seagoat wrote:
I've got small hair cracks at fillet between the deck surface and
cabin side. It happened because there is a lot of putty with no
fiberglass layer on the top on it. It is painted with epoxy primer
(heavy coat) only. I like to add one or two layers of fiberglass using
epoxy. The deck, side cabin and the putty are polyester based.
My question is: should I sand the surface completely out of primer or I
can apply epoxy/fiberglass on the top of primer?

If you sand off the primer, you know it will work. If you don't sand it
off, it may not. It's your call, but I'd suggest breaking out the sander.