Preparing cast iron keel for coppercoat

[Ric]

View attachment 33034My boat has a cast iron keel which has been encapsulated in a 2mm layer of (I think) gelcoat by the factory. Most of this layer is still very well attached and is in good condition, so I don't want to disturb it. However, in a few small areas it has flaked away, exposing the cast iron. What might be the best way to prepare this for copper coat?

I intend to put on multiple layers of 3M aluminium rich Scotchtcote epoxy primer under the coppercoat, but should I first grind and sand back the flaked areas? Or should I build them back over with epoxy mastic and then smooth back before applying the primer?

 

[vyv_cox]

My keel was grit blasted and epoxied before applying Coppercoat, which has been pretty successful. Within about two weeks of launching I sailed over a partly submerged buoy made up of polystyrene blocks tied together with wire, which generated a large scrape in the keel down to bare metal. At the end of the season I ground the scrape out with an angle grinder and applied five coats of West epoxy, then five of Coppercoat.

Four years later I am seeing a few pits where the original treatment is breaking down but my repair looks as good as new.