Bubbling paint on carbon and alu

[ishaw]

So, a frame purchase on a whim arrived today, pics before purchase showed the bubbling so knew what I was getting.

What's the cause of this? From what I can tell, it looks like mudguards have been rubbing in the affected areas.

What's the solution? I'm thinking rubbing down and trying to touch in the areas, frame wasn't too expensive but I'd like to smarten it up. Paint is not going to be easy to match, a couple of colours. Red should be ok, might get creative and perhaps mask off some of the original colour and paint round it, but the white is not quite white, slightly metallic so going to be hard to match I think.

 

[jim haseltine]

Both alloy and steel are susceptible to galvanic corrosion where bonded to a carbon composite. Water accelerates the chemical reaction and can also wick along any exposed fibres and temperature variations can then cause the moisture to expand and contract creating micro cracks in the resin. There's no permanent solution but rubbing back the affected areas to a solid base and then repainting should delay the process.

 

[mamadirt]

Rub it down with fine grit sandpaper and prime first with white(or a light colour). I use basic artists acrylic paint as it's water based and won't hurt the carbon - easy to mix and build up layer by layer, sanding back just a little after each application. Gentle T cutting will give it a bit of a shine but I'll probably end up lacquering the Manitou Carbons I'm currently restoring as I don't want the whole lot to disappear at the first sign of a bit o' grease or fork oil

 

[ishaw]

On closer inspection, the bubbling is around areas where the bottle cage and brake mount on the bridge.

I'm not averse to tackling, though getting a paint match will be tricky as it's a metallic off white. Frame has red areas so thinking of adding some extra red if I were to rub down and paint.

I'm in two minds. It's not too bad, but if left as is, I'm sure it will get worse. What is going on under the paint to cause the bubbling, and will it, if left to continue, cause issues with the alloy frame strength and ultimately eat the frame to breaking point?

It's a decent enough frame I've got all but the front mech to build now, so want to either sort before I build up, or leave it it's not going to be a problem further down the line.