Paint Removal by Polishing - Rotary Example

[imported_Dave KG]

One of the most important factors of polishing, be that by hand or by mahcine, is the amount of paint that you are removing from the car with any given polishing method. In this thread, I am going to outline an example of a car which is being polished and the amount of paint removed by each set of polishes - there's more here than simply how much paint removed and what results it gives, there's also something well worth noting which we will get to at the end



The car used in this example: A white (faded) Vauxhall Vectra SRi V6:

The paint was well faded...

The full detail on this car will be the subject of a writeup in a few days time - I have a visitor from Romania, Alex, who is learning the ropes of detailing with me and this is one of his projects But for now, this car will be sued as an experiment base for this example



First of all, we measure the paint thickness on a selected spot on the car, round a stone chip that wont polish out we took 10 or so readings of the paint thickness over the same spot and calculated the average thickness before starting to polish.



The starting thickness: Start Thickness = 119.0um



First of all, the car was polished using Menzerna PO85RD Final Finish on a Meguiars Finishing pad - very light combination, not expected to achieve much correction or remove much paint. The results of polishing with this combo, by rotary, using the Zenith Point Technique:

Under the Sun Gun, the colour and some of the gloss restored but still a lot of scratches there...

Using the strip light we can see the deeper RDS better, and also we see a pitting in the paintwork - this is a road rash, lots of little stone chips which are very deep into the paintwork. We will look at removing these and the thicknesses removed required to do so...

The thickness after one hit of 85RD: After 85RD = 117.3um

A removal of: Paint removed = 1.7um



Now, stepping up to Menzerna PO106FA Final Finish, applied using a meguiars W8006 polishing pad using the Zenith Point Technique and we get the following results under the Sun Gun:

and under the strip light, where we still see deeper scratches and the pitting...

The paint thickness after 85RD and 106FA: After 106FA = 116.6um

A removal of: 106FA Removal = 1.1um



Stepping up again, to Menzerna PO85RD3.02 Intensive Polish on a polishing pad, applied using the Zenith Point Technique and we get the following results...

Under the strip light we see the deeper RDS are now largely removed, but the pitting remains strongly...

Definitely making a difference to the finish though!

The paint thickness after 85RD, 106FA and 85RD3.02: After 106FA = 116.2um

A removal of: 85RD3.02 Removal = 0.4um



With less than 3um of paint removed this far, it was decided it was safe to step up to more aggressive compounding to see if the pitting could be minimised further. So, up to 3M Fast Cut Plus, Meguiars W7006 cutting pad, applied by spreading at 600rpm and working at 2000rpm until residue goes clear and machine starts to drag slightly. Results after one hit of FC+:

Under the strip light, still see the pitting but its getting better...

The paint thickness after 85RD, 106FA, 85RD3.02 and FC+: After FC+ (1st) = 114.4um

A removal of: FC+ Removal = 1.8um



A second hit of FC+ gives:

The paint thickness after 85RD, 106FA, 85RD3.02 and 2xFC+: After FC+ (2nd) = 115um

A removal of: FC+ Removal = -0.6um (paint added - this is measurement error)



A third hit of FC+:

The paint thickness after 85RD, 106FA, 85RD3.02 and 3xFC+: After FC+ (3rd) = 113.2um

A removal of: FC+ Removal = 1.8um



As the pitting is minimising but still there, we keep going with FC+ - we could get more aggressive with #105 or wool here, but the FC+ on foam allowed for a flexible and controlled removal rate.



So - after 4th hit of FC+:

Pitting definitely improving here. Paint readings:



The paint thickness after 85RD, 106FA, 85RD3.02 and 4xFC+: After FC+ (4th) = 108.4um

A removal of: FC+ Removal = 4.8um

 

[imported_Dave KG]

Bigger paint removal here.



5th and final hit of FC+ gives:

Under the strip light we can see the pitting well and truly deadened if not fully removed (remember, these are pin pricks from stones and grit, so they are deep!):

What of the paint thicknesses?:



The paint thickness after 85RD, 106FA, 85RD3.02 and 5xFC+: After FC+ (5th) = 107.1um

A removal of: FC+ Removal = 1.3um



The finish was then refined using 106FA on a polishing pad, and this gives the following final finish results - still slight evidence of the pitting, but with notable paint removal now, it is best to leave these marks to allow for future correction on the car at a later date, as this pitting will return with more miles (currently 100k on this car just now).

The paint thickness after 85RD, 106FA, 85RD3.02 and 5xFC+, 106FA: After 106FA refine = 107.1um

A removal of: FC+ Removal = 0.0um



Overall, we have removed a total thickness here:



Total Paint Removed = 11.9um



which has been enough to go from this:

to this...

