Concrete Fence Post Cracked Or Snapped

What's happening?

Concrete fence posts fail differently from timber ones and the difference is the reinforcement inside. A concrete post carries steel bars close to its faces; if the concrete cover over that steel is thin, or a crack lets water in, the steel corrodes, and corroding steel expands and pushes the concrete off from the inside. That is the classic pattern: a rust-stained crack running along the post, then a piece of the face spalling away, then the slot edge going. Frost does the same job faster, freezing water inside an existing crack and levering it wider each winter. A clean break straight across is usually impact — a vehicle, a falling branch, or the sudden shock of a panel being wrenched in a gale. The important point for a homeowner is that a concrete post is not repairable in the way a timber one is: once the steel is exposed and corroding, the post has a limited life whatever you fill the crack with.

What usually causes it?

• Corrosion of the internal steel reinforcement expanding and spalling the concrete off the face
• Insufficient concrete cover over the reinforcement when the post was made
• Frost action opening an existing crack wider each winter
• Impact — a vehicle, a falling branch, or a panel wrenched hard in a gale
• The slot edge chipped or broken away, so the panel is no longer held
• Movement of the foundation, putting bending load on a post designed to work in compression and bending only up to a point
• Overloading from added trellis, boarding or heavy climbers

When should you call a fencing and gate installer?

Call a fencing installer if the post has snapped, if the crack crosses the post, if reinforcement is visible, or if the slot has broken so the panel is unsupported. Bring it forward where the fence borders public space or carries a gate. It is also worth having the whole run looked at — concrete posts on a fence tend to be the same age and the same batch, so one failing with exposed steel usually means others are on their way.

What will the fencing and gate installer actually do?

• Inspect the post and the rest of the run for cracks, rust staining, spalled faces and damaged slots
• Distinguish reinforcement corrosion from impact damage, because that decides repair against replacement
• Support the panels either side, remove the failed post and break out the old foundation
• Set a replacement post to the correct depth in a properly sized concrete collar
• Fit a repair spur alongside a post that has failed at ground level but is otherwise sound, where that is appropriate
• Reinstate the panels and gravel boards square to a string line, and report the condition of the remaining posts so the run can be planned rather than repaired piecemeal