Longest slotted concrete posts

I read a post here from 2007 asking about the longest concrete posts available for a rear fence in a 4 foot drop ["Long concrete fence posts"]. Thermo & JohnD replied. You advised that some suppliers had 10 foot lengths.

We have exactly same problem and want to use concrete gravel boards with, ideally 6x6ft, wooden panels in slotted concrete posts. JohnD's reply to OP said....

"... and they would need a very deep root. If the fence is not very long (I mean if you don't need a lot of them because of cost) you might use a steel as is used on motorway fencing."

Clarification on that last bit please... Does it mean use steel posts instead of concrete OR anchor/root the long concrete posts with some sort of steel spike or sleeve? And where do you buy them? I'm lost, so any help will be very welcome. Thanks all.

Either would work, assuming you can easily bolt the concrete to a steel post (would need to be a hefty size though)

I'd be tempted to go with some small section rsj's. Slide the concrete gravel boards down between the flanges, and wedge somehow. Or bolt a section of angle iron to the web, to make a slot just slightly wider than the gravel board (usually 50mm)

you could then bolt a length of timber in the groove of the beam, on both sides, and nail the fencing into this, as you would a normal timber post.


These posts will need sinking deep and concreting in. Older sized 100mm x 100mm RSJ's will be ideal for this.

Thanks very much Deluks, that's very helpful.

My mind was fixed into using concrete posts and gravel boards, but your suggestion of RSJs, or similar, as post anchors allows the use of concrete gravel boards where it matters (to help retain soil when that area is levelled off) and combines them with wooden posts & panels above soil level.

I'll certainly explore that idea. I'd have to find seven anchor posts in all ... then hope that the roots of the enormous conifers on the rear neighbour's side don't get in the way.... (any suggestions for drilling suitable post holes where hefty roots might be encountered?).

Thanks again for your time and trouble. Much appreciated

Roots will be a pain, cut through them if you have to. If they are massive trees as you say then they'll survive. A gardener pal has a really old wooden handled spade, that has half the blade ground to a sharp edge for slicing through thick roots. Works very well.
He keeps it in his house as it was a family heirloom