Andrew Gabriel wrote:
In article ,
mikesmith writes:
With deep holes to fill do people fill with several applications and
let the previous one dry out totally - or one "big" overfill and sand
down when thoroughly dry.

I tend to use one big underfill to within a 1-2mm of the surface
which may well crack as it sets but that doesn't matter, and then
a thin coat polished off with a wet trowel or scraper to match
the surrounding surface. No sanding required.

That is what I do too... any shrinkage cracks are welcome as they help
to provide an extra key for the final finishing coat :-)

Also - I have a box I have had for at least three years - does it go
off (in the past its use by date sense) - I have noticed hairline
cracks in some of the filling I have done.

I have never had a problem with old polyfilla, even when it was stored
in open packages for a few years.

Steve