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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.
  • 1
    What paint did you use? – andy256 Apr 16 '14 at 13:18
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    Many (most or all?) factory bikes are powder coated. Read up on Wikipedia for more informaiton. – Kibbee Apr 16 '14 at 13:21
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    @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 '14 at 13:51
  • You may have used an incompatible primer. Is the bicycle steel? – Batman Apr 16 '14 at 15:42
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    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 '14 at 19:40
20

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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    And many are painted, as @Kibbee says, by the powder coating process. – andy256 Apr 16 '14 at 13:24
  • Hmm, this does make sense... Thanks @andy256! – Ihsan Apr 16 '14 at 16:34
13

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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2

I've painted a number of bikes now and I always run into the same problem. I was advised to use etching paint on bare metal before priming, but this did not help. It's really frustrating because you spend a lot of time preparing the surface and painting, then the paint scratches the first time something hard (or even not so hard...I got a scratch just accidentally banging the bike frame against a wooden door) touches the new paint job.

I've come to the conclusion that this is just the way it is with home-made paint jobs.

If I was restoring a really nice/expensive bike, I would get it professionally painted, but this reduces the amount of pride you have for you bike.

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  • Completely disagree - this should not be "the way it is for home-paint jobs" Rather its a failure of the paint system. eg: I have a spray can of car exhaust manifold matt black paint. On handlebars etc, looks like normal paint but flakes off on the first gust of wind, or a sharp look. This paint requires baking "through normal operation of the engine" so I use a cheap home hot air gun to heat the part up to 150-200 degrees C , and its totally like rock after cooling. A light sand, coat of black gloss spraypaint and left for three days and the part looks new. – Criggie Jun 23 '16 at 23:05
  • Surely using a hot air gun would just remove the paint ? As is one of the uses of these guns?? – Roisin Ellison Jun 14 at 7:12
  • @RoisinEllison Possibly - it depends on the paint. I used engine paint which needs hundreds of degrees C to set. A power-coat would also be set by heat and not come off with hot air. Common aerosol paint would probably soften and come off with heat, but a 2 part spray mix would not. It all comes down to what paint, how it was applied, and cured, and surface preparation. Oh and sometimes there's a clear lacquer on top for protection, which should be "compatible" with the underlying layers otherwise it comes off really easily. A good clearcoat helps durability too. – Criggie Jun 14 at 10:59

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