Nasty rash!

Are there any rivets in that joint? Looks like there's a couple towards the back of the mast in that top picture? if so, I'd be worried that they aren't properly insulated, and you've got some 'orrible galvinic effect going on there.

Whatever the cause, you're going to need to strip back to redo it. be careful doing this, you need to avoid damaging the fibres. If you're stripping back and you do reach the fibres, and the resin still looks like that, then, um, that's a very bad thing.

That's pretty ugly, how old is it? That last phto clearly shows the problem extending along the fibre twills, which could be a cause of concern.

The boat is a fairly early one - 873, not sure if the mast is original, it was refinished about a year ago by the previous owner.
Been sailing 600s for several years now, so have seen and heard all about the problems with metal sleaves in the angel masts.
I'm just wondering if all the effort of stripping back and reapplying is wise without sorting the problem- Any ideas how much someone like Ashdown marine would charge to strip, re-rivet and re-finish the mast?

Ok so whats the best fix here?

- Get it professionally stripped and re-riveted?

- Strip the flakey areas and re-lacquer?

- Don't look up!? (would an insurer consider this lack of maintainace if the mast were to break?)

Thanks for the advice so far!

It looks like the badly effected areas are near joins in the spars, and areas with fittings. It looks like the area may not have been properly prepared last time is was re-laquered and subsequently moisture has got in at the joins and fittings. The moisture will run along the fibres and when it freezes will expand lifting the local lacquer off of the carbon. Once warmed the ice will melt and it will carry on running along the fibres. As Jim says the corrosion usually occurs on the metal fittings not on the carbon.

The fix is to scrape off the old stuff and re varnish with International two-pot varnish. When you scrape and sand the old stuff off take it down until all the current coating goes a milky white colour, clean it up with a bit of acetone and then apply your new coating. The trick is to get right into the corners of fitting as this is where the problem has arisen. Slapping an extra thick coat on in these areas may look good initially but wont help the underlying problem, so make sure you prepare it well.

Paul