Another vote for Jeffco fuel tank sealer. Fundamentally there should be no problem with regular epoxy, but I think the Jeffco is a little more flexible and therefore a better sealant, but what do I know? Not that much, in this case.
But ... Jeffco fuel tank sealer *is* epoxy resin. It is called a “high solids content epoxy” and I have *no* clue what that means. But it’s easy to use, a lot of Lancairs have been built using is, it seems to work, and it’s not particularly expensive as airplane epoxy goes. It's also opaque, which helps in the application process. It reveals defects (thin coats, pinholes) more readily than a clear epoxy would.
A couple of things, though. Put on one coat, then wait a little bit (maybe 30 minutes?) until the surface is starting to get tacky. Add a second coat. This will cover the inevitable pinholes, and if you wait until the first coat fully sets up, then you’ll have to wait for it to fully cure, then scuff/sand and apply a second coat. Of course, waiting, sanding and coming back for a second coat is acceptable as well. It’s just a bunch more work.
If you want, you could probably dab the sealer locally where you see the pinholes, instead of a full second coat. But my thinking was that there may be an “almost erupted” pinhole, not yet visible, that will result in a really thin epoxy shell locally, which is likely to fracture and leak over time. So the safe course is to apply two coats. As I recall, that's what the manual recommends, too, but I did this back in 2001 so I don't remember *all* of the details!
Also, the vertical surfaces will need extra attention. The sealant will tend to run down the vertical surfaces and you will see that it becomes rather thin. You will probably want to be there brushing on more sealant, or brushing the slumping stuff back into position, until it starts to cure. (This was more of an issue for the wings than the header tank, as I recall)
Like Randy, I brushed on a coat on the floor where hydraulic fluid will leak someday. I also did a coat on the underside of the wheel wells. The upper surface of the inside of my wheel wells is untreated. I did not do the inside of the cowling. In all of these non-tank places, you only need one coat. Pinholes don’t really matter there. You just want to contain the spill until you can wipe it up. You don’t want to contain the fluid permanently.
Good luck!
- Rob Wolf
p.s. Jeffco Fuel Tank sealer is apparently FDA approved! It turns out that it’s used to seal large food containers, or so I have been told…