[afc69]

My brake discs seem permanently rusted up or oxidised, which makes the alloy wheels look unsightly. Is it just overspray when washing the wheels that makes them go this way, and does it normally wear off after a short journey - ie braking etc, or is there some kind of barrier or laquer that can be applied?

 

[mikaveli]

Unfortunately, there's no real barrier or lacquer that can be applied - the area the contacts the pad especially - any crap on there will have very serious effects on your braking.

You've got two main options, the first is to buy a more abrasive set of pads - it won't stop rust appearing, but should clear the surface quicker when you drive.

The second option is to buy a different set of discs, either going for a grade of metal that won't rust as fast or alternative materials.

I've heard that some Brembo discs are plated, to prevent rust in non-contact areas, if that helps. Whereas some cheap 'performance' discs are known to rust extremely quickly...

 

[John328i]

If you mean its not clearing after driving, it could mean you have a sticking pad/s or caliper..Or uneven wear on the pads and disc..
As Mikaveli also stated .. Do not use any products on your discs.!