After four years blisters have formed in the paint of my aluminium road bike, namely in the area of the top tube, in front of the seat post; in some areas the paint has already chipped off. Is it possible that the frame is corroded due to sweat and the aluminium affected to such an extent that it compromises the stability; and what about carbon frames?
Reply by Dirk Zedler, TOUR technology expert and bicycle expert
What you describe is not unusual. Not only aluminium frames, but steel frames as well are again and again affected by corrosions underneath the paint. It is seldom that painted surfaces are entirely closed, so that the pores and areas where the paint has chipped off are permeable to sweat and humidity. These corrosive agents infiltrate the paint. Depending on how aggressive the sweat is, the frame starts to flourish and blisters form under the paint. By the time the frame is likely to be affected by corrosion to such an extent that this will compromise the frame structure. We therefore recommend that you sand back this area, remove the corrosion and apply a new coat of paint. As an alternative you can also bring the frame in a specialist paint shop to have the paint removed from the frame and to apply a completely new coat of paint. There are paint shops specialized on wet painting and on powder coating.
Carbon as material, in contrast, is corrosion resistant. There are, however, some products the aluminium components of which, such as bearing cups, cable stops or front derailleur mounts, are affected by corrosion. Therefore, it is important in general to wash the road racing bike regularly with water to remove the harmful sweat. The use of chemical agents is less important, as the salt crystals on the sweat dissolve in water and are rinsed off.
