Paint Surface Temperature Discussion

I

imported_zenhog

New member
I'm sending up a pic of the temp I took of my car sitting outside today under a slightly-overcast sky.



150+ degrees!



Yesterday when I bought the Radio Shack gauge there was direct sunlight, no clouds, and spots were 170+ degrees!



I don't know where this idea came from that if, while polishing, you'll burn your paint if you get the surface temp to 150 or higher, but unless we're all running around with burned paint jobs, I think that temp statistic may need to be re-visited.



Or maybe someone can explain to me why 150 under the sun is different than 150 under a foam pad?
 

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Theveed is in the right direction. Friction of buffing literally moves molecules on the surface of the finish. That is what leaves buffer swirls.



The static temp of your paint in the sun is an example of wht sealants (with a >300 degree melting point) are superior to waxes (with a 165 degree melting point).



Did you take the interior temp? It is pure hell in there!



Jim
 
No, I didn't take the interior temp, but that brings up a good thought. No wonder why dogs don't last very long in a car in the heat!



But.. that's not a problem with me.. (I have a convertible) lol



It's going to hit 100 here today, I'll try to get outside and catch a temp reading during the heat of the day. I bet I get something around 170 or more!



C
 
jimamary said:
Theveed is in the right direction. Friction of buffing literally moves molecules on the surface of the finish. That is what leaves buffer swirls.
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I don't buy it. . .

1) High speed rotary buffer can induce temps in excess of 150F easily. I would not be surprised in temps of 400F+ were reached in local hots spots.



ie. I do alot of aluminum polishing and buffing with high speed buffers and polishing compounds. This often yields aluminum at temps that are in excess of the melting point of many plastic, in other words, I can melt plastic on a aluminum surface that I have buffed.



2) You are not going to move the "molecules" or clearcoat if its still in solid form. You must heat it to the point where it begins to flow which will be at or near melting point of the clearcoat.
 
BryanPendleton said:


2) You are not going to move the "molecules" or clearcoat if its still in solid form. You must heat it to the point where it begins to flow which will be at or near melting point of the clearcoat.
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Actually, you don't need high temperature to move molecules.



Wet-sanding for example moves molecules without heat.



(assuming your wet sanding water is out of the cold side of the sink or out of the garden hose).



This would have to do with the abrading characteristics of whatever product your using.



Another example would be how old timers would hand rub lacquer finishes using either a traditional compound or a diminishing abrasive like MGH-4 Hand Cleaner, (pre-1940's).



Yet another example would be the Porter Cable Dual Action Polisher. One of the reasons its safe is because it Jiggles instead of rotates via direct drive. While yes, it can generate heat, it’s abrading power comes from the application material, your choice of chemical, pressure, time, heat and physical action. It’s a combination of all of these that are doing the abrading, but they are not necessarily dependent upon heat in order to remove/flatten/polish/smooth-out paint.



FWIW
 
the kenetic energy enduced by a polisher is used towards abrading the surface



if it wasn't then it would heat up (takes a lot of kinetic energy to make heat)



going the other way around is different (and harder to theorize), it takes a lot of heat energy with out kinetic to induce abrasion the other direction.



the temperature of the pigmented paint is going to be different form that of the clearcoat paint, use a thermocouple instead and try to get a surface reading.



just theories, i guess ???
 
Mike Phillips said:
Actually, you don't need high temperature to move molecules.



Wet-sanding for example moves molecules without heat.



(assuming your wet sanding water is out of the cold side of the sink or out of the garden hose).



This would have to do with the abrading characteristics of whatever product your using.



Another example would be how old timers would hand rub lacquer finishes using either a traditional compound or a diminishing abrasive like MGH-4 Hand Cleaner, (pre-1940's).



Yet another example would be the Porter Cable Dual Action Polisher. One of the reasons its safe is because it Jiggles instead of rotates via direct drive. While yes, it can generate heat, it’s abrading power comes from the application material, your choice of chemical, pressure, time, heat and physical action. It’s a combination of all of these that are doing the abrading, but they are not necessarily dependent upon heat in order to remove/flatten/polish/smooth-out paint.



FWIW
Click to expand...



Yes, I am aware that you can move clearcoat and paint molecules by abrasding and sanding, etc. But Zenhog's reference was towards "burned paint jobs", which can occur using a high speed rotary buffer/polisher. His confusion, was that he was told paint "burns" at 150F, but he is measuring temps in excess of 150F just sitting outside. My argument is that paint temperature reach temps well in excess of probably 300F, when burning the paint with the use of a rotary buffer. The "burning" that occurs with rotary buffer use, from my understanding, is:



a large portion of the kinetic energy from the buffer in being converted to heat energy at the interface between the paint and buffer. When the heat in that localized area cannot be transfered away fast enough the paint becomes heat saturated, and temps begin to elevate to the point when the clear or paint actually begins to flow.



