Electronic Paint Thickness Gauge

BobbyG

BobbyG

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I understand the basic principal behind electronic paint thickness gauges but do have a few questions.


  • How accurate are they in real life usage?
  • How does it measure only one layer of paint?
  • What happens if the surface was repainted and could have several coats?
  • Do they work with fiberglass, carbon fiber, sheet molded compounds?
 
BobbyG said:
I understand the basic principal behind electronic paint thickness gauges but do have a few questions.


  • How accurate are they in real life usage?
  • How does it measure only one layer of paint?
  • What happens if the surface was repainted and could have several coats?
  • Do they work with fiberglass, carbon fiber, sheet molded compounds?
Click to expand...

By the questions I would say you need to look into them more.

Accuracy: very, much more than you need it to be, and much beyond what a human is able to repeat. Not an issue, all guages are decent and well beyond the detailer's scope of use.

Layers of paint: who said they measure only one layer? There are 3 models that measure from only ferrite containing alloys (steels and of course iron), another that measures alloys of all metals (aluminum panels for example), and the top model that measures on any surface. The first two are based on measuring the magnetic force and determining how thick of a non-conductuve coating is covering the substrate. In our case this coating is paint. The last type measures sonic resonance (ultrasound) instead of magnetic forces, thus its ability to measure on non-conductive substrates.

Thus if the panel has been repainted a paint thickness guage will measure how thick the resulting coating of paint is regardless of how many coats it has.

Prices vary. From around $75 for a Harbor Freight cheapo to the $2700 Defasko 200 advanced (the most advanced ultrasound guage that does individual layers or type of coating, ie base, clear, to some degree primer).
 
* How accurate are they in real life usage?


For the deflsko one AG has
defelsko-specs.jpg


It will b e plus or minus .1 mil plus 3%. This tolerance will go up and down depending on the PTG you get.


* How does it measure only one layer of paint?

All metal ones only measure total paint thickness, meaning from the bare metal to the top of the clear. Only ones made for plastics using sonar will do individual layers.


* What happens if the surface was repainted and could have several coats?

Then it will show the total thickness (on metal panels), of all layers of paint/primer/rust coating.

* Do they work with fiberglass, carbon fiber, sheet molded compounds?

Very few do, and ones that do are over $1-2k and use ultrasound.
 
Ptg-6000 and ptg-200 what you need to measure over anything.

Exotic Auto Detail via tapatalk
 
jlb85 said:
From around $75 for a Harbor Freight cheapo
Click to expand...

$75? I paid $6 for my HF coating gauge.

Funny part is I found that the Cen-Tech model they sell is being sold under another brand elsewhere for $200+

Im the MAN

Regardless, I hardly use it unless I've got a huge amount of sanding to do.
 
If you want one, make sure it does fiberglass, if you want to wet sand a corvettes...
 
I am still very glad that I bought the Harbor Freight "cheapo", even though I got it before it was discontinued and paid full price. Which was less than 60$ Unfortunately, it is now discontinued and there is no new model at Harbor Freight.

And I do agree that it may not give you an absolutely accurate measure of thickness. However, it will give you a "close enough" measurement. At least close enough to know when the surface you may be considering working on is already thin. Plus it will give you a very accurate measurement of how much build you may be removing in the course of your work.

But here is my test of it from years ago.


http://www.autogeekonline.net/forum...cheapo-harbor-freight-first-test-results.html
 
oldmodman said:
I am still very glad that I bought the Harbor Freight "cheapo", even though I got it before it was discontinued and paid full price. Which was less than 60$ Unfortunately, it is now discontinued and there is no new model at Harbor Freight.

And I do agree that it may not give you an absolutely accurate measure of thickness. However, it will give you a "close enough" measurement. At least close enough to know when the surface you may be considering working on is already thin. Plus it will give you a very accurate measurement of how much build you may be removing in the course of your work.

But here is my test of it from years ago.


http://www.autogeekonline.net/forum...cheapo-harbor-freight-first-test-results.html
Click to expand...

I think I read that thread before buying mine! Thanks! A good read indeed, and I agree with your conclusions and how you were using the tool :xyxthumbs:
 
agpatel said:
* How accurate are they in real life usage?


For the deflsko one AG has
defelsko-specs.jpg


It will b e plus or minus .1 mil plus 3%. This tolerance will go up and down depending on the PTG you get.


* How does it measure only one layer of paint?

All metal ones only measure total paint thickness, meaning from the bare metal to the top of the clear. Only ones made for plastics using sonar will do individual layers.


* What happens if the surface was repainted and could have several coats?

Then it will show the total thickness (on metal panels), of all layers of paint/primer/rust coating.

* Do they work with fiberglass, carbon fiber, sheet molded compounds?

Very few do, and ones that do are over $1-2k and use ultrasound.
Click to expand...


Good reply! The precision is even better than I remembered it. :xyxthumbs:
 
Thanks for the replies!

