Dont use bondo. It expands when wet, and your fairing will become unfair.
Use micro or glass balloons.

"jcassara" wrote in message
et...
I am in the process of repairing a rotted deck core. The
area is about 6 sq ft and is built up with polyester cloth.
Is there an additive to thicken polyester resin to use as a
fairing compound? Can automotive Bondo be used? Will fairing
compounds as found at West Marine or Bondo stand up to
typical deck activity or will they crack?

Any info would be great!

John