Yes, but I think that has to do with what will bond to what, and in which "state"
Both Polyester and Vinylester gelcoats will stay tacky, when exposed to air, and Epoxy will not bond properly to those in a tacky state, unless they are specially formulated to do so (Like the GC50 gelcoat)
Adding wax additive to handle that will definitely prevent the epoxy from bonding to the Gelcoat--
Also the point of using Epoxy and CF for the mould is to make it dimensionally stable (no shrink) that usually means using an all epoxy setup. But, maybe one could use the Unimould Gelcoat, with epoxy backing, it may be worth a test
The EC tech guys may have some input to this ?
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