Nigel Graham wrote:
> All filler continues to shrink for some months after initial cure. I
> have seen some beautifully finished wings where the spar and ribs show
> through after six months to a year.
I wonder if what was being observed was polyester Bondo, not epoxy
fillers.
Or possibly Europa's fluffy stuff, which when mixed very dry, seems
more absorbent, creates some long-term effect vis-a-vis some finish
coatings. In which case waiting 6+ months won't work!
The mfr of SuperFil states clearly it does not shrink, and I have many
prime-only parts with SuperFil, the Aeropoxy equivalent, or Europa's
fluffy stuff/epoxy. There is no shrinkage. Ultimate shrinkage of
epoxy resin is in the respective data sheets, so where they say 1%,
epoxy is only a fraction of the mix by volume. Thus .25% or so
shrinkage of the mix I can't believe would be visible.
The post also suggested an 80" sanding spline. On the Mk 1 wings
especially, this will necessarily require more filler. Any improved
visual effect after gloss coat as against a much shorter spline will
be minor. Once the wing is installed, it will no longer be exactly
flat under the 80" spline, a sad fact I noticed after screwing around
trying to get a straight surface under a 72" straight-edge. I can't
recommend it.
Regards,
Fred F., A063
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