"Al Reynolds" wrote in message
...
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


600mm in the ground is enough. Once fully constructed the pergola is very
solid and the posts should not take too much strain. Accurate placement is
the key to successful installation in my experience - you cannot measure too
often. The rest of the job is then easy. Ensure there is drainage at the
bottom and if you can slope the concrete at the top away from the post so
water drains. We used 80% of a bag of Blue Circle postcrete on each post and
a few old broken bricks as packing and it worked really well. The dry mix
method would work too and probably be cheaper. At the risk of being a bit
radical though, I am not totally persuaded that you will need to concrete
the posts in given the minimum loading on them assuming tha you are building
a double pergola.

It is important that cut surfaces are properly treated with preservative. We
bought our pergola as a kit from Jacksons fencing - they are possibly
expensive but worked well and they were helpful. Check pieces are straight
though, and avoid the sell of too many bags of nails to fix it. We had six
bays and used just over one bag of 3" and just over one bag of 4" nails to
complete it.

HTH