What does "Burning" the paint really mean?

The term "burning" has gotten me thinking a lot recently. This is going to be a kind of rant that just basically is going to say what I have gathered from experience and reading. I may not be right, and if you believe so, just say what you think is right, basically constructive criticism. I really want to understand this better.

First thing, the term "burning" is poorly chosen IMO. Using the word gives the perception that you are heating up the paint and by producing too much heat, you are damaging it, and from what I understand, this is not the case. "Burning", from what I understand, just means that you have removed the clear coat and ran into the color coat from excessive polishing, and has absolutely nothing to do with heat. I'm sure most of you are familiar with Scottwax over on Autopia, I believe he has an account here too, but he does most, if not all of his work in direct Texas sunlight, which is hot, and then the polishing makes it even hotter, but I do not believe he has ever burned a clearcoat, and that is a lot of heat. Now, I am not saying CC's are heat-resistant or anything, just that the threshold is probably higher than most of us believe(shade only, 1,500 or less on the rotary, keep it moving to avoid heat.)

By using this term "burning", I see newbies ALL the time scared out of their mind of producing too much heat, I was one of them. They think that the heat of the rotary destroys the CC and that with a PC it is IMPOSSIBLE to "burn" through since there is no heat, which seems to be a massive misperception to me, then I see other guys telling them the same thing that it is impossible to go through the CC with the PCXP.

Just wanted to hear your opinions, just want a civil discussion about this. BTW, this pertains to metal panels, not plastic which are actually heat sensitive(from my understanding).

 

I think alot of people confuse the term burning with strikethrough, consistently using the word burn in place of strikehrough Burning, not as in charred but similar to "overcooked" per se of the paint - as in localized permanent molecular change in paint cause by too much heat for too long -Strikethrough(again, being a localized spot usually) where too much clear coat is removed and you go through that layer into the color coat. This typically happens from repeated aggressive compound or wetsanding. This is a case of just "too much"

I think "burning" as elementary as it is is a very accurate word to descibe what actually happens. Burning is a no-return type situation where too much heat causes permanent change.

Alot of people seem to think that localized burning cannot happen. I never thought it was appropriate to test the PC/UDM/XP by leaving it in one spot but things with 4inch pads can heat up in a hurry. You can even notice a significant change using 5.5 inch pads with the more power ROBS.

Another factor with both of these is the type of paint system you are talking about(CC/Colorcoat, urethane, lacquer based etc..) along with the application method and tools/products involved. Some finishes(and their superficial layers/ adherents and body panel materials are much more accepting of even a small amount of heat compared to others(metals like aluminum and steel vs various plastics)

Both burning and strikethrough situations can happen on thinner less robust paints(think of heat acceptance and dissipation), variations coming with the type of surface the paint is on. Localized spot burning can come on thick and thin and strikethrough can happen obviously on thinner but can also happen on thicker paints that happen to be softer(where more is removed per pass compared to harder paint types).

Obviously a rotary is like a WIIIIDE bit drill(basically). And therefore is more aggresive compared to an ROB with the same pad and product on the same paint.

I remember a guy on autopia striking through with some OTC product on his Porsche. Obviously not super aggressive by hand but the product and the situation of thin paint lead to his result.

 

Burning the paint is possible, it discolors the clear coat, its hard to describe, but it wont polish or sand out, what your talking about it strike through (polishing through the clear and onto the color coat), strike through is very easy with a rotary and a sharp edge where there isnt alot of paint. I think alot of the issues that you hear about from rotary polishing aren't newbies who are using the rotary for the first time, but more more advanced users who get lazy and don't really respect the power. Another issue is that all the stories are from before the different foam pads were introduced, people used wool pads to finish down etc and paint was single stage and a lacquer versus enamel.

to sum it up, i think nowadays rotary polishing is easier than before just don't get to overly proud and forget the basic rule about machine polishing (start with the least agressive method first)

 

