[RCSE] LIGHT, Sandable Filler with strength?

[Scobie Puchtler or Sarah Felstiner]

What might I use as a filler on a foam wing that is as LIGHT as possible,
has some strength, but still truly 'shape-able', and 'sand-able'??

This wing will be film covered directly over the foam, so I need something
that I can really smooth out well to cover various cavities in the wing
necessary for routing of wires and some of the radio components, before the
final covering.

I have used microballoons and epoxy, but it is not satisfying to shape, and
comes out fairly heavy, at least when I've tried to mix it. Any tips to
getting this stuff really satisfying to shape and super light? Is it even
possible?

I have used the super-light DAP and Red Devil Onetime, and they fill and
sand great, and are remarkably light, but have TERRIBLE strength if used for
anything but the tiniest fill jobs. On a tape covered wing, larger fills
often break up under the tape covering. Any way to strengthen it?

I'm curious about expanding foam sprays or mixes, but have my doubts about
their ability to be shaped and sanded effectively. Any experience, anyone??

I guess I'd really like to find or mix something that would act as much like
blue foam as possible, so that the fill sands similarly to the foam, and its
easy to make a smooth transition from one to the other.



TIA for your patience with this question, and all the brilliant answers I
know are coming!

Lift,
Scobie in Seattle.

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