Jay,


Not sure I have ever heard of fiberglass that was not fuel resistant.
Most glass resins I have ever heard of are polyester based and
definitely hold up against most fuels (chemists please feel free to
chime in). More likely there was a blending/curing problem or they used
some old resin that had a contaminant or moisture problem. If the
catalyst proportion was too low and/or the temperature during the cure
was low, there may have been a very slow cure period. Once fuel or other
solvents gets to glass that is not fully cured, it will start to
delaminate (as you described). However, even in this case, the mix
usually hardens way before you ever gas up since it takes some time to
prepare for paint, paint, mount, and then refuel. Most I have seen a bad
mix take to cure is 12 hours or so. If it took any longer, one usually
starts over and scraps the first attempt.

Another possibility is that the tank actually contained fuel during the
process. Don't laugh. I have seen similar situations. Fumes from the
fuel will disrupt curing and cause all sorts of ills as they get
absorbed in the resin.

You wrench used epoxy-based filler? New one on me. I never knew that was
approved for use on fuel tanks. After sanding I'll bet the old
fiberglass job looked perfect too! Time will tell.


Mike

Jay Honeck wrote:
Got a problem here, and I'm wondering if anyone else has run into it before.

Five years ago (or so) the previous owner of our Cherokee 235 repainted the
fiberglass wingtip tanks.

Apparently he had an automotive body shop do the fiberglass work, and around
the filler necks they used a fiberglass that was NOT impervious to gasoline.
Thus, the fiberglass resin turned kinda mushy, and little chunks of it
started coming out. Paint wouldn't stick to it, and it just generally
looked like crap. Eventually it could have become an airworthiness problem,
as the filler necks might have come completely out of the fiberglass.

My A&P has now dug out all the gooey fiberglass, and replaced it with a
gasoline impervious epoxy-based filler. After sanding, it looks PERFECT,
and I have just purchased the paint ($80 a PINT for Imron now!) to paint the
tops of both tips.

Question: In another aviation forum, someone mentioned that the gasoline
vapors can actually go THROUGH fiberglass, and get at the underside of the
paint. It then works on the paint from the underside, softens it, and the
surface starts to break down.

If this is true, then what I have done will only solve the problem right
around the filler necks. Has anyone ever heard of this? Did I fix the tip
of the iceberg here? Is there a better "fix" for the problem than what
we're doing?

Thanks!


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