Messuring clearcoat with single paint gauge

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Charlieboy1

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Hi people
just wondering how people can measure and judge how much clear coat is on the car when using a normal paint depth gauge that has a whole reading and not like the expensive ones that read each layer.
I understand people start doing test spots starting with least aggressive combos etc but doesn’t explain
rough clear coat guide if that makes any sense
people have different ways of doing this but just wanted to know peoples views on this

Thank you
Charlie
 
I wondered the same thing and reasoned that a gauge is useless unless you spend the big bucks.
 
All an inexpensive paint gauge can give you is a rough idea of what's going on with a base coat/clear coat paint job. Most new cars seems to measure out around 5 mils of total paint thickness. Mike Phillips tells us that, new, we're looking at 2 mils of clear coat.

Clearcoats are thin

So if you're looking at a fairly new car that hasn't been resprayed then you can do a little math to give yourself a rough idea of what is going on. Outside of those parameters I don't rely on the gauge to tell me much.

Bill
 
The only way I’ve heard/read to get a rough estimate is to measure a panel and then measure a door jamb. Take those measurements and subtract the door jamb from the panel measurement.

The theory behind this is that (according to what I’ve read), the jambs won’t be clear coated whereas the exterior panels will be. All in an effort for car companies/manufacturers to save on build cost.
 
So you're saying that if I took a towel and some polish to a door jamb, the paint color would transfer to the towel (no clear coat)? I've never seen that happen.

Bill
 
DMiglio said:
The only way I’ve heard/read to get a rough estimate is to measure a panel and then measure a door jamb. Take those measurements and subtract the door jamb from the panel measurement.

The theory behind this is that (according to what I’ve read), the jambs won’t be clear coated whereas the exterior panels will be. All in an effort for car companies/manufacturers to save on build cost.
Click to expand...

You were correct up to where you stated that there was no clear coat on the door jambs. The clear coat on the door jambs are not as thick as on the body panels. This should give you a rough estimate of the amount of clear you have to work with. IMO you should not compound a car with less than 90 microns.
 
DMiglio said:
The only way I’ve heard/read to get a rough estimate is to measure a panel and then measure a door jamb. Take those measurements and subtract the door jamb from the panel measurement.

The theory behind this is that (according to what I’ve read), the jambs won’t be clear coated whereas the exterior panels will be. All in an effort for car companies/manufacturers to save on build cost.
Click to expand...

That is correct most of the time. There are exceptions. ie, I did a BMW X5 yesterday and the paint mesurements on the hood were in between 150 to 200 microns. I measured the door jamb and was getting 160-180 readings. So in a case like that, the door jamb mesurement is useless. Most of the time, the door jamb will give you reading much lower than the panel, in that case, you can be pretty sure that the diffence is actual clearcoat surplus.

When the readings are equal between the jamb and panel, I consider that about half that paint thickness is clearcoat and the other half is primer+basecoat. So on a reading of 150, I would consider the clear to be 75 microns thick. I really try never to remove more than 10 microns of clear if possible. And if the paint is really thin (say 100 microns or less) I would advise against any wet sanding or heavy compounding. You may not go through the clear but you might leave so little behind that it will fail prematurelly.
 
Awesome info! Thanks for responding guys, not only did I get a clearer understanding of what I had typed about the panel/door jambs, but hopefully too helped the OP and any others who read this.

Waelwell, reading your post made me realize just how wrong my post was... door jamb paint transfer never happened to me either.
 
Calendyr said:
That is correct most of the time. There are exceptions. ie, I did a BMW X5 yesterday and the paint mesurements on the hood were in between 150 to 200 microns. I measured the door jamb and was getting 160-180 readings. So in a case like that, the door jamb mesurement is useless. Most of the time, the door jamb will give you reading much lower than the panel, in that case, you can be pretty sure that the diffence is actual clearcoat surplus.

When the readings are equal between the jamb and panel, I consider that about half that paint thickness is clearcoat and the other half is primer+basecoat. So on a reading of 150, I would consider the clear to be 75 microns thick. I really try never to remove more than 10 microns of clear if possible. And if the paint is really thin (say 100 microns or less) I would advise against any wet sanding or heavy compounding. You may not go through the clear but you might leave so little behind that it will fail prematurelly.
Click to expand...


Thanks for the feedback yeah I always thought anything over say a little more than 100 was safe
just say you have panels that are resprayed how can you do that meathod I suppose it’s tricky right?
 
Calendyr said:
That is correct most of the time. There are exceptions. ie, I did a BMW X5 yesterday and the paint mesurements on the hood were in between 150 to 200 microns. I measured the door jamb and was getting 160-180 readings. So in a case like that, the door jamb mesurement is useless. Most of the time, the door jamb will give you reading much lower than the panel, in that case, you can be pretty sure that the diffence is actual clearcoat surplus.

