normanwisdom wrote:
Car body filler too hard to clean up easily, traditional putty much
better as it can be pressed, moulded, rubbed etc whilst still softish,
and is very durable once painted. So that's the first trick you've
missed!
Hardly a trick. Putty is not a good filler. Small amounts will dry out
very quickly and, if it's only the paint keeping them in place, you have
ideal conditions for further rot.

Nonsense. Putty has been successfully used as a filler for hundreds of
years and if painted over reasonably soon (within a few weeks) it sets
hard and lasts forever.

The idea of painting it quickly is to stop it setting. Once dry, it's
too inflexible to be of any use as a wood filler.