That is my understanding of "burning" paint with a rotary, and it is my understanding that this occurs because of the excessive temperatures which the paint reaches. Sure the chemical, pressure, time and buffer action all come into play. The combination of those are what actually determines how much heat is generated through the conversion of kinetic energy to heat energy



I am open for discussion.
 
Your description of when paint begins to burn sounds right on to me.



Burnt paint.



Been there... done that.... don't want to do it again.





Mike
 
This was 2 PM today.



I think this is great discussion. I don't see a post yet that explains where or how the traditional thinking came from.
 

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zenhog said:
if while polishing, you'll burn your paint if you get the surface temp to 150 or higher
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I don't know where this came from, if it came from "a source", then it's probably just a general, good rule of thumb.



Here is what I do know.



Burning paint, which can mean,



a. Discoloring light colors due to concentrated pressure/temperature

b. Removing enough paint to actually expose either the base coat under the clear coat, or the primer under a single-stage



is going to be different on every car you ever buff out.



For these reasons.



Paint hardness

Paint thickness

Paint material



Things that will influence burning are,



Pad type - wool or aggressiveness of foam

Chemical - type of abrasive - diminishing or non-diminishing

Carrying-agent - percentage of water, solvent, or oils

Time spent buffing

Pressure exerted

Ambient temperature



Something to think about...



If your heating the surface temperature to 150 degrees with a wool pad and an aggressive, pasty compound, versus heating the surface temperature to 150 degrees with say, a Meguiar's W-8000 with a very slippery machine glaze like M-03, I know the wool pad with the compound will burn the paint easily and quickly while the foam pad and the M-03 will tend to be a lot more slippery on the surface allowing you to get away with a higher surface temperature without burning.



Whether or not your burn through paint is going to be a mix of all the right conditions, (actually wrong conditions), in order to result in burning through paint.



Too much pressure and too much time with any combination of product and pad will result in a burn through.



The best thing you can do is buff with common sense, here’s how,



After buffing for a few passes, feel the surface your buffing with the palm of your hand, if it's too hot to touch, or even real uncomfortable... stop buffing until the surface cools down.



One other thing,



Whenever I buff out a car for a customer, I take into consideration that I have no idea, "who has buffed the paint before me", let alone what they used, and specifically how much paint they have already removed.



It's possible that the paint looks good as you and the owner stand their and look at the finish, then, one pass with a foam pad and a light cleaner/polish and you’ve burned through the paint...



Any company's product would have been aggressive enough to burn through because there was only microns of film-build left on top of the base coat, or primer.



You just happen to be the lucky person to make the last pass, and I mean the last pass



When you see you have buffed through your paint, or worse, a customers paint, you will be amazed at how fast you can take your finger off the trigger and remove the buffer from the surface.



Best advise I can offer to those who want to use a rotary buffer, but don’t want to burn through paint is,



Make a mistake



Just don’t' do it on anything that’s important.



This means find a junker car and purposefully burn through the finish, or go to the local wrecking yard and purchase the hood or deck lid off a car and practice buffing on it, including purposefully burning through it.



By learning what not to do, you will know better what to do.



A little story,



In my home town, just down the road was a wrecking yard that had been there since the beginning of time. Since I was 16 years old, I had been going there and scavenging parts, I was actually there in the mid-70's when they still had cars from the 40's there. This was particularly helpful for me considering the second car I owned was a 1948 Plymouth coupe.



Point being, I knew the owners and employees well enough that I could go down their with my Makita rotary buffer and the 100' cord I wired into it, (and a couple of extra extension cords), and buff on all kinds of paints till my heart was content.



Just for fun, I burnt through the paint on number of cars resting in peace.



So the 150 degrees is probably just a good rule of thumb.



A better practice/rule of thumb is to get experience by placing your hand on the surface and getting a feel, (literally), for how long you can buff a panel, (for the particular car your buffing on), with your choice of pad and chemical, and the amount of pressure your exerting for the goal your trying to achieve, (i.e. you will be exerting more pressure trying to remove sanding marks, versus just removing some light scuffs and mars).
 

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Thanks Mike, that makes a lot of sense. The body shop that did a repair for me recently invited me to come get whatever they have laying around to practice on - I think I'll take them up on the offer.



c
 
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