newshound wrote:
If the post is well and truly rotten below ground, you could :
remove that rotten wood. Then you should have a fence-post :
shaped hole. OK, might not fit perfectly but a little bit of :
fettling might be enough. If needed use stones, sand, wedges :
to stabilise the post and make it vertical.

For 60cm? That's going to be bloody hard work.

Let me just rp this --

I have done the "chisel out" thing for one post hole - it was hard
work & took a few hours. I used a sturdy metal tube I had lying around
(I think an old curtain pole or similar) and hammered it as far as
possible (typically ~ 5cm) into the trapped wood, then pulled the pole
out, so removing a cylinder of wood; then repeated. One it was mostly
clear, I chiselled the remains stuck to the inside of the concrete.
This was also hard, owing to the confined space inside the concrete
(if I'd had a really long chisel-like tool, this step would have been
less hard).

The wood wasn't rotten all the way down, only maybe 5cm at most, even
though it had rotted through at ground level; making it much harder to
do than it at first seemed. If I had to do another one, I'd probably
do it faster - though I'd guess it'd take at least an hour, even with
practise. A larger diameter tube would have helped, but you wouldn't
want it to break and get stuck.

#Paul