In situations regarding resins, paints, when you are in doubt, its best to try out something first on a sample.

So in your case I would search for a piece of a broken mast from the same sort. (f.i. in the shop of a cat-dealer on the coast). Or from an unlucky catsailor in your neighbourhood.

P.S. And even if you are an expert in resins and paints, that still is a wise method....