So, what has all this told us?



First of all - you think Vauxhall paint is soft?! Well, 5 hits of FC+ and we are only just over 10um of paint removed, so soft is certainly not something we can level at this finish - its always best never to assume the paint hardness as some cars are just different for a variety of reasons.



Next, look at the initial removal from 85RD - its more than for IP, and similar to FC+! Now this could be put down to gauge error, but this is a consistent finding I am seeing. It would appear the top layer of the paint is consistently softer (especially on older cars) which is possibly down to UV degredation, softening the upper layers of the paint. In any case, expect initial removal rates to be higher than following removal rates as this example shows.



On the subject of gauge error, you can see that there is notable gauge error here so you should only use the numbers as a guide, an estimate. Take more readings per average and you will help to reduce the "noise" in your data



I hope this proves interesting food for thought on paint removal rates when polishing, just as an example on a real car

 

[sejodiren]

Amazing...your write-ups are top notch! And I always enjoy them and the results you achieve. Hope you post a pic of the finished car!

 

[imported_gusbubba]

Great work, man. Well thought out and presented.

Thanks for taking the time to educate.

 

[craigdt]

Very nice. These sort of threads are my favorite.

 

[David Fermani]

Nice Dave - I'd like to know what the measurement and the appearance of the finish would be like in comparison if you sanded instead of making multiple passes with FC.

 

[imported_Conan777]

Nice thread I've been pondering doing a similar experiment of my own. Thanks for taking the time to post.



What do you guys think is the max amount of clear you can polish down to before you go too far? I have been told that you want to avoid going any deeper than 80um otherwise risk clear coat failure, what about single stage paints???

 

[acc1079]

Thanks for the post. Great information!!

 

[the other pc]

Another great post, Dave! :hifive:



(Not that I'd ever expect anything less.

)





pc.

 

[imported_Dave11]

Excellent stuff.....





Very informative, thanks for taking the the time to document that with those wonderful photos.........:2thumbs:

 

[bigjizzles]

great job!!! this is really helpful.



This can also change the "start with least aggressive" myth



Because multiple passes with a polish could possible remove more clearcoat than a single pass with a compound!!!



great writeup.



Hope to see more like this with other polishes!

 

[imported_Dave KG]

Nice thread I've been pondering doing a similar experiment of my own. Thanks for taking the time to post.



What do you guys think is the max amount of clear you can polish down to before you go too far? I have been told that you want to avoid going any deeper than 80um otherwise risk clear coat failure, what about single stage paints???

On this car, there is no clearcoat... another thread I am working on may help answer that question...



But the real answer is that it depends - sorry, a bit wishy washy, but every car is different... The key is to aim for the best correction with minimal paint removal. Clearcoat is a layer designed to "weather", and protect the underlying colour coats. The thinner you make it, the less protection it offers, especially to the interface layer between it and the colour coat on which is sits... UV penetration can weaken this and lead to peeling of the clearcoat prematurely. So you want to avoid making the clearcoat thin - its not a case of being able to take the paint finish to 1um of clear and all is good!



80um - well, alas, that is just a number and it may be correct for one car... but not for all. Take a Mazda RX-8, you'll be lucky to see 80um of paint on that from the factory, and it will not strike though to 40um (generally speaking, please do not read that as gospel and try to take RX-8 paint that far - I'm just using numbers as an example!!!). My Astra test car however started with 120um and strikes through at around 85um - so 80um would be too low!



The key is to look at the car as a whole - how consistent are your paint readings, any thin spots? Any thin panels? If it all starts around the 120 - 140um, taking it below 100um is not adviseable. If its been resprayed and is sitting with 300um of paint, then taking of 10um could be considered risky depending on who sprayed the car.



So many variables - but thats what makes it fun

 

[Accumulator]

What do you guys think is the max amount of clear you can polish down to before you go too far? I have been told that you want to avoid going any deeper than 80um otherwise risk clear coat failure, what about single stage paints???

The industry guys I've spoken with (e.g., Ron K.) lean towards the limit being a percentage of whatever clear was deemed "right" when it was painted. It's generally something like "the top 45% of the clear contributes almost all the UV protection" or something like that.



The generalizations about the actual/absolute amount usually run along the lines of ~0.50 mils being the max you should remove. But of course, half-a-mil is a lot different on an Audi than it is on a Mazda because of how different they are to start with.



Oh, and Dave KG isn't kidding about Mazdas being thin; some areas on my seldom-polished MPV are right at 3 mils. No, I don't park it in the sun more than I have to