"Matt Langenfeld" writes:

Well in keeping this in the spirit of friendly information sharing we
have started....isn't talc a very heavy alternative? Are microbaloons
not a bad idea for structural fillets?

Talc does nothing but add dead weight.

As far as micro-balloons for structural fillets are concerned, depends on
what you define as a "fillet".

If it is simply a fairing putty used as a gap filling glue with a fillet
formed by a popsicle stick, that is one thing, if you are trying to bridge
say a 1" wide fillet, that is quite another.

For small fillets, NBD, for large fillets, cover putty fillet with a piece
of glass and wet out with epoxy.

As an example, the bulkheads in my boat were installed with a fairing putty
fillet covered by a piece of 24 oz DB glass, about 8" wide to bond them to
the hull.

HTH

Lew