I think a paint thickness gauge does have it's place and I understand it's intended purpose but one question still keeps me scratching my head.

In general most finishes today are color-coat / clear-coat. Paint thicknesses today are scary thin and if anyone goes too far then it's time to head to the paint shop, which is very expensive.

Most is not all of our work is performed on the top coat or clear-coat. Knowing the thickness of the clear-coat is critically important in determining whether or not wet sanding or heavy compounding can be performed to effectivle remove a defect that has not broken through to the color-coat or deeper.

If these paint thickness gauges can only tell the total thickness of the paint film then what's the sense of spending what could be a large sum of money on them if the can't discern between layers?
 
You can guess the rage of the clear thickness from the base thickness, you clear can be anywhere from 30-40% of the total thickness of the paint. You can also take paint reading from door jamb seams, trunks seems as those areas will have thinner coats of clear and paint and you can kind of guess the clear thickness. Also send a red flag up if you hit a spot that is really high you know it is repainted and go slow there.

You can spend the high money and get one that can show clear layer but it is not needed as with a little math, picking the right spots, and sense of how cars are painted you can tell when you are getting too low to polish a car.

Like anything it is just another tool to provide the detailer with more information to help them decide what the best plan of attack is.
 
about 3-4 years ago I was searching for one, I found an ETG 2 on Ebay that a gentlemen was was a paint rep for DuPont was retiring and selling his. I got a pretty good deal on it, I think I paid 300 bucks for it. It measures steel/metal and aluminum.

Anyways, I've learned to what standard typical measurements are, generally on Fords/GM's later model vehicles, an average would be 4-6 mils, if it gets much below 4, I tend to really take caution when buffing in those areas. I take a measurements on a car I am not familiar with to see if it has any danger areas. I also like to use the gauge as a reference, checking and area before, during and after to see how much paint I am removing as well, but the problem can be, if you don't measure the exact location you checked before you started buffing then your reading will not be accurate due to the paint thickness being a little different from place to place.

I'm glad I got mine, gives me a little piece of mind on doing paint corrections.

Tom
 
Just like agpatel and Tom state, knowing some information is better than not knowing it, as long as the user understands the tools limitations. Even with a PTG tracking progress you can go through paint! Edges, corners, low spots and even worse high spots in the sheet metal can be passed over when inspecting or measuring and become more of a risk if readings show good paint health. So again, both sides have their advantages.

But a PTG without detailing forums would not be such a powerfully tool! As mentioned above, general guidelines on paint thickness on specific cars can be found relatively easily by searching here or on other forums. With this info and the PTG it is easy make a much better map to follow.
 
Does anyone know on average what a body shop would charge to give you some thickness readings? If it is comparable to buying a gauge or not.?. Just thinking if you were dealing with an older composite body and didn't want to drop a grand to test the paint and cover your butt with working on the paint. Thanks especially if anyone knows this for the Virginia Beach/Hampton Roads, Va area.
 
I know if I am asking this question then I should look into buying a gauge. But can anyone tell about how much thickness on average comes off when compounding with a DA and strong cutting pad?
 
Really only needed when you are wet sanding..but here goes..

Using a paint thickness gauge gives a professional detailer credibility and also acts as an insurance against ‘break-though’ of a clear coat, which would entail a re-paint and I suspect a very irate customer. Original paint has a better resale value than a re-painted vehicle, plus they will lose the use of their vehicle for some days. The ideal setup would be a DFT Combo for the metals and a PosiTector 200 B/Adv for the composites

Using a medium abrasive polish and a rotary polisher will remove approximately 0. 1 Mil (3µ ) Range 0.8 – 1.1 Mil (20 – 28 µ) from the paint surface (typically 4 passes at 1500-1800 RPM) but there are many variables such as the abrasive grade of the polish or compound and speed and pressure used that may affect the paint removed) These numbers should be checked with a paint thickness gauge (PTG) There comes a point when you must judge wither removing a scratch will compromise the clear coat and if so you’ll have to ‘live’ with the imperfection.

A paint thickness reading of 4 Mil < ( 100 µ (Microns) is reasonably safe for polishing. 3 – 3.5 Mil ( 80-90 µ) I wouldn't use anything stronger than > 2000 grit polish, 2.75 – 3.0 Mil (70-80 µ) > 2500 grit polish and under 2.75 Mil (70 µ) use a glaze.

If you have reservations about the amount of paint surface removed or the amount of paint coating remaining the use of a paint thickness gauge (PTG) is arbitrary

• 200µ + can be expected on older cars that have been hand painted or a re-painted vehicle
• 100 – 200µ 4 – 8 mil - normal paint thickness
• 80 – 100 µ - 3 – 4 mils, thin paint
• 80 µ < - less than 3 mil, very thin paint

For an old corvette like mine you need a different gauge, before you wet sand it...
 
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