usually, a simple scuff up sanding and a wipedown with acetone would be sufficient for barrier coat to adhere. A fresh barrier coat would require that same sanding and wipedown to stick properly.. A hard antifouling is usually a lot more particular about what it wants to stick to, so if you are thinking about hard AF, another barrier coat with first coat of AF applied while epoxy barrier is still not fully cured usually gives the best adhesion.. If ablative AF, you could scuff the barrier, wipe down, and go with AF.. I am speaking in generalities, so ya probably need to look at the application instructions of the particular barrier and AF that you are considering.
