Aluminum frame bubbling paint

[retrobate]

Remove the oxide with abrasives (wear a mask) & assess how much the tube wall thickness has been reduced, if you think it is significant bin the frame if not do the follwing.
Open up the hole with a drill to remove stress raisers to reduce the risk of cracking.
Treat the bare metal with Alocrom 1200 (or whatever the modern equivelent is).
Fill the hole & any pitting with Devcon or JB weld.
Etch prime & then paint.
Ride and enjoy until it cracks somwhere else, it is a Cannondale 30 year old aluminium alloy frame after all

 

[d8mok]

Or option B - buy a replacement frame for less than the cost of the bits needed to make this right.

Last solid m600 frame I sold went for sub £20. Just buy a good one and bin this.

 

[Twozaskars]

Please cut it two and just get rid of it, stop someone hurting themselves.

 

[retrobate]

I've read that you should rub down all the bubbling paint and remove the aluminum oxide and then either primer these areas or polish them.

Would you agree this is best course of action?

If a m900 is what you want the options are
Best option

Or option B - buy a replacement frame for less than the cost of the bits needed to make this right. And inspect the frame regularly for cracking

2nd best option

Remove the oxide with abrasives
Open up the hole with a drill to remove stress raisers to reduce the risk of cracking (if not a hole blend out pitting).
Treat the bare metal with Alocrom 1200.
Fill the hole & any pitting with Devcon.
Etch prime & then paint. And inspect the frame regularly for cracking

3rd best option

Remove the oxide with abrasives
Open up the hole with a drill to remove stress raisers to reduce the risk of cracking (if not a hole blend out pitting).
Prime & then paint. And inspect the frame regularly for cracking

4th best option
Just ride it, And inspect the frame regularly for cracking

Please cut it two and just get rid of it, stop someone hurting themselves.

Options 2 & 3 do require some engineering judgement but lets not get carried away, aluminium oxide has a volume far greater than the parent metal it came from (I dont recall the exact figure but 9-10 times rings a bell - dont quote me though) so its possibly not as bad as it looks. The good thing is that the corrosion is on the outside so at least you can see what you are dealing with.
At the end of the day Its a 30 year old ally frame, it and any aluminium frame will fail due to fatigue at some (undetermined) point, maybe not in your lifetime but eventually.
The greater risk is more likely to be 30 year old lightweight aluminium handlebars

ps Inspect regularly for cracking

 

[greencat]

Would none of you even use the bike for riding on the roads & canal paths (so no jumps or drops) around London at w-ends?

I used to regularly commute in London, and the state of the roads definitely contributed to one of my frames cracking.

 

[Twozaskars]

If you’re going to rub it down (in fact, I think you owe it to the world now - in the interests of science and safety or whatever) you should not use your usual steel wire brush, use a brass or even better a poly wheel in your drill like the example below. That way, if you do repaint it and put it back into service there will be no traces of iron left embedded into the aluminium to start any galvanic corrosion.

5 x Poly Strip Discs Wheel Rust Paint Removal Abrasive Drill Angle Grinder 50mm~ | eBay

5 x Poly Strip Wheels Discs. Mounting on a drill pin 6mm. Paint Removal. Due to its structure and high elasticity, the non-woven fabric enables cleaning of flat surfaces as well as surfaces with more complex shapes.

www.ebay.co.uk

 

[retrobate]

If you’re going to rub it down (in fact, I think you owe it to the world now - in the interests of science and safety or whatever) you should not use your usual steel wire brush, use a brass or even better a poly wheel in your drill like the example below. That way, if you do repaint it and put it back into service there will be no traces of iron left embedded into the aluminium to start any galvanic corrosion.

5 x Poly Strip Discs Wheel Rust Paint Removal Abrasive Drill Angle Grinder 50mm~ | eBay

5 x Poly Strip Wheels Discs. Mounting on a drill pin 6mm. Paint Removal. Due to its structure and high elasticity, the non-woven fabric enables cleaning of flat surfaces as well as surfaces with more complex shapes.

www.ebay.co.uk

Good point. I like these

3M SC-DR, Non-Woven Disc, 5527, 50mm, Medium, Aluminium Oxide 7000000751 | Cromwell Tools

Reinforced Scotch-Brite™ web designed for cleaning and finishing on all metals. Leaves a burr-free surface for painting and coating for removal of light rust, oxides and coatings. 7000000751 | Cromwell Tools

www.cromwell.co.uk

but wet & dry paper would be fine.