Here's a summary of two of my replies to Wagner on the subject, [OT] but
still of interest to many tech-picsters.

I can confirm good success with epoxy resins.
I made my own windsurf board with this technique, it is
important not to let large mass of resin cure against foam due to
thermosetting heat.   Epoxy resins are often supplied with dosage
dispensers and it must be mixed in the correct quantities (unlike wide
tolerance of polyester resins)

Use fridge to keep extra quantity from immediatly setting, also surface
sets slightly waxy and so should be washed/cleaned after cure. you can
add bulk and viscosity to mix by addition of fillers, titanium dioxide
colours white and adds surprising
viscosity.   Building industry uses TiO2 with concrete to act as a
strength
enhancing catalyst.

The one I use(epoxy) is used in fiberglass boat manufacture and repair,
there is a two part system resin and hardener. Usually the mix ratio is
either 4:1 or 5:1.  I like the "West System" because they have a range of
dispensers in the form of a pump top, on is placed on the base resin and
one on the hardener.  The hardener
contains amines and although far less stinky than polyester, physical
contact
over a period of years will cause a cumulative poisioning effect.   *Use
disposable gloves*.

Epoxy resins are approximately 3 x the price of Polyester, but have much
better
adhesion qualities.

NOTE: if using to encapsulate electronics then:
1) beware of thermosetting, large thickness of resin will become very hot
and may self destruct, you must use a slow cure mix for low [surface
area/volume] spaces.
2) check fillers carefully for resistivity before adding, ie: do NOT add
carbon black as a pigment, the epoxy will not sufficiently insulate the
solids.
Regards,
Graham Daniel.