Report and pics showing how much clearcoat is removed during machine polishing

[craigdt]

My wife is about to sell her worn out 2006 Chevrolet Aveo, so what better time to answer one of life's greatest mysteries:
How much clearcoat is removed during *aggressive* swirl removal?

To try to answer this question, I used the following approach, which was somewhat popular ~4 years ago with the average hobbyist detailer:
G110V1 speed 6, moderate pressure
4" Orange LC pad
Meguiars M105

To give us a good idea of how much clearcoat we are starting with, I took paint reading around the door sill area, as it is generally not clear coated:


Average of 94 microns.

Here is the hood of the subject, to show you how bad of shape it is in:



Now testing the hood, we see the average total paint thickness reading over 5 spots in roughly a 1sq ft area is 133 microns:


So we can deduce that we have about 39 microns of clear coat to work with.

After about 8 passes, this is the result:


Now, just how much clear coat is left?




An average of 126 microns, meaning that we removed about 7 microns, or about 18% of the total clear coat layer.

Now 7 microns doesnt sound all that much, but I would think you would only want to remove at most, maybe 20-25 microns, or just over half of the available clear coat before you start to run into trouble, such as clear coat failure. Now, I am not a professional, so maybe they can chime and correct me if I am off base with this supposition.

A couple other things:
1-I was probably a bit more aggressive than I normally would be with this test. I'd probably make a few less passes, and probably use less pressure on a nicer vehicle that I cared about.

2- This really enforces the importance of proper wash/general care techniques, since you may only have 2 or 3 chances at heavy compounding before you might start to think twice and choose a lighter polish.

3- Different vehicles will have different thicknesses of clearcoat. So what may get you in trouble on one vehicle would be perfectly fine on another. A paint thickness gauge could very well save you from a bad day.

4- Detailing is fun

[LSNAutoDetailing]

Good write up! It really depends on the vehicle, hardness of the clear, and the aggressiveness of what products are used.

However,You prove two very important points:

1. Always do a test spot
2. Test with the least aggressive methods & product to see if it will accomplish the goal for a defect free shine.

[TTQ B4U]

Good write up! It really depends on the vehicle, hardness of the clear, and the aggressiveness of what products are used.

However,You prove two very important points:

1. Always do a test spot
2. Test with the least aggressive methods & product to see if it will accomplish the goal for a defect free shine.

^^ Agree that this is a great write up and reminder to all. I am glad that in most every case, I'm able to achieve success with just a simple fine polish. I also do my best to maybe use it once in the spring and then to perform only a light touch up mid summer to get me through the season of fun in the sun.

[Setec Astronomy]

Now 7 microns doesnt sound all that much, but I would think you would only want to remove at most, maybe 20-25 microns, or just over half of the available clear coat before you start to run into trouble, such as clear coat failure. Now, I am not a professional, so maybe they can chime and correct me if I am off base with this supposition.

If I recall correctly, based on a nominal 2 mil clearcoat thickness (~50 microns), it is recommended that you remove no more than 0.5 mil (~12.5 microns) to preserve the UV integrity of the clearcoat.

The difficulty in determining that is that you don't know how much you, a previous detailer, a prior owner, may have removed before you took that first reading. Even if you are the original owner, the dealer may have done who knows what to the vehicle while they had it.

I remember looking on the back lot of a local dealer perusing their inventory, and the last row of the lot, the cars were covered, and I mean covered, with bird poop due to the overhanging trees that abutted the lot. Makes you wonder what they did in the detail bay before they delivered those cars.

I bought a car that had been sitting on another dealer lot for a long time, and asked them not to wash it before delivery. When I got the car home it felt like sandpaper, except for one foot-square spot on the trunk that was smooth as glass...I always wondered what was on that spot and how much paint they took off removing whatever it was.

Great test though and thanks for documenting it.

[mbkite]

Good to see people posting on paint thickness gauges.
I took the plung my self and got a highline from AG
Still learning how to use it but . Polished a f 250 with it and it does inspire confidence.. So keep the tread alive and add your thoughts on how to use..and any good tips.

[glfnaz]

To me it is confusing. The OP feels they removed @ 7 microns in this polishing.
Setec says one should only remove 12.5 microns over the life of the car before you are getting to UV coating removal (sounds like that is a very bad thing where you will face potential clearcoat issues.

That then tells me 2 polishing sessions like the OP just described is problematic. Is this correct? Or did I flunk math?

[Eldorado2k]

Speed 6 w/4" Orange cutting pad? Man that's pretty aggressive..

Just the other day, I recall hearing someone say that using a 3-4" pad is like wielding a mini rotary..

Also, did you take the after measurements immediately after taking the polisher off the paint? I could be wrong, but I think I heard that in order to get the true measurement it's best to allow the panel to completely cool off. That may or may not be critical, just thinking out loud.

[FUNX650]

To me it is confusing. The OP feels they removed @ 7 microns in this polishing.
Setec says one should only remove 12.5 microns over the life of the car before you are getting to UV coating removal (sounds like that is a very bad thing where you will face potential clearcoat issues.

That then tells me 2 polishing (compounding) sessions like the OP just described is problematic. Is this correct?
Or did I flunk math?

^^^When it comes to compounding:
Yes...that's pretty much the case!

And, IMO:
The OP pretty much hit that nail on the head
by posting these sentiments:

A couple other things:

1-I was probably a bit more aggressive than I normally would be with this test. I'd probably make a few less passes, and probably use less pressure on a nicer vehicle that I cared about.

2-This really enforces the importance of proper wash/general care techniques,

since you may only have
2 or 3 chances at heavy compounding

before you might start to think twice and choose a lighter polish.

Bob

[craigdt]

To me it is confusing. The OP feels they removed @ 7 microns in this polishing.
Setec says one should only remove 12.5 microns over the life of the car before you are getting to UV coating removal (sounds like that is a very bad thing where you will face potential clearcoat issues.

That then tells me 2 polishing sessions like the OP just described is problematic. Is this correct? Or did I flunk math?

Like Bob said, this is correct, based on what Setec is saying.
Removing "only" 7 microns doesn't seem that bad, but could lead to trouble down the road.

Makes me think that the UK guys and their glazes might be on to something...

[craigdt]

Speed 6 w/4" Orange cutting pad? Man that's pretty aggressive..

Just the other day, I recall hearing someone say that using a 3-4" pad is like wielding a mini rotary..

Also, did you take the after measurements immediately after taking the polisher off the paint? I could be wrong, but I think I heard that in order to get the true measurement it's best to allow the panel to completely cool off. That may or may not be critical, just thinking out loud.

Yep- being aggressive was the goal here. Different folks grade aggressiveness differently, but I don't know that I'd quite go as far as comparing it to a mini rotary.

Also, I didn't not take temperature readings (great idea, btw) but the panel was not hot, by any stretch of the imagination. I farted around for a couple minutes before taking the reading. I'm sure the panel was warmer then before polishing, but not by much.

Thanks for all the comments! I get caught up in product hype as much as the next guy, but sometimes we need to remind ourselves of the basic facts behind our hobby, which is why I love the detailing "science" topics.