The key question when applying a new coat of antifouling paint on a vessel is to determine if the new paint will be compatible with the old one (provided that you’re not planning on completely sand out the previous coating. In such case obviously, you’ve eluded the question).
Nowadays, antifouling paints formulas vary so much in terms of active ingredient that you can easily screw up by applying say hard based paint on a silicone based one, thus compromising the adherence of the new paint on the old one. Practically, that means seeing your precious paint peeling off your hull after 1 week. It would be a shame, especially considering the price you paid for it.
Obviously, if you know that you’re applying the same paint as the one that was used the previous time, things are easy.
Problem rises when you don’t know what kind of paint is there, or when you know what type it is, but some reason, you’re unable to source it again,and you have to apply another type.
Paint manufacturers supplies compatibility charts which can help, and if you’re lucky enough to find the reference of the old paint in it, you can consider your problem solved.
But, as per Murphy’s law, you may probably end up not knowing if Racing from Jotun will accept a coating of Micron 77 from International.
That’s where the barrier coat comes handy: barrier coat are primer paints which will isolate the previous coating from the new one. On top of it, they’ll increase the adherence of the new coat.
All paint manufacturers do market their own barrier coat paint: to my mind comes Primocon from International, Vynil Primer from Jotun, or P-1 from Nautix. I wouldn’t know which one is the best, but I’m pretty sure they would all do the job.
Better safe than sorry.
