In article ,
Dave W writes:
Should you even be thinking of concrete in the first place? My
neighbour's fence has keeled over because two of the fence posts have
rotted in the concrete. According to several web sources this is not
uncommon, owing to water seeping down and staying there to rot the
wood.

Yes, if you put the posts into concrete (or into the ground),
expect them to start failing after about 5 years.

She will be having a man in to dismantle the fence enough to be able
to dig out the large lumps of concrete. The man said the existing hole
in the concrete was too deep to drill out the old wood. While my
neighbour is saving up to afford the enormous cost, I am going to try
and drill out the wood using a 460cm x 18mm auger I got off ebay.

If the concrete is substantial, cut a metapost spike short, and
hammer it into the old stump without removing any of it. You can
get repair metaposts specifically designed for this, but they're
harder to find - I've only ever done it with the standard spikes,
having cut the spikes shorter.

Maybe you would be better using Metposts?

He is, well concrete spurs, which is the best solution IMHO when
starting from scratch, although my 25 year old metapost fence is
still doing fine, but the metaposts were better quality 25 years
ago (the make was Fensock, which no longer exists).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]