A pair of ST rotors from a GTR track customer that were severely oxidized and were considered as "discard" or "rebuilt" condition. We put them on to our shop car (2016 Mercedes CLS550) to test with sintered pads (trackabel street compound).
After these damaged ST rotors were installed, the car vibrated so violently (at any speed as the brake pedal was applied) that make it un-driveable, so next day the passenger side rotor was removed and replaced back to iron.
ST CCM-X rotor (Passenger side) removed after one day on sintered pad.
ST CCM-X rotor (Driver side) after 10 days of normal street driving with some occasional hard stops.
Detail view - A more continuous band of metallic finish can be seen.
Since ST discs are made from continuous fiber, the damage is in a "patch" pattern (than Brembo's chopped fiber which is more of a uniform and consistent manner), which makes the restoring process harder (larger spots to fill in) and longer in this restoration process which is somewhat expected.
We have also found that the wearing pattern of pad and rotor surface are in groovy pattern than Brembo's disc in a non groovy surface which coincides to how the respective carbon fibers are structured.
These pictures from the test can not represent what you will actually see with eyes unless taken by pro-photographer, however the effect of rotor surface restoration via the transfer of pad is evident and can definitely be felt by the driver, being the vibration amplitude is progressively getting diminished as the rotor surface looks better (more smooth shining area than spotty patches)
The long process and trouble involved perhaps not worth for a consumer than have it re-furbished, however the point of this test is to demonstrate the effect of a sintered pad can do to a CCM rotor that's severely damaged, better yet is to start the sintered pad in the beginning and avoid it, or mend the rotor with sintered pad before gets so bad.