Denny Anspach <danspach@...>
Andy Carlson has it just right in advising the use of a standard long-set epoxy to use as a filler choice; and to aalso avoid the 5 minute type, except in extremis [my term!].
An easier epoxy to use is an epoxy designed to be a filler, i.e. epoxy resin already filled with vinyl microballoons, or microfibres. These filler-resins are much lighter in weight, and are much easier to sand. I am still using for this purpose two small "sample" jars (resin and hardener) of very light weight sculpting epoxy handed out at the 2000 NMRA San Jose convention. Like with all epoxies, if the resin becomes stiff and turbid with time, just place the resin container in very hot water for a period of time, and the resin then becomes reconstituted (if that is the word) for another couple of years.
Something very much to keep in mind is that the polyester and epoxy-resin-based fillers set without shrinkage, while the solvent-based fillers always have the potential to always shrink to some extent: the more solvent, the more shrinkage (a cautionary note to those "thinning" putties).
All that said, I still use Squadron putty for tiny jobs where waiting overnight for handling is or would be a pain. I too also despair (kind word) at the shrinkage.
Denny S. Anspach, MD