This was no easy decision, not least because of the many different paint systems that are available. A few years ago I wrote about the varying types of blacking paint, and how to identify them and their uses HERE. Now we have decided to use the 2-pack epoxy coating there are also many decisions to be made on which system within this category to go for. There are 2-pack pitch primers followed by a final 2-pack vinyl black top coat, 2-pack blacking that requires no final top coat, and 2-pack blacking that can be finished off with a compatible final 1-pack coal tar based (Comastic) final coat. None of these finishes can be used over an existing bitumen paint, so that is the reason for the grit blasting, which not only gets rid of all traces of old paint, and rust, but provides a good bare metal ground for the new 2-pack blacking to adhere to.
I had pondered the idea of simply mechanically removing loose material from the waterline before treating with a rust converter and re-painting with the same bitumen finish, but after discussions with the boat yard staff who are going to do the work, who themselves consulted various paint manufacturer's technical departments on my behalf, decided in the end to follow the route we have taken, which is simply the grit blast followed by re-finishing with a propriety brand of 2-pack epoxy blacking to the manufacturers intructions. Hopefully, all will turn out well. I will report on the results and prices in a couple of weeks time when the job is complete.