Builders have successfully constructed composite fuel tanks using foam/epoxy
since the early 1970s. The secret to building a durable fuel tank is a
thick, well-cured epoxy coating.
To minimize long-term performance problems the following is recommended:
1. Carefully metered resin/hardener ratios is critical to epoxy
performance.
When mixing epoxy for tank coatings, its recommended that a
resin-rich / hardener-lean mixture be used at the outer limits of the
manufactures acceptable mixing range.
This is because excess resin in epoxy matrix is less likely to adversely
affect the physical properties of cured epoxy than excess hardener.
When excess hardener is in the epoxy matrix, it cannot fully react with
the resin and will become suspended in the mixture.
2. Coat all interior surfaces with 4-coats of rolled epoxy. After it
is rolled on, brush the epoxy out to minimize any entrapped air.
Install surge baffles to minimize free surface effect, using generous
fillets and giving them the same 4-coats of epoxy as the rest of the
tank interior.
Any tank openings, such as fill, vent should be oversized and also
receive
4-coats of epoxy. All fasteners should be epoxy bonded in place to
secure
any hardware to the tank or in the construction of the tank.
3. Scrub cured epoxy thoroughly with water and a scouring/abrasive
pad.
This removes any surface contamination, specifically any potential
amine blush that may form on the surface. Amine blush is water-soluble
and can be removed with tap water. The scrubbing action agitates the
surface to help with removal.
4. Post cure at an elevated temperature, 140° F for 8 hours
(after epoxy has cured at room temperature and can no longer be
dented with your thumbnail).
All sizes of fuel tanks have been successfully constructed with foam/epoxy
and used with great results. In testing, various epoxy combinations have
proven to be resistant to various liquids, including gasoline, diesel fuel,
motor oil, etc.
Regarding gasoline specifically, some epoxy combinations are more resistant
than others, however with the increasing use of alcohol and other high-tech
additives, it is unsure how the epoxy will resist them in the future.
Refs: Gougeon Brothers, Inc.; Patrick Ropp
Best Regards,
Larry A Capps
KR Newsletter CD
Naperville, IL
