old paint or gelcoat...how to I.D.?

[ElBichoMalo]

I was planning to paint my topsides with Interlux Perfection...a 2-part linear polyurethane paint. I have read many times that you cannot use these over any 1-part paints. I am a little concerned about this, because the topsides were very obviously "painted" with "something" by the P.O. The problem is, I'm not sure what the "something" is...it is thick, chalky, and flaking off in some spots, but I really don't have the experience or knowledge to know if this is paint or gelcoat???? Obviously, I plan to sand through the bad spots, but with all of the nooks and crannies and me being a sanding-hater...I'm not confident that all will be removed....hence concerned the 2-part paint might not stick.

Any tell-tale signs to let me know if I am dealing with crappy paint or gelcoat?