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Old 02-09-14, 03:39 AM   #1
Fumbles22
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Dealing with scratches

Hello,

I've got a few scratches on my bike. I have lots of nicks from gravel on the tubes that connect to the bottom bracket, chipped paint on the front forks and a huge gash along the top tube. The scratches that have gone down to the metal have rusted over.

I plan to get some touch up paint to go over them (or at least go to my local hardware and car stores and ask if they can match the colour), but I have a few questions.

1). Do I need to get rid of the rust before I coat it in touch up paint? I don't want to sand it since it could damage the paint around it.

2). Do I have to lacquer over it? Some touch up paint doesn't seem to require lacquer, but should I lacquer over it anyway?

3). How do I deal with scratches to the lacquer, but not the paint?
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Old 02-09-14, 05:34 AM   #2
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1). Do I need to get rid of the rust before I coat it in touch up paint? I don't want to sand it since it could damage the paint around it.
Yes. If you paint over rust, you'll have a mess within a year. You need to remove as much of the rust as you can by sanding. Do this carefully to minimize damage to the surrounding paint. One trick I use is to wrap the sandpaper around the "point" of a 1" x 2" pink pencil eraser. That provides a nice point for sanding in the scratch. If you do it right you will also feather the edges of the existing paint which you want to do anyway before applying the touch-up. After sanding, treat the spot with a rust "converter" (you can find a variety of brands at the auto parts store). This will chemically seal the surface and hopefully prevent new rust from forming under the touch-up.

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2). Do I have to lacquer over it? Some touch up paint doesn't seem to require lacquer, but should I lacquer over it anyway?
By "lacquer" I think you're referring to the clear coat (which may or may not actually be lacquer-based). Automotive touch-up paint is generally a lacquer formulation and will have good gloss without the need to apply a clear over it.

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3). How do I deal with scratches to the lacquer, but not the paint?
If they're really noticeable, sand them down until you hit the color coat (try not to sand to bare metal) and touch-up normally. You can get clear-coat touch-up paint, but it's really hard to get good results with it.

Note that the key to touch-up painting is what you do after applying the paint. You will generally need to apply several coats of touch-up to each chip and scratch in order to "build up" above the level of the original paint surface. The result will be a lumpy ugly blob that looks almost as bad as the chip/scratch. Now you need to grab a sanding block an some wet-dry sandpaper and wet sand the spots to smooth them out and bring them flush with the original finish. Start with 800 grit and work down to 2000 grit as the spot starts to blend with the original paint. Lastly, hit the now dull but smooth spot with some polishing compound to bring back the gloss.

As you can imagine, this process is a lot of work, so unless this is a rare or vintage frame where you're trying hard to preserve the original paint, disassemble and take the frame to your nearest powder coater to have it sandblasted and powder coated. Cost will likely be under $200 and you'll save yourself at least 8 to 10 hours of labor vs. doing high-quality touch-up work.
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Old 02-09-14, 08:16 AM   #3
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You can easily remove the rust with one of this firm's products: http://www.eraser.com/fybrglass-brushes-and-erasers/
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Old 02-09-14, 08:47 AM   #4
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I fiddled with this recently too: admitting the original paint was scratched and chipped but wanting to cover the bare metal and arrest further corrosion. +++ on the tiny bits of sandpaper. I smoothed the end of a 1/4 inch wooden dowel and used double sided tape to stick fine sandpaper or wet-dry automotive paper to that end. Very controlled sanding with little overlap onto good paint. +++ on rust converter too. I like the outcome. My 1980 was most likely painted with lacquer originally so touching up with lacquer was my route. I scoured the auto parts stores and car lots to find a matching color and failed. I also did not want a spray can for this real detailed touch up. I know many folks had used nail polish for this but none of those colors matched.

Then my wife chimed in "just mix two colors to get what you want". I had no idea you could and women often mix nail polish to get non-stock colors. Flat forehead slap. I needed an almost black metallic so I bought black and silver. I did trial and error a few times on a cat food can lid, keeping notes (2 drops of black and 1 drop of silver? No, how about 3 black and 1 silver, etc). I found a good enough match that repaired the scratch and looked fine from 3 feet away but close inspection revealed the repair and where the original paint was. That seemed appropro. I used the steps Kopsis offered above for the final finish and that too gave good results. I'm riding the bike now. Oh, the nail polish bottles were $0.89 at the grocery store. I always let the nail polish dry a full day before sanding which I think was a good idea. I've used clear nail polish to dot rust converted spots on chrome bits too which should help there. I don't plan to ride these bikes in the rain.
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Old 02-09-14, 09:53 AM   #5
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Emery cloth is more pliable than sand paper and should allow OP to take out rust without damaging too much surrounding paint. Just wrap it around a finger.

Auto parts stores, not hardware stores, are the place for touch up paint. The color selection for autos is quite extensive.
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Old 02-10-14, 03:21 AM   #6
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hit the now dull but smooth spot with some polishing compound
Does car wax qualify as "polishing compound"?

I had a go yesterday sanding the rust down. Unfortunately, I didn't have any sandpaper so I wrapped tin foil around the end of a pencil. It worked quite well. For some reason I seemed to scratch down to the metal, but when I wiped it over with a wet rag to get rid of the dust more rust showed up at the edges of the scratch. I think it's absorbing the water, or i'm wiping the dust into it, one of those two.

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this process is a lot of work, so unless this is a rare or vintage frame where you're trying hard to preserve the original paint, disassemble and take the frame to your nearest powder coater to have it sandblasted and powder coated.
I only paid 30 for the bike and i've spent about 100 changing the wheels, brake levers and brake cables. I don't want to spend too much money!

Also, i've got some decals (or stickers?) on it that I can't seem to find on the internet.

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Then my wife chimed in "just mix two colors to get what you want".
I didn't know that either. If I can't find anything good at the automotive shop, i'll try this. My other bike is white which made it much easier to find something that matched!

I'll post some pictures of the scratches later on today. The more I look at the frame, the more I seem to see!

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Now you need to grab a sanding block an some wet-dry sandpaper and wet sand the spots to smooth them out and bring them flush with the original finish.
EDIT: Why should I wet sand it? What does wet sanding do that dry sanding doesn't?

Last edited by Fumbles22; 02-10-14 at 08:01 AM.
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Old 02-10-14, 11:52 AM   #7
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Does car wax qualify as "polishing compound"?
What you want is "rubbing compound." Some automobile waxes include rubbing compound, but it's better applied separately. It should be available at any automotive store.

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Old 02-10-14, 12:38 PM   #8
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EDIT: Why should I wet sand it? What does wet sanding do that dry sanding doesn't?
Wet sanding floats the paint and metal particles away from the surface of the emery cloth keeping it usable. Dry sanding will clog fine grit papers and cloths rendering them useless in short order.
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Old 02-10-14, 01:14 PM   #9
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If it's just small,light surface rust from scratches and chips,a pencil eraser will get rid of it without messing up your paint.

Nail polish comes in a million colors,you should be able to find something close.
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