Topic: Tiny bumps in paint
in Forum: C3 Body
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My Vette, which was repainted in '93, has tiny bumps all over it. Most are very, very small, which I am guessing were dust particles settling on the body before the paint was applied or during application. Occasionally is a bigger bump, more like the size of a small grain of sand under the paint. This spring, I was planning on color-sanding to try and eliminate as much of this as possible. My guess is that will take care of the tiny ones, but not the larger. I was wondering if anyone had advice and no, I don't plan on repainting.
Also, the paint appears to be base coat - clear coat, as I got out some all-in-one cleaner/polish/wax and a white cloth and hit a small section and got no black pigment on the cloth. Wish I could more accurately describe the bump sizes... Any advice?

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It's not uncommon to get some trash in a repaint. Most shops buff that out before a car goes out the door.
Typically, the clear gets most if not all the trash, for some reason, the base doesn't seem to. If there is enough clear on the car, ultra fine sanding and buffing will take care of the problem. The bad part is, you really have no way of knowing just how much clear you have to work with so a "burn through" is very possible. It's really a gamble.
Another issue is what the little bumps really look like. If they look like tiny bubbles, you may have a "solvent pop" issue. Regretfully there really isn't much you can do to correct it other than repaint the car. Solvent pop usually shows up fairly soon after the car is painted though.
Typically, the clear gets most if not all the trash, for some reason, the base doesn't seem to. If there is enough clear on the car, ultra fine sanding and buffing will take care of the problem. The bad part is, you really have no way of knowing just how much clear you have to work with so a "burn through" is very possible. It's really a gamble.
Another issue is what the little bumps really look like. If they look like tiny bubbles, you may have a "solvent pop" issue. Regretfully there really isn't much you can do to correct it other than repaint the car. Solvent pop usually shows up fairly soon after the car is painted though.

For a guy like myself with no pro body shop tools or supplies, what materials would you recommend? I was thinking a sanding block like those hard rubber ones made for a 1/4 sheet of paper with maybe 1500 or 2000 grit sandpaper would have a better chance of grinding off the spots than a buffing cloth, as the cloth would conform more to the shape of the bumps than grinding them off. Make any sense? If so, I will start with the finest grit I can find and only move up to a coarser grit it not working.
Do they make sandpaper finer than 2000 grit?
What is the most coarse grit you would recommend I go to (if necessary) without risking burning thru the clear coat? I know, not an exact science, but your educated estimate is better than my guess!
Do they make sandpaper finer than 2000 grit?
What is the most coarse grit you would recommend I go to (if necessary) without risking burning thru the clear coat? I know, not an exact science, but your educated estimate is better than my guess!
I don't think I'd use anything tougher than 1500 on a 12 year old paint job. Then move to 2000 to take the 1500 scratches out. Follow that with buffing, then polishing. Black is a very unforgiving color so take your time. The block is a good idea, but you have to be careful with the contours. By all means, take your time.

Also watch those bumps and high points as you sand. More important the areas around them. A common mistake is to sand the bump off without paying attention to the area around the bump. You can sand through the surrounding area while looking at the bump. Easy mistake.
There is a thing called a nib file you can get at body supply shops. It's a small block with a file surface on one side. It purpose is to "shave" those bumps off. Done carefully, a nib file can make the bump flat with very minimal damage to the surface. The surface can then be sanded or buffed more easily then sanding the entire nib off.
There is a thing called a nib file you can get at body supply shops. It's a small block with a file surface on one side. It purpose is to "shave" those bumps off. Done carefully, a nib file can make the bump flat with very minimal damage to the surface. The surface can then be sanded or buffed more easily then sanding the entire nib off.
Did your car get striped down to fiberglass before your repaint? was a gel coat applied? If the sanding was not proper before the base coat then you can see all kinds of bumps all over the body.
"I Love all Corvettes! LifeTime Member #60..Terry"
Unfortunately, I have no specifics on the paint job, as it was done by my brother when he owned the car. My brother is no longer with us, so all I have is an invoice that tells me he paid very little for it. At 5 foot. the paint doesn't look bad at all. I can see the larger bumps in good light, but I really only feel the smaller ones.
Thanks for the advise so far and any more to come!
Thanks for the advise so far and any more to come!
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Lake Oswego, OR - USA
Joined: 12/29/2002
Posts: 355
Vette(s): 1968 Corvette T-Top Coupe, 427 L71, Rally Red Exterior, Saddle Interior
Its very important to make sure you use a degreaser/silicone remover before you do any sanding. If you don't you just push any contaminants back into the paint and you get nowhere fast. Try 1500 first and if not doing the trick you may have to go down to 1200 or 1000, but I don't recommend it. Remember, your clear coat is not very thick.
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