epoxi over polyester

If you read my comment, the request to leave the polyester to outgas/cure was given by the various resin suppliers to Sunseeker/Marine Projects etc (over 1000 boats per year, ave size 16m) NOT by the paint supplier.

"covering their butt" is a metaphor for stating a fact that prevents/minimises risk of failure (getting your bum well and truly beaten...often with the financial equivalent with a barbed wire wrapped bat).

Any excessive unreacted styrene (and peroxide) can interfere with the chemical reaction in epoxy system. A physical key does not stop this byreaction and possible failure.

Suppliers normally promise you the earth. When they don't, you should normally listen. Excessive sensitivity to known modes of failure is not something you would normally accuse them of. Customers get real mad when something goes wrong and you turn around and tell them it was known problem but they had to take the risk for some reason.

Sure the chances are perhaps unlikely but they happen. And i am talking with experience of failures seen in field with various resins and various coatings (ie solvent free, water based and solvent based from various suppliers)

My comment was just trying to help the guy minimise his risks. If he had no commercial reason to take risk, don't take it. It's like speeding in your car. At the end of the day you make your own decision.

ps straight expoxy is no less sensitive to this by reaction with styrene than a epoxy paint would be. The adhesive strengths are to all intents and purposes the same. Arguably paint adheres better due to better surface wetting properties. And the "paint" recommendation covered both Epiglass epoxies and the International Paint Gelshield osmosis solvent free epoxy system. (and also Hempels equivalent)