The short answer
The quickest fix for a broken timber post is a concrete repair spur – a short concrete post concreted in beside the old one and bolted to it. Alternatively, prop the panels either side, unscrew them from the post, cut out the old post, dig out or bypass the old footing, set a new post and re-fix the panels.
Most posts fail at the ground line, while the part above ground is still sound. That's why a repair spur works so well: it replaces the weak section without disturbing the fence.
Option 1: a concrete repair spur
Spurs are cheap, quick to fit and very strong. They're ideal when the old post is rotten only at the base.
- Straighten the post and prop it upright
- Dig a hole beside the post, about 600mm deep
- Place the spur and concrete it in
- Once set, bolt the spur to the post through pre-drilled holes
Option 2: a new post in place
If the post is rotten higher up, or you want a cleaner finish, replace it. Prop the panels on both sides with timber or blocks, unscrew or unclip them from the post, then remove the old post. If the old concrete footing is hard to remove, you can dig a new hole slightly to one side, though you may need to trim a panel.
Set the new post in concrete or postcrete, check it with a spirit level, and re-fix the panels once the concrete has set. See how deep fence posts should be.
Concrete posts
Concrete posts rarely rot, but they can crack or lean. Replacing one usually means sliding panels out of the slots, so you can't always avoid moving panels. Sometimes a leaning concrete post can be re-set without replacing it – see how to fix a leaning fence.
Preventing it happening again
Use posts treated for ground contact, add gravel to the bottom of the hole, and slope the concrete away from the post. See how to stop fence posts rotting. Or get a quote for fence repairs.