I'm not sure but I seem to remember that POR-15, a common metal gas tank sealer works on epoxies too.

idk if this is what you are looking for but a local supplier by me just posted this on their site. Might be worth a call to see if it fits your application. Sorry EC, I know this is another vendor, Im not promoting just trying to help.

Made a few of them and if you have the correct resin there is no problem..  The resin I use has been used in Indy car for years..

Personally I would look into making a custom bladder for the inside of the mold, like pretty much all fuel cells have.  That is what the ferrari F40 has.  It is safer solution than trying to do something that you think might work because some guy on the internet did it.  

I am using an ethanol resistant resin to both seal the inside of the pre-preg tank and initially I have made the first few bases using the resin. Not done any long term tests but the supplier does supply it knowing it is used in an environment where it is subjected to ethanol continually. 

The slight down side to the resin if used to actually make the parts is the part is quite flexible. Used as a sealer this is fine. used in the tank base again not too much of a problem as the rest of the fuel tank is pre-preg and if the base has a little flex it is not a problem. 

I forget what it is called... Need to get more sleep and sniff less cleaning products I guess.. But the supplier is Alchemie. The down side if you buy a small quantity is postage as it is £20 I think even if you only have 1 kg.... I am not too far away so drive over to collect it... 

Here is to bringing life to an old post.

It's not finished yet! LOL.  Too many projects on the go and working a lot more now.

However the initial tests i did were fine on silicone based DOT 5 race brake fluids.  Nothing nasty in those fluids so no surprise. The final plan was to use a tank lining anyway and normal DOT 4 glycol based fluid didn't eat through the brake fluid liner I used.

I don't intend to run the fluid against just the normal infused epoxy.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

How did your brake fluid tank hold up warren? Brake fluid is nasty to normal paintwork have you had any troubles with yours?

We would unlikely have any more resources than yourself and the power of the internet.  We have approached our resin manufacturer about the issues of both fuel resistance and brake fluid resistance as it is a common question these days.  Very little data exists on the resistance to ethanol's probably because it's not been tested.

The basic petrol has never been an issue, hence the abundance of composite fuel tanks both in automotive and marine usage. Its purely the relatively recent issue of ethanol.

You will struggle to get information out of the high end motorsport or aerospace as they tend to use special coatings or bag tanks so won't encounter the same problems.

Until someone develops a fuel resistant resin, then tank coatings are your only realistic option.  I can't see a massive demand for such a resin when coatings that work already exist. Most high end motorsport is using the flexible kevlar bag tanks which use a fabric coated with a special rubber, so again I can't see motorsport driving a demand for such a resin either.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Hi Warren - thanks for your reply. About a year ago I read about a Phenolic resin that was allegedly Ethanol proof. I think it was called Christic 99 but I can't find any record of it now. It's possible I imagined it and it could have just as easily been a vinylester or polyester resin, but from what I remember of the curing process it was most likely Phenolic. If I didn't imagine it, I'm not sure whether whether there is a gel coat that works with Phenolic resins. Possbily a polyester coating would but with reduced fire retardation, which I'd be prepared to live with if it was ethanol proof. Would you have access to any resources to be able to research this further please?