Vinylester resin used to be the preferred resin for aircraft gas tanks and I understand from a marine repair specialist that it is still the resin of choice for offshore boat tanks (the built-in ones). Granted, the chemistry of marine and aviation gasoline is a lot different than skanky pump gas, so this may not be a valid comparison and a lot of aircraft and boats also use diesel and Jet A fuel as well.
Regarding epoxy resins, I would check with your resin supplier and tell him exactly what you are using the resin for - ie, building a gas tank. He may be able to find the most suitable resin for your needs from his sources.
Regardless of the resin used to build the tank, there are a couple of things you could do to enhance the fuel resistance. One is already mentioned: put a coat of Caswell novus phenolic epoxy resin tank liner in it just before "marryup" (according to Caswell's chemist, with a new vinylester tank, you have a max 7 days after layup before you should do the scuff and solvent thing) and then pour another load in the tank to seal the bond line afterwards.
Another item that was always recommended to me by my composite materials supplier but I rarely see it mentioned is the use of "veil" on the inside of the tank as the final ply. It builds a resin-rich inner face of the tank. However, it shouldn't extend into the bond line - if it does, do a brutal solvent wipe / scuff / solvent wipe to remove it before bonding.
I was involved in a Lancair 4P project and subsequently a 2 place carbon fiber jet. In both cases, the specified fuel tank sealant was from Jeffco - of the novus phenolic modified epoxy family as I recall.
Take precautions with all of this stuff - especially epoxies. I just finished repairing a customer's 'glass tank and in spite of my best efforts, I have about a 2 inch circle of contact dermititus to contend with.
Hope this helps - or maybe just confuses the issue even further? Myself, I use derakane vinylester resin with a coat of Caswell before marryup.
Pat Cowan,
Pacomotorstuff
