Aliminium tarnishing and discolouration...

[Cyclopathic]

I've got an ali' frame unpainted but protected by a clear laquer which stops the discolouration asociated with aliminium. Over the years it has started to look a bit scrappy and scratched in places. I noticed that on a piece of frame where the laquer had gone completely that I was able to polish it to a near mirror finish with some brasso. Really the little patch looked almost like chrome.

Now then my schoolboy sense of style has always wished for a shiney chrome bike, something that would absolutely gleam in the sun. If I were to remove the laquer (comes off very easily with nitromors) I could polish the beast up to look fantastic. What I need to know is if this is wise or if it will leave the frame open to corrosion and weakening? Obviously without the laquer it will eventually tarnish and that to keep the mirror finish I will have to polish it every so often which is fine but I'm not going to do it if it could lead to any more significant damage?

My other dilema is that I also want my bike to look old and knackered rather than shiney and new so that it doesn't represent an easy £20 for a thief to get whacked out on goofballs. It gets me soooo mad. One just can't have nice things.

 

[swee'pea99]

Your second dilemma is unsolvable - if you make it more nicer you make it more scrote-attractive. As for the first, you won't weaken it. Aluminium doesn't rust like iron or steel - it tarnishes, then the tarnish protects it from any further damage. But I suspect you'd need pretty regular polishing to keep that chrome look.

 

[tyred]

Like Swee'pea99 says, polishing aluminium is a bit of a waste of time as it tarnishes over very quickly and that coat of oxide protects the metal from further oxidation.

If you want to go down this route, it would need some sort of clear coating to protect it and it would need to be applied PDQ before oxidation sets in again. My concern would be the residue from the polish making it unlikely that a coat of laquer would stick to it properly. I'm sure it could be done, but you'd need to choose your products carefully.

 

[fossyant]

Frame alloys are a little different from 'component alloy'. I've stripped the anodising off a set of cranks years ago, and all they need is a light polish every so often - solid alloy billet though !

Frame alloy will oxidise and cause the 'furring' if not protected. Totally non-structural but looks a mess. Does have a habit of getting under paint on alloy frames though, and making the finish un-even or even come off.

 

[snailracer]

Pure aluminium tarnishes as previous posters have described, however bike frames are made of aluminium alloys which have no natural self-protective oxidation mechanism. Protection against corrosion is provided by lacquer and other industrial coatings, which vigorous polishing removes, leaving the alloy to weaken and fail if exposed to the elements and road salt.

 

[Cyclopathic]

All of the advice so far has solved my dilema about wanting a shiney bike that is more atractive to scroats. I have decided against going down this path and will decorate and personalise the frame with some paint using brushes not spray cans. It gives a more rustic, less comercialy atractive finish.

Now my problem is what sort of design to put on it and what is the best sort of paint. Unless someone has a good reason why not I'll just go for a hard wearing, outdoor gloss that won't cost a fortune. Never again will I go down the path of stripping, sanding, spray can primer, spray paint (3 coats) and spray clear laquer. I ended up spending more than it would have cost to get it powder coated and baked and although it was a bloody good job if I say so myself it is still very weak and scratches easily.

Sooo, anyone got any tips on hand painting designs on a bike?

 

[tyred]

I've only ever repainted steel frames but I've found Japlac Enamel works well for me. It flows well and if you use a good quality brush, you'd hardly see any brush marks.