Your summary of CBM1 is correct.
While CBM page 1-9 indicates you can use Q-Cel for final finishing, it is not
preferred.
It is typically used on foam, prior to layup of fiberglass cloth. The
second sentence of the last paragraph on page 37-3 says to use Expancel.
Expancel
is lighter, more flexible and easier to sand; which is why it is better.
You should not need to buy any glass microspheres.
Expancel should be mixed very dry to keep it light. To be consistent, we used
the
same amount of Expancel to resin in every batch. We used a 10:1 ratio by volume.
This is important if you have to go back and refill if the batches are
not consistent, it is difficult to sand evenly as some sections are harder than
others (due to more or less epoxy in the mix) so you can get bumps and dips.
It is possible that the filler delaminated because it did not adhere properly to
the fiberglass. To prevent that, we used a clean dry cloth (old sock) to rub
a very small amount of resin on the fiberglass just before spreading the
Expancel.
Yes, the photo you attached shows pretty thick filler. For some reason we did
not receive the original post with photos of the damaged areas so we dont know
where that came from. Filler used to blend two areas where one is proud of the
other can be somewhat thick, so areas where fairings are glued to the wing
near the wing root can have more buildup than other areas. Normally it should
not be as thick as the piece in your photo.
Since Expancel may be hard to find in the US, some people have used West System
407 / 410 products or Poly Fiber Superfil. We have not used either, maybe
others
can comment.
Jim & Heather
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