I think you have a valid point in that "burning " may not be the best word to describe what may happen from over polishing. I do believe however that regardless of the word chosen, the message is that if you polish in one area for too long with a rotary you stand the chance of damaging or removing some clearcoat. As for Scottwax, he has only recently switched over to using a rotary. Almost all his work in the past was done with random orbital machines. Regardless, the temp outside or the temp of the paint is really insignificant to the whole scenario. Whether its 40 degrees out or 90 degrees out, if you hold a rotary in one spot for too long, you will damage the paint. Your choice of polishing pads ( hard, soft, foam or wool ) will also play a big role in how hot the paint gets as will the type of paint you are polishing. If you are using a softer pad, green for example, on softer paints you will generate a lot more heat than a hard pad spinning at the same rpm as the softer pad will produce more drag and thus more heat. I run my rotary upwards of 2500rpm at times with a compounding pad with no issues. Common sense and experience will play a role as well. The heat from the rotary in itself will not damage the paint but if you heat the paint in a given area by not moving the polisher or going over a small area consistently, the paint will become soft and the friction of the pad on the paint will be enough to remove the clearcoat. In theory, you shouldn't be able to remove clearcoat with a PC as the random orbital movement without the aid of being force driven in a circular fashion should limit the heat produced and it does so from my experience. Once again though there are always factors that can affect the outcome. I have a 92 GTI in my shop that has been polished to within an inch of its life. We are finding areas that are so thin, even using a pc with an aggressive pad could compromise the cc. Every car is different. In most scenarios though, it would be virtually impossible to remove too much cc using a PC. Hope this helps.

 

Heat is the main culprit in removing clear coat...thus the keyword "burn" being synonymous with heat.

 

Thanks for your opinions and answers. It just seems like actually burning the clearcoat is a very rare occurrence but I see the term everywhere, it just seems mis-used so much that it leads people to believe that if you don't move the rotary fast enough, the heat will destroy the clear coat, when in fact, to build up that amount of heat you would need to keep the pad in a spot for a very long amount of time, not the 2-3 seconds everyone thinks it is.


I think I need to understand how exactly the PC does not strike-through the clear coat though, for instance, the way I see it, you have a scratch that is 4.5 microns deep, so you need to remove 4.5 microns of CC to remove any trace of that scratch. I just don't see how if you know what you are doing, that removing those 4.5 microns is any safer with a PC than a rotary because you are removing the same amount of paint. It just seems to me that you accomplish the job slower with the PC, yet not any safer if you know what you are doing with the rotary, i.e. not getting too aggressive that you overcompensate for the depth of the scratch.

And thanks Ken, I guess that is where the term originates from, holding the rotary on a single spot for a very extended period of time. It just seems like that time period is much more than any rational detailer would consider or even feel comfortable with.

 

Even causing strike though requires generating a crazy amount of heat through friction which the PC is not able to produce as its not force driven. The pcs head oscillates, it does not spin so its never in the same spot. Even when removing a scratch. you keep the polishermoving, you don't hold it in one spot as you are aware. The reason using the pc is safer, is because of the rate at which the rotary is capable of removing the cc when used improperly. The pc is a slow, gradual process so its easy to track your progress. You take a wool pad and some 105 to your paint and you'd be amazed and how fast you can knock down scratches and potentially go through the clear. As for your last sentance, you'd think so but it still happens.

 

Friction is the main culprit in any kind of defect removal - heat may aid to a point - but the removal of material is what leads to defect releveling.


I still have a hard time with people saying how a PC doesnt remove clear and can't burn. For those of you who have used Spirograph. If you took the large gear(whatever they are called)(and thought of them as your pad) and ran them in the game(the boundaries being the throw of the DA), you will notice that there is ALWAYS gear(pad) in the center even though technically your pencil or pen(in a hole off center of the gear) is oscillating. Get some 4inch pads with a PC, a test panel and try the hold in one spot check for a few seconds, see how hot that ~4 inch area gets. You can remove a ton of material as well as localized burn and strikethrough with a PC and 4inch pads..

 

I do agree with you that friction is the root of all evil. Funny, I was going to use Spirograph as an analogy but figured you guys are too young to know what the hell I was talking about! LOL I agree that you would have to be somewhat developmentally challenged to say that a pc doesn't remove clear - how else would it be able to achieve any kind of correction. As for strike through however,( and I do appreciate the point you made), you would have to be an ass to hold a pc in the same spot long enough for this to occur. At some point, common sense has to take over. Hmmmmmm...... I may be able to secure a body part to test this.

 

Yea the only reason I mentioned holding the PC was I know there are a few videos of people using the underpowered PC and 6.5 inch pads and doing videos with the holding test and being fine(Junkman of Adams is 1 for sure).

