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I am building a stitch&glue plywood boat that is coated with fiberglass and epoxy on the outside. I am trying to determine whenever I need to add epoxy primer on top of the epoxy coat before painting. The dealer who I bought the epoxy from says that it is not needed, as the resin he sold will act as a primer itself. I called another store, specializing in paints, and they say that I do need to buy epoxy primer from them to get a good grip for the paint.

I will be using two coats of polyurethane paint.

Can someone clear this up? Is there any practical difference between epoxy resin and epoxy primer? Do I really need to spend extra money on the expensive primer, when I still have lot of resin?

Thank you in advance!

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  • In terms of what is ideal I think this may depend on the exact nature of the epoxy and the paint rather that there being a single rule of thumb you can follow. However most paints will stick to nearly any substrate if a texture is provided for it to cling to (called mechanical bond). So if the surface of the epoxy/fibreglass coating is uniformly sanded and degreased there's a very good chance you'll get a good bond, it may not be the strongest bond possible. [contd]
    – Graphus
    Commented Jun 4, 2018 at 15:59
  • If you want to skip using the epoxy primer it would be advisable to do an adhesion test, see final bullet point of this Answer.
    – Graphus
    Commented Jun 4, 2018 at 15:59

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