My friend just bought an O'Day 34 and we need to have a bottom job done, The keel is cast iron and I have read a bit on the owners' sites but I'm still lost. The boat is not pulled yet and I don't know what we will find when we do.
I have sandblasted a keel on a Beneteau before and it required no fairing. Depending on the condition of this keel, it may require removal of all paint (I hope there is no fairing compound) and prime/paint. If we try to patch over rusty spots I don't know the paint/fairing compound used prior, I could be at risk of patching with a non-compatible material.