Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
I am not sure what reflecting water means to be honest. But car body
filler is completely impermeable if thats what you mean, being comprised
of polyester resin (the sort fibreglass boats are made out of) and a
mineral filler - think its mica, which is not noted for its hygroscopic
properties either ;-)

Some 'fibreglass' car body fillers are/were porous - if my books on
bodging car bodywork are to be believed. Wouldn't mica be difficult to
sand?

Its not a particlarly hard compound. Porous car body filler is a bit of
a pain..I suspect you may be thinking of body PUTTY, which is more a
soft cellulose based air drying thing.