Al Reynolds wrote:
Hello all,

Haven't posted here or even lurked for more
than a year, and my news server is showing
over 300,000 unread messages! Good to see
a few familiar names though.

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.

Do you think this is because there isn't as
much lateral force on a pergola (due to wind)
so it does not need as much to stop the post
moving as with a fence? I guess with all the
braces the pergola could be pretty much
free-standing, so the main thing is to keep it
in the same position in the ground.

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

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 for all the questions! Thanks in
advance for any help you can offer.

Al Reynolds

Don't buy named concrete or mortar mixes, just use plain old cement at £3 a
bag, for each 25kg bag you'll need 2 sand and four stone, you can mix it wet
or dry, litterally no water at all and it will still set rock hard through
natural absorption.

I should imagine 500mm is ample, it's not a swing / gatepost / fencepost
after all and shouldn't be under too much stress.....I would be inclined to
get as much preservative into the legs prior to concreting though...leave
each one resting in a bucket of creosote overnight or something similar,
also place a few inches of concrete at the bottom of each hole first so that
the end grain isn't sitting in wet soil, then concrete almost level to the
top of the hole, thus protecting almost all of the timber below ground.