painting an aluminum/carbon frame

Question

I have a frame I would like to get repainted. It is a composite of aluminum and carbon fiber (Al main triangle, carbon fiber seat/chain stays). The carbon fiber is unpainted (maybe a clear coat) and I'd like to keep it this way.

1. Is it easy to sand blast just the Al part? If the carbon fiber gets sand blasted it will just get destroyed, right? What would happen if I used glass bead or plastic bead blasting?

2. It should be no problem for a professional to repaint the Al. Simply mask off the carbon fiber and paint away, right?

Answer 1

Your assumptions are right on, the carbon fiber stays are definitely our biggest obstacle. They prevent you from being able to powder coat the aluminum, the risk of damaging the carbon fiber from heat in the process is too great.

A professional in town should be able to properly mask the carbon fiber and sandblast or glass bead blast the aluminum. I believe glass bead blasting is the preferred option and is supposed to be gentler. Then comes the new paint job.

As usual, Sheldon has quite a bit of information on the subject: http://sheldonbrown.com/paint-prep.html

Answer 2

You're better off not bothering - aluminum should be chemically stripped and carbon should be handled professionally from start to finish [and you need special primers and what not]. The problem with sand blasting is that particles can be embedded into the aluminum. Since you have an interface between the materials, it might be more trouble, or it might not be - depends on how the interface is done [note that the vapors of the chemical stripping process may cause troubles].

That being said, finding a professional who can deal with bicycles is a non-trivial matter with a non-trivial price attached, so unless you're particularly attached to repainting this, its not worth it.