I have a couple of steel frames which have what look like snail trails under the paintwork in places. They are slightly raised are thin and are random in their direction. Presumably they are a form of corrosion, but how dangerous are they? Also one of the frames I was going to have resprayed and another I was going to paint my self, but should I use a particular preparation or is sandblasting the best thing for it?

No real answer to the question…they are rust veins and probably are just on the surface, but they will grow. You are going to repaint both frames just inspect the tubes after you have removed the paint.
Personally I can not see a problem using a sandblaster, if the tubes are significantly rusted that they can not take a blast, the frame is shot anyway, or requires expensive repairs. What frames are they?

I’m guessing Filiform Corrosion from your description, and the fact that it is under a painted surface. Shouldn’t cause too much concern in the short term but I would be looking at a frame strip, dip and re-spray if I wanted it to last.

Here’s some info.

Cheers for the replies.

One is a Cotic Soul mk 1 and the other is a Raleigh Optima road bike from ’98ish. The Soul is worth a powdercoat, but I’m not sure about the Raleigh. It is a nice looking frame though and perfect for a round the town hack bike.

It is a nice looking frame though and perfect for a round the town hack bike

Then I wouldn’t worry about it too much. Filiform corrosion is a surface corrosion and shouldn’t effect the structural integrity unless it gets really bad.

Those thin lines are never serious, it actually takes quite a bit for steel to rust through or weaken significantly. So as long as you’re getting them repainted they’ll be fine.

Cy at Cotic said not to blast an old Soul I had. He said to dip/chemically strip, then lightly blast as a key for new paint. He said blasting would be too aggressive for the tubes.

Once again, cheers for the replies, looks like I’ll look for a place with chemical stripping 🙂