Al Reynolds wrote:

Anyway, I am building a pergola using the designs
on http://www.pavingexpert.com/featur07.htm

I noticed that the posts are approximately
2.8m long, but only about 0.5m is in the
ground. For fence posts I have always been
told that a quarter of the post should be in
the ground, and this is less than a fifth.

It shows a 2.8m post burried to give a min height of 2.1m, so you have 700mm
in the ground, more than enough for a pergols I would have thought. Don't
think you will find 2.8m posts though, they tend to be 2.1, 2.4, 2.7. 3.0m.

Also, would it matter if the holes were tapered
slightly so they get narrower at the bottom?

Hire or buy (about £17) a post hole digger
http://www.wickes.co.uk/invt/501584&bklist= You wouldn't believe how
effecitive & easy they are.

Also, I will probably use a post fix concrete
like Hanson PostFix or Blue Circle Postcrete
because I have too much money and not enough
experience of mixing mortars. Do you have
any views on whether either of these is a
superior product?

Sorry to disagree with Phil L, but these products are excellent & well worth
the money. I use Wickes Postcrete http://www.wickes.co.uk/invt/221100 one
bag per post. Sets in 10 mins & gives a very strong fixing.




--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257