Originally Posted by GDS
This is a quote from one of my partners, a Pulsar builder/pilot and an engineer with 20+ years working on aerospace composites:
"You do not want to use a glass tank bare. Depending on the particular resin system used, some may have less resistance to ethanol dissolution and may allow the glass and resin to gradually breakdown. You have to coat the inside wetted surface with a blocker like Jeffco 9700, an epoxy based sealer that is immune to ethanol. I have a glass tank on my Pulsar which has used only mogas with 10% ethanol for over 5 years and absolutely no breakdown of glass because of the Jeffco."
Jeffco tank sealer is good stuff. the lancairs use this for tank sealant. It is easy to tell a tank that doesn't have it, eventually it will end up weeping pretty bad.
I would use it for any composite fuel tank, doesn't matter if it is vinylester or epoxy