Over polishing clear coat?

[lkotsios]

Am I in danger of thinning clear coat from over polishing on a 93 Vette? This is what I have done over the passed 3 years or so on my car with a PC 7424xp speed 4.5,

Megs ultimate compound 3 times with orange pad
Megs 205 6 times with a black pad
85rd 7 times with a black pad

[embolism]

only way to know is to get a paint gauge and take lots of measurements. Even then, it's a bit of a guessing game.

vette is older model (before they started getting cheap on paint) and the clear is hard so it may have stood up to the UC quite well.

[lkotsios]

only way to know is to get a paint gauge and take lots of measurements. Even then, it's a bit of a guessing game.

vette is older model (before they started getting cheap on paint) and the clear is hard so it may have stood up to the UC quite well.
Does paint gauge work on fiberglass and if so would it measure clear and paint together or can I measure clear alone?

[CEE DOG]

My paint gauge cost a couple hundred bucks and works well for ferrous or non ferrous metals. Easy to use, only problem is the ones in this range and even a lot more expensive don't tell you how much of it is clear. My buddy Richy gave me some great tips and tricks on how to get an idea of what you have in clear and how to judge what is ok to work with but the truth is you don't know for sure how much clear you have at a given point with one of these units. You have to spend a lot more for that!

For fiberglass you are looking at spending thousands for a really good unit that can read paint thicknesses on that material and tell you how much primer, color, and clear coat you have.

[lkotsios]

My paint gauge cost a couple hundred bucks and works well for ferrous or non ferrous metals.

For fiberglass you are looking at spending thousands for a really good unit that can read paint thicknesses on that material and tell you how much primer, color, and clear coat you have.
With the polishig I have done have I removed a lot of clear?

[CEE DOG]

There is a ton of unknown variables (pad type, pressure, etc) but I would say in the grand scheme you have cut a very small fraction of the percentage of clear you have. Unless of course the owner before you (if there was one) polished the hell out of it or ate up a bunch of the clear.

I have read some things that talked about my following question but I don't understand the logic in what I've read about this... Does the upper layer of the clear have more UV protection in it than the remaining layer and thus more important? Hmmm

This brings up some important subjects in my mind i have never got a satisfactory handle on...
If you notice when you see most clear coat failure the clear hasn't been polished off.. Instead it is peeling off the color coat. So, why is it peeling off? Heat and cold temperature fluctuations that cause one layer of paint to expand and contract faster than the other? The fact the clear layer gets heated more than the layer beneath from not only the sun but from anytime you polish it? Arrrgh, a bunch of other stuff I'd like to say and question here but gotta get back to work.

[Setec Astronomy]

I have read some things that talked about my following question but I don't understand the logic in what I've read about this... Does the upper layer of the clear have more UV protection in it than the remaining layer and thus more important? Hmmm

This brings up some important subjects in my mind i have never got a satisfactory handle on...
If you notice when you see most clear coat failure the clear hasn't been polished off.. Instead it is peeling off the color coat. So, why is it peeling off? Heat and cold temperature fluctuations that cause one layer of paint to expand and contract faster than the other?

Could be as simple as the clear has a specific UV absorbance value per unit of thickness, and that the thinner the layer gets, the less UV is absorbed, until a critical thickness is reached. It could be the "top surface has the mose UV protection" meme is just a mistranslation from chemist to layman-speak. Or it could be that when the clear lays out after spraying that some components float to the top, the way you "float" concrete to not have exposed aggregate.

As far as the peeling, might just be that with the reduced thickness the layer of clear has less bending strength, or the lack of UV protection affects the bond between the CC and the BC.

The thing that always torques me about these discussions is I'm sure there are guys at PPG and DuPont, BASF, etc, maybe even Dr. G who know exactly the mechanics involved in CC failure, but we can never seem to connect any of those guys to the forums to get these answers. Maybe because they can't explain these things in terms laymen will understand, so it becomes frustrating for both parties.