I just made it a point because I know there will be that poor soul out there who sees one of them, reads about 4in pads for certain areas, incorrectly connects the 2 and assumes he can bear down on a 4inch pad and be A-OK.

I don't want to smoke a pad of mine but I think a friend has a black hood. Ill grab it and get it ready with videos to come.

 

It blows me away that people use 6.5"pads with pcs. Do you have links to any of these vids? I'd like to see one.

 

YouTube - How Safe is the PC 7424XP - Part 1 right around 7 min.

He would be sobbing if he tried that with smaller pads... I would even be weary of that (habit) pad with #85 and the PC(obviously its not gonna do anything). I remember when I first saw this saying to myself "thats gonna get someone in trouble on thin paint" But why even poke a bear in the zoo?


On a side note Scottwax in Texas still uses 6.5 meguiars pads on his Meguiars ROB.. I think that is a testament to the advancement of the machines into more power and a testament to the great pads. He has a video out too I think - I remember him moving the PC along the panel at a decent clip too

 

Thanks for the input guys. For some reason I thought Scottwax used the rotary more often, I remember him having a thread a while back about his PC giving out and he only had 2 rotaries to work with till the next PC came.

Check this vid out, for those of you who haven't seen it. It might be Dave KG? Not sure though. Looks like a 6.5 pad(dunno aggressiveness) paired with FCP and it still took that much effort. Notice in the title how it says "burn through"

YouTube - Rotary polish burn through on someones car

 

Yep, thats our buddy Dave. But its important to note, he's working on a flat panel. On an edge with that setup i would have given it 5 or six seconds, tops.

 

I think the term 'burning the paint' is more of a descriptive term than an accurate one, which has the advantage of getting the required message across.

Heat from Kinetic (or dynamic) Friction

[ : when contacting surfaces move relative to each other, the friction between the two surfaces converts kinetic energy into thermal energy, or heat]

Kinetic friction induced heat is an often misunderstood concept of polishing / compounding; abrasives require friction to breakdown, not heat; heat is just a resultant of friction between two surfaces. Kinetic friction is required to ‘level’ paint, which is simply the removal of paint to the lowest point of the paint defect. A finishing pad will not provide as much friction as a cutting foam pad, although they will both produce friction induced heat, whereas a wool pad, due to their composition, creates less friction induced heat but more kinetic friction (due to its fibrous structure) than most foam pads.

Applied Pressure

The pad needs to have an even distribution of pressure applied to it; depending on the types of surface abrasions you're dealing with, increase pressure as necessary. Just remember that more pressure equals more aggressive, so be careful around ridges and raised surfaces Maintain the same pressure and work the product in, it may take three or four passes to complete before the residue can be removed. Once you see the desired results move on to the next area, or repeat the process as necessary.

The required pressure applied to obtain optimum results to adequately compress the pad (50%) and obtain uniform abrasion is usually in the range of 10 – 15 lbs. (a random orbital buffer will stall at approximately 20 pounds of applied force) To compress a 6-inch pad 50% requires you increase the total force by the ratio of its surface areas Ratio = [π (radius2)] / [π (radius2)] = 2.25 as much force, almost 34 psi).

With the smaller pad you're applying the same force, at a constant speed but over a smaller, more concentrated area, which will induce an increase in friction and greater abrasion abilities to the polish / pad combination, both these abilities require a certain amount of caution as it’s possible to ‘strike through’ (friction burn) the paint.

 

I use 6.5 inch pads on my pc...it just takes forever to do correction

 

Switch to 5.25 - 5.75" They are easier to use, you can see around them easier when working around things and are better suited to the PC in my opinion.

 

I've since stepped up to a rotary...that was back in the day before I knew better an unscrupulous vendor sold me the kit

 

C'mon now. Don't be like that. LOL You're right though. A lot of old school guys swear by PCs with 6.5" pads but all the younger guys buying PCs are electing to go with 5.25 - 5.75" ones. Sign of the times.

 

I can agree with this. Ive proven to a few people that a PC can strike through the clear. Using M105 or Megs Power Gloss with PFW or even an orange pad, Ive polished through clear a few times on test panels to show some people it was possible. But it requires extra pressure and little movement. You have to use the PC improperly to 'burn through'.

You can also burn paint with a PC. Ive done it once accidently on a plastic panel on my own bike along time ago. The paint yellowed slightly, and from an angle, you could see how the gloss level changed drastically.