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I completely sandpapered my bike a few months back and repainted it with a coat of primer first, and then matt black. The paint was sprayed only after sandpapering the bike with the appopriate gritt so as to make sure that the primer would stick great.

With the original paint, my bike hardly got scraped too much and too badly, but now, it is easily scratchable. The pure metal is visible as if the primer and the matt black simply were peeled off (where the bike got scratched).

What could I have done so differently to make it so much more scratchable than the original factory paint job?

More Info

  • I sandpapered the bike clean and wiped it down with rubbing alcohol as suggested (I don't remember where).
  • Avoided touching the frame before the painting.
  • Sprayed a coat of primer.
  • Once dried, sprayed the matt black paint.
  • The paints were not at all sprayed heavily to make the paint peal off, and not too lightly either.
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1  
What paint did you use? –  andy256 Apr 16 at 13:18
    
Many (most or all?) factory bikes are powder coated. Read up on Wikipedia for more informaiton. –  Kibbee Apr 16 at 13:21
1  
@Kibbee I don't think that's true for most road bikes and I know quite a number of touring and mountain bikes that are painted instead of powdered. –  arne Apr 16 at 13:51
    
You may have used an incompatible primer. Is the bicycle steel? –  Batman Apr 16 at 15:42
1  
This is what paint does. Depends a lot on the quality of the paint, but pretty much all spray-can paint is pretty soft. It does, however, harden over time -- so after maybe 3 weeks it should be harder than after the first few days. But if the paint and primer are coming off and leaving bare metal you probably used the wrong primer, or applied it incorrectly. –  Daniel R Hicks Apr 16 at 19:40

2 Answers 2

up vote 5 down vote accepted

Commercial paint jobs often use heat-baked enamel, with multiple coats (not just undercoat and topcoat), and finished with a clear top coat.

The baking process produces a really tough, well bonded coating, and the clear topcoat (as well as being tough) produces a nice finish that hides scratches.

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3  
And many are painted, as @Kibbee says, by the powder coating process. –  andy256 Apr 16 at 13:24
    
Hmm, this does make sense... Thanks @andy256! –  Bravo.I Apr 16 at 16:34

Since OP said the bike was Aluminum, we should note some things:

  • Painting aluminum almost always goes wrong when done at home.

  • Upon sanding, often sand particles are embedded in the aluminum (sand blasting likely doesn't help). Chemicals are the way to go for stripping aluminum frames.

  • You need a different type of primer (etching primers specifically intended for aluminum), such as this Rust-Oleum Automotive etching primer. You typically follow this up with another compatible primer.

  • Powder coating / doing this professionally will probably the way to get it to actually work.

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