When the readings are equal between the jamb and panel, I consider that about half that paint thickness is clearcoat and the other half is primer+basecoat. So on a reading of 150, I would consider the clear to be 75 microns thick. I really try never to remove more than 10 microns of clear if possible. And if the paint is really thin (say 100 microns or less) I would advise against any wet sanding or heavy compounding. You may not go through the clear but you might leave so little behind that it will fail prematurelly.
Click to expand...


Thanks for the feedback yeah I always thought anything over say a little more than 100 was safe
just say you have panels that are resprayed how can you do that meathod I suppose it’s tricky right?
 
First - I don't know anyone that has the very expensive gauge that reads all layers.

Even if you did have one, to properly use it would take HOURS.

While someone is using it I could have the car buffed out and be paid --> $$$ and then moving on in life.


If you read enough threads on this forum about PTGs - when I comment I say the same thing, in fact I should write an article on the topic. I use a PTG for 2 things,


  1. As a BIG PICTURE indicator
  2. Marketing



An accurate PTG will let you know relative paint thickness and this will let you know whether to compound or avoid compounding and stick with light duty products.

For marketing, you can use this tool to show a potential customer that you really know your craft. My guess is after you sticker shock the potential customer and they go somewhere else, the next guy will NOT have a PTG and this potential customer will at least see the difference between someone that knows his craft and has the tools to prove it and a detailer that may know is craft but does not have the tools to prove it.


:)
 
Mike Phillips said:
If you read enough threads on this forum about PTGs - when I comment I say the same thing, in fact I should write an article on the topic. I use a PTG for 2 things,


  1. As a BIG PICTURE indicator
  2. Marketing

An accurate PTG will let you know relative paint thickness and this will let you know whether to compound or avoid compounding and stick with light duty products.
Click to expand...


^^ This. I use a very cost effective gauge that I can PM You details around. Works great. Like Mike, I use it for the big picture and to show customers I know what I'm doing and looking for when using it. My main goal is to find areas that are repainted (which you can often find visually) and measure the thickness and consistancy of the spray on those panels and any subsequent panels that may have been blended.

The thickness itself is also very important as I've measured several cars that show only 2.5-3.5 mills total. SUPER Thin and without knowing that, I could very easily have done damage. It's also good to inform a customer if their car has been repainted, compounded heavily, etc.

When wet sanding out scratches, it's key too. Lots of reasons to use one and honestly, if I didn't have one, I wouldn't at all feel comfortable polishing a vehicle that I didn't personally know.
 
Charlieboy1 said:
Thanks for the feedback yeah I always thought anything over say a little more than 100 was safe
just say you have panels that are resprayed how can you do that meathod I suppose it’s tricky right?
Click to expand...

Repainted panels are usually easy to spot. First, the texture/orange peel will be different from the rest of the car in most cases. Second, the readings on that panel will will be different from the rest of the car. More often than not, there will be much thicker paint on that panel, sometimes as much as twice as the rest of the vehicle. So on repainted panels, you have to be cautious. You don't know if the painter simply left the original paint in place and painted over it, or if he stripped the panel to metal and started from the ground up. If he did paint over it, you basically have 5 or 6 layers of paint, so the top layer of clear coat might be thin even if the overall paint is thick. So no agressive wet sanding.

As a DA polisher user, I have no fear of compounding on thinner paint unless it's something crazy like 50 microns thick overalll. I have done tests over the last year and compounding doesn't remove that much paint with a DA. That is the reason a DA can't really remove any deep scratch and you need to wetsand.

With a rotary, I would be very cautious compounding a repainted panel unless you have some way of knowing the clear coat is not thin.
 
Just to ask....


I can wrap my mind around mils.

I can hold a post-it note between my thumb and index finger like I show in this article and again, I can wrap my mind around what 3 mils is.



watermark.php




I don't get how you guys can equate microns?


I know across the pond, where they already use the metric system, (it never took over here), why they can use the micron measuring standard, but over here?


:dunno:
 
Mike Phillips said:
Just to ask....


I can wrap my mind around mils.

I can hold a post-it note between my thumb and index finger like I show in this article and again, I can wrap my mind around what 3 mils is.



watermark.php




I don't get how you guys can equate microns?


I know across the pond, where they already use the metric system, (it never took over here), why they can use the micron measuring standard, but over here?


:dunno:
Click to expand...

To me it's the complete opposite. I can't understand how people are able to use a system that is so imprecise as mills ;) Once you know the baselines, microns are so much more precise (25 times more in fact).

Also I am in Canada, so I grew up with the metric system, even though I use the imperial systems for some things like lenght and weight.
 
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