[CEE DOG]

Could be as simple as the clear has a specific UV absorbance value per unit of thickness, and that the thinner the layer gets, the less UV is absorbed, until a critical thickness is reached. It could be the "top surface has the mose UV protection" meme is just a mistranslation from chemist to layman-speak. Or it could be that when the clear lays out after spraying that some components float to the top, the way you "float" concrete to not have exposed aggregate.

As far as the peeling, might just be that with the reduced thickness the layer of clear has less bending strength, or the lack of UV protection affects the bond between the CC and the BC.

Well written points and theories.

Perhaps we have never asked the right questions. I reached out to our most respected chemical engineer with the hope we will be further educated on this subject.

[KneeDragr]

I was under the impression that the amount of paint a DA removes is trivial compared to what rotary or wetsanding does. The DA from my understanding does not fully remove defects as much as it smooths them out so they are mostly invisible. From that I gathered that you could probably do a couple dozen compoudings, and twice that many polishies before you started to worry.

Dont take my word for it though, Im sure there are people that know a lot more about it.

you could always get the car wet sanded and re-cleared with 2-3 coats of high quality clear. Not every bodyshop will want to do it but that should give you another couple decades worth of corrections.

[SRTSean]

I don't know if there's much truth to this, but I've heard that as long as there is a bit of orange peel texture then you still have plenty of clear (assuming we are talking about factory paint).

[lkotsios]

I don't know if there's much truth to this, but I've heard that as long as there is a bit of orange peel texture then you still have plenty of clear (assuming we are talking about factory paint).
That sounds like it makes sense, I still have orange peel showing.

[FUNX650]

Does paint gauge work on fiberglass and if so would it measure clear and paint together or can I measure clear alone?

As Corey (CeeDog) mentioned....quite pricey!!
__________________________________________________ __

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Manufacturer Item #: POSITECTOR 200 B-ADV

Your Price $2,875.00 (I'll add: This low, low price is from a 'discount' electronic house :))

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This Defelsko coating thickness gage non-destructively measures a wide variety of applications using proven ultrasound technology. Measures coating thickness over wood, concrete, plastics, composites and more. Proven non-destructive ultrasonic technique conforms to ASTM D6132 and ISO 2808 and SSPC PA9. This advanced model measures total thickness of a coating system or up to 3 individual layer thicknesses in a multi-layer system. Also features graphic readout for detailed analysis of the coating system. The B probe is for use on polymer coatings on wood, plastic, composites, etc.

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__________________________________________________ __



[IMO..It would take a lot of detailing jobs to pay for this PTG. Unless those detailing jobs were some of Paul Dalton's.] :D


In more recent years, the OEM's stated amount of total clear-coat removal they will allow is in the 0.3mil(about 7microns)-0.5mil(about 12microns) range before it voids the paint warranty.

Where the UV protection lies within the clear coat is a justifiable concern. Everyone that details may not have a PTG; but, if a clear-coat paint failure does arise; and, a consumer wishes to persue this matter with an OEM's "complaint department"; then, I'd almost guarantee that an OEM's "complaint-department-inspector" will.

This may not apply to your particular vehicle, just something to think about for future reference, if you so wish.:)

Bob

[lkotsios]

As Corey (CeeDog) mentioned....quite pricey!!
__________________________________________________ __

Defelsko Coating Thickness Gage for Non Metals, PosiTector® 200 Series w/ B Probe - Advanced Model

Manufacturer: Defelsko Corporation
Manufacturer Item #: POSITECTOR 200 B-ADV

Your Price $2,875.00 (I'll add: This low, low price is from a 'discount' electronic house :))

Features & Applications:

This Defelsko coating thickness gage non-destructively measures a wide variety of applications using proven ultrasound technology. Measures coating thickness over wood, concrete, plastics, composites and more. Proven non-destructive ultrasonic technique conforms to ASTM D6132 and ISO 2808 and SSPC PA9. This advanced model measures total thickness of a coating system or up to 3 individual layer thicknesses in a multi-layer system. Also features graphic readout for detailed analysis of the coating system. The B probe is for use on polymer coatings on wood, plastic, composites, etc.

