...
 
hernandez.art13 said:
So 120-150 is healthy paint? What happens if it goes below that?

The lowest I got on my car was the roof, where it read 100

And does anyone know at what no. CC failure happens? Or is a case by case basis?
Click to expand...

Paint readings are all totally dependent on the car you are working with... let's take a car with average readings of around 100 microns - you do not know if you have 10 microns of clear to work with or 50 microns of clear to work with. The PTG simply allows you to analyze areas of concern when you see particularly high or low readings, and gives you a chance to make a more educated decision than you could have made without a PTG.
*note: there are ultrasonic PTG's that allow you to read that actual thickness of each individual layer of material, however these are out of the range of most amateurs and weekend warriors.

Typically repaired or repainted areas will read higher than expected (compared to the rest of the vehicle).

When I was working on this Audi...

http://www.autogeekonline.net/forum...turned-into-proper-detailer-2004-audi-s4.html

... I found an area on the driver's side rear door that had readings in the 400-500 micron range. This car currently belongs to a close friend of mine, but it just so happens that I know the previous owner of the car too. I called him to see if he had any insight as to why I was getting the unusually high readings and he explained to me that there was a pretty good door dent that had to be filled and repainted in that area... makes sense. So because of the PTG I was able to determine that a repair had been done and I may need to pay extra attention to that area.

On the opposite side of things... when I was working on my wife's car (right after we bought it)...

http://www.autogeekonline.net/forum...ation-paint-correction-22ple-application.html

... I was getting readings that averaged 75-80 microns, which is pretty darn thin! This made me choose a different plan of action just to be safe, as I could assume that there was a lesser amount of clear coat on that particular car than what would be considered "average".

-Zach
 
zmcgovern45 said:
*note: there are ultrasonic PTG's that allow you to read that actual thickness of each individual layer of material, however these are out of the range of most amateurs and weekend warriors.
Click to expand...

AFAIK those PTG's only work on non-metallic substrates, which is great if you have a Corvette or just want to check bumpers.
 
If you have a beater car or test panels from junk yard to work on sand the CC until you just break through and take readings (a true reading #!). Measure the panel in a good area and subtract reading #1.

When working on a REAL car measure the trunk lid or verticle door jam because it will have less CC (reading #1). Then measure your panel and subtract reading #1. This will tell you the APROXIMATE amount of clear you have to work with.

Then apply common sense.
 
I don't have a PG yet, planning on getting one very soon.

What would you guys consider the minimum paint thickness to do the following steps:

1. Wetsanding a RIDS
2. Doing heavy compounding (Microfiber+M105)
3. Doing light compounding (Polishing Foam pad+M105)
4. Doing Standard polishing (Polishing foam pad+M205)
5. Doing Light polishing (Finishing pad+M205)

And how much paint can I expect to remove with each of these steps?
 
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