I do not understand why buffing and sanding gets out a scratch.

S

ShowCar

New member
Jun 1, 2013
25
0
Dumb question. If you scratch the paint on a car, light to medium scratch, why does buffing it with a compound get rid of it? It's still cut into the paint. I know it works but I don't understand it.

Another one I saw was someone using fine grade sandpaper, wet. Now how come that doesn't ruin the car's paint job? It didn't. Sanded and then buffed. Why didn't he have to repaint the thing?

I know these are crazy, but I want to understand. Thanks for help.
 
ShowCar said:
Dumb question. If you scratch the paint on a car, light to medium scratch, why does buffing it with a compound get rid of it? It's still cut into the paint. I know it works but I don't understand it.

Another one I saw was someone using fine grade sandpaper, wet. Now how come that doesn't ruin the car's paint job? It didn't. Sanded and then buffed. Why didn't he have to repaint the thing?

I know these are crazy, but I want to understand. Thanks for help.
Click to expand...

When you sand or buff out a scratch, you are removing clear coat around the scratch, thus leveling around the scratch making it less visible. A deep scratch would require filling with touch up paint.
Wet sanding does not remove the color coat, it removes the clear coat. Polishing will bring back the gloss in the clear coat. If you went down to the color coat you would have to re-paint (color coat + clear coat).
 
There's a layer of clear coat on top of the base coat which is the actual colored layer of paint. The scratches rarely go all the way through the entire layer of clear coat. So what you are doing is lowering the level of clear coat to a level below the depth the scratches are, so the clear in that area is flat and level across it.
 
You should watch Junkman's how to for novice video part1. He gives a good explanation as to why buffing takes out scratches.
 
OEM (factory) clear coats are about 50 microns thick, but a typical scratch may only be one or two microns deep. Compounding removes one or two microns (more or less depending on the aggressiveness of the pad, compound, and technique). Note: these aren't necessarily exact numbers - the point is that minor scratches and basic compounding impact only a fraction of the clear coat layer. Obviously deep scratches are a different story...
 
Thanks guys. That helps a lot. It was just a mystery to me. I'll find the Junkman videos too.
 
When you guys talk about scratching paint with microfiber, does that mean the clear coat as well?

edit: for that matter, how in the heck does cloth scratch something?
 
ShowCar said:
When you guys talk about scratching paint with microfiber, does that mean the clear coat as well?

edit: for that matter, how in the heck does cloth scratch something?
Click to expand...

Sometimes the finish of a vehicle is referred to as simply 'paint', not everybody wants to say "I scratched the clear coat with my microfiber" even though it is more accurate phrasing, the fact remains that it's still largely referred to as paint for simplicity's sake.

Clear coat is very, VERY thin. That of a post it note, give or take. Some clear coats (typically Japanese, Subaru, or BMW jet black for example) are much softer than other clear coat systems (like that of Audi, BMW, GMC, etc).

When you drag your microfiber across the finish of the vehicle, despite how glossy and smooth the finish may be, your fibers are dragging against the paint, creating friction, and on a soft enough paint system, micro-marring. Couple that with the possibility of contaminates getting into your towel while you're buffing and well, yeah...
 
Oh. I see, but isn't this the coat the gets the bugs, droppings, protects from UV and all that? Seems like it would be tougher than that. Strange how things really work. I never thought detailing was, so, well, detailed. :)
 
ShowCar said:
Oh. I see, but isn't this the coat the gets the bugs, droppings, protects from UV and all that? Seems like it would be tougher than that. Strange how things really work. I never thought detailing was, so, well, detailed. :)
Click to expand...

You are correct, but it would be worse without the clear coat.
 
ShowCar said:
Oh. I see, but isn't this the coat the gets the bugs, droppings, protects from UV and all that? Seems like it would be tougher than that. Strange how things really work. I never thought detailing was, so, well, detailed. :)
Click to expand...

Well... its a double edged sword... tougher to damage... tougher to correct as well and vice versa
 
You must log in or register to reply here.
Back
Top