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Scratch in bicycle frame down to raw aluminium - problem?

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Scratch in bicycle frame down to raw aluminium - problem?

Old 05-11-16, 02:28 AM
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dja1
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Scratch in bicycle frame down to raw aluminium - problem?

Noticed a small gash on the paintwork on my frame after it slid along a wall - nothing significant but the aluminium underneath is definitely visible. Could this pose a risk of developing structural damage? As I am aware that aluminium is prone to corrosion.

I read that nail varnish can possibly be used to touch up small flaws like this?
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Old 05-11-16, 02:57 AM
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There are many different aluminum alloys. Some are more damaged by corrosion than others, but in general, they resist the elements much better than steel.

Are you particularly exposed to salt? Road salt in the winter? Marine environment?

If not, I wouldn't worry about it, although there are some individuals who's sweat is also damaging to frames.

Paint over it if you wish, even clear enamel. But, your frame will likely get more scratches in the future.
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Old 05-11-16, 03:04 AM
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From what I know, aluminium oxidizes on the surface that is open to air. However, unlike steel, the surface oxide acts as a protective layer against further oxidation - almost as good as painting over the scratched part yourself. I wouldn't worry.
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Old 05-11-16, 04:17 AM
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Throw the bike out. It is ruined
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Old 05-11-16, 06:07 AM
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Originally Posted by Slaninar View Post
From what I know, aluminium oxidizes on the surface that is open to air. However, unlike steel, the surface oxide acts as a protective layer against further oxidation - almost as good as painting over the scratched part yourself. I wouldn't worry.
That is correct unless the area is further exposed to corrosive agents like sweat or acidic solutions that dissolve the oxide and re-expose the bare metal surface. A little clear or colored touch-up paint can't hurt. Yes nail polish can be used, but automobile touch-up paint from the auto parts store is even better, especially if you are trying to match a color.
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Old 05-11-16, 07:58 AM
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The only concern is that surface oxidation can end up allowing moisture between metal and paint in the area around a gouge. This is why it's imperative to touch up any scratch down to metal in a car. Though as mentioned previously, this shouldn't be anything more than a cosmetic concern under normal conditions. The drivetrain would probably rust first anyway.
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Old 05-11-16, 08:01 AM
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Clean it dry it and throw some clear coat on it to seal it. As others mentioned aluminum is not as prone to rust that pentrates the surface. However it is a point were paint will be weak, and begin to chip. Cover it up with some clearcoat to seal it.
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Old 05-11-16, 08:04 AM
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Originally Posted by dcwldct View Post
The only concern is that surface oxidation can end up allowing moisture between metal and paint in the area around a gouge. This is why it's imperative to touch up any scratch down to metal in a car.
And most cars are made from steel not aluminum.
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Old 05-11-16, 08:52 AM
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If thats a problem, my mountain bike is in serious trouble.
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Old 05-11-16, 09:07 AM
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Find a nail polish that closely resembles the colour of your frame and add successive layers until the thickness matches that of your original paint.

From a distance of a few feet, or in motion, no one will ever know.
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Old 05-11-16, 10:57 PM
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Originally Posted by rpenmanparker View Post
That is correct unless the area is further exposed to corrosive agents like sweat or acidic solutions that dissolve the oxide and re-expose the bare metal surface. A little clear or colored touch-up paint can't hurt. Yes nail polish can be used, but automobile touch-up paint from the auto parts store is even better, especially if you are trying to match a color.
I believe this is correct, but what is the amount of acidic solution that would harm the frame? Here's my experience:

I ride a 1996 steel frame MTB. The frame is full of scratches. Ride it in the winter, with lots of water, snow and salt. No rust destroying it yet.

I've also had a few aluminium frames. But never had an alu frame for more than 4 years to be able to tell if rust would destroy it. However, all my bikes are full of scratches - I fall down a lot and don't bother to be too careful about scratching a frame - never had any rust problems. No paint chipping etc.
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Old 05-11-16, 11:20 PM
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Originally Posted by rpenmanparker View Post
Yes nail polish can be used, but automobile touch-up paint from the auto parts store is even better, especially if you are trying to match a color.
Have you looked lately? It's amazing how many colours of nail polish there are!

I've also gone to hobby stores for unusual colours. I had an old steel Merckx frame that was an odd yellow. I found a train caboose colour from olden times that matched perfectly.
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Old 05-12-16, 04:47 AM
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Originally Posted by bakes1 View Post
Throw the bike out. It is ruined
+1
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Old 05-12-16, 12:03 PM
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Originally Posted by Bob Dopolina View Post
Find a nail polish that closely resembles the colour of your frame and add successive layers until the thickness matches that of your original paint.

From a distance of a few feet, or in motion, no one will ever know.
+1

I have used this method on my aluminum frame and it works very well.
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Old 05-12-16, 12:50 PM
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Originally Posted by Bob Dopolina View Post
Have you looked lately? It's amazing how many colours of nail polish there are!

I've also gone to hobby stores for unusual colours. I had an old steel Merckx frame that was an odd yellow. I found a train caboose colour from olden times that matched perfectly.
Yeah, I knew that was going to come up. Hell, I could match any bike I have ever had just from Mrs. rpen's selection of nail polishes.

Mentioning the auto touch up paint was just a reflex reaction. I have been using that stuff for so long, it is what I just naturally think of. But it is getting to where the nail polish may offer easier matches.
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Old 05-12-16, 12:58 PM
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Originally Posted by DosWheelsBtr View Post
+1
+1000
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Old 05-12-16, 05:05 PM
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Here why I like the liquid paints for this.

Orient the scratch on the frame in such a way that it is parallel to the ground.
Then place a small drop of paint on the bare surface inside the scratch or chip and let it FLOW to the edge of the original paint.
Don't brush it over the edge and onto the original paint. Let it flow until it MEETS the edge of the original paint.
Let it dry and do it again until the depth of paint matches up.
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