Once cured, it's just a solid plastic just like a polyester based product and you are getting nothing but a mechanical bond with anything you put on top of either one (paint, gelcoat, etc.).
That is correct Jake, but epoxy has more adhesive power then polyester.
That has to do with the difference in the polymerisation process (the curing) which apply for the epoxy and the polyester resin.
The polyesterharder is only the katalysator and accelarator in the curing, while the epoxy harder plays really a role in the curing and hence in the bonding with the underlying surface!
Besides that the thermal expanding coefficient of both resins are not exactly the same, nor are the mechanical stressvalues. Moreover polyester shrinks while curing.
This leads to the following rules of thumb: epoxy on polyester is better then the reverse and also better then polyester on polyester.
Ofcourse you can have had succesfull experiences with other combinations; but think wise.
