On Fri, 5 Jun 2009 18:29:32 +0100, mo wrote:

guy suggested 1 bag of mix per post - but i don't have the bags yet and
i have no idea how much concrete there will be when its mixed!

The same as a bag, the "guy" is suggesting the use of a "ready mix" like
Postcrete not mixing up cemet, sand and agrregate...

As I have just said dig a snuggish hole, not much more than 1" all round
clearance, pop in the post and back fill with the dry mix waggling the
post and tamping down the mix as you go. Having a bit of initial "give" in
the post fixing may well be useful to take up "manufacturing tolerances"
in the panels.

--
Cheers
Dave.