Type: Advanced Electronic
Base Material: Non Metals Such As Concrete, Wood And Composite
Measuring Range: 0.5 to 40
Accuracy: +/-0.1 Mils + 3%
Data Storage: Yes
Interface: USB, Serial And Infrared
Recording Capacity: 10,000
Cord Length: 3 Ft
Calibration Certificate: NIST
Battery Type: AAA
Includes: Plastic Shims, Protective Rubber Holster, 3 Batteries, Nylon Carrying Case, Couplant and Instructions
Product Description: Price: Your Cart:
Ultrasonic Couplant - 4 oz. - Pkg of 12 $118.95 Add
__________________________________________________ __



[IMO..It would take a lot of detailing jobs to pay for this PTG. Unless those detailing jobs were some of Paul Dalton's.] :D


In more recent years, the OEM's stated amount of total clear-coat removal they will allow is in the 0.3mil(about 7microns)-0.5mil(about 12microns) range before it voids the paint warranty.

Where the UV protection lies within the clear coat is a justifiable concern. Everyone that details may not have a PTG; but, if a clear-coat paint failure does arise; and, a consumer wishes to persue this matter with an OEM's "complaint department"; then, I'd almost guarantee that an OEM's "complaint-department-inspector" will.

This may not apply to your particular vehicle, just something to think about for future reference, if you so wish.:)

Bob
So what do you think with the polishing I have done on 93 vette, have I gone through much clear?

[maluminas]

I'm pretty sure the top layer of clear coat does not have better UV absorbance. And as someone else pointed out, i think it's a "mistranslation". Let me attempt to explain...

In spectrophotometry, absorbance is the property of a material to absorb a particular wavelength of light at a specific rate dependent of the thickness of said material traversed by said light.

Imagine a thin film of clearcoat, 1 micrometer thick. Imagine that this thin film absorbs 50% of the UV light that hits it (i'm makin up numbers here). This means that 50% of the UV light makes it to the other side. Now add another micrometer of clearcoat after the first one. Will it block all the remaining UV since it will block another 50%? No! It will block 50% of the remaining 50%. In other words, it blocks half of a half, meaning that a quarter (25%) or the initial UV intensity makes it through the 2 micrometers of clear coat.

Now keep adding micrometers of clearcoat. At 3um, 12.5% makes it through, at 4um its 6.25%, 5um is 3.13%, 6um is 1.56% etc.

If for every layer you divide the remaining UV by half, it means that, in theory, you will never block all of it, because even after an inch of clear coat, you might have 0.000000000001% of UV going through.

Now how does that tie in with the theory the the first layers are more effective? Its because the first layers have more remaining light to absorb that the layer following it, giving the illusion that, overall, the first layers are more effective.

Now if we go in reverse... Imagine you have 3um of cleacoat, so you have 12.5% of UV going through. We still agree that the first layer stops 50% of it, then the second layer stops 25% of the initial 100%, then the third layer stops 12.5% of the initial 100%, so you have 12.5% left.

If you remove the first layer by polishing it off, you will not be letting 50% of the UV through because the first layer blocked 50%, you simply now have two layers. This means that the first layer (which was second before) now block the first 50%, and the second layer now blocks 25%, so now, since you have 2 layers, you have 25% of the UV going through.

To summarize, you removed a third of the clear, and the UV going through doubled. If you remove another layer, the UV will be four times more intense after it goes through the clear (50% will go through, which is 4x12.5).

In conclusion, the top layers do not have a higher absorbance, it only means that the amount of UV that makes it through is inversely exponetial to the amount of clear you have.

Basically, the less you remove, the better it is... Did that make any sense? lol

[Bunky]

If you really want to get your paint measured, go to a body shop and see if they will measure it for say $25. It is a lot cheaper than the tool for fiberglass. If they have no paint gauge, this may tell you something about the shop.