Has any one ever attempted to install a wooden fence post in a PVC socket?
After removing my old fence posts, digging new holes and treating the timber I cannot bear the idea that the fence may only survive 5 years. To concrete or not to concrete seems to be the main question. Is it possible to have the best of both?
Imagine a 160mm PVC pipe secured in the ground with an external concrete collar coming to 2" or so above ground level. The inside of the pipe remains empty, except for the base which is filled 100mm with pea gravel to permit drainage. Inside the PVC insert your 4"x4" post and then fill and tamp with sand and/or pea gravel. Finally seal the top with whatever suits.
Attached is a drawing to aid my idea. In order to keep the fence post dry it is argued drainage is required, however all to often I have read that anything other than concrete is not secure in windy conditions. Perhaps this idea permits drainage next to the pipe but also gives the load spreading and stability of the concrete foundation.
Best thing yet is, to remove the post use a vacuum with a narrow extension and extract the sand and gravel. Then simply pull the post out.
The pipe and concrete are permanent so installing a new post is simple. If the idea does not work I believe I can just replace the sand and gravel with concrete. Perhaps a quick wipe with oil inside the pipe would give me a releasable mould in which the posts could be extracted with the inner concrete section leaving the PVC pipe, but I am not sure of the pullout force of 600mm of concrete in a PVC tube.
I also plan to paint the underground sections of the timber with bitumen paint in order to help prevent any water ingress to the wood. I do not think I want to paint the end grain, as it will prevent water egress. Hence, I suspect I will use end grain preserver.
One possible problem I can see is that the 100mm post in the 160mm pipe does not give ample room for support and tamping. That said, re-tamping inside the PVC tube is an option. I have already bought the posts - but perhaps 75mm posts would have been a better size for this idea.
The second possible problem is the cracking of the PVC pipe if the top is not well supported.
So please feel free to brainstorm with me about the possible pro's and con's of this installation method. So far it is just an idea.
Well the first trial post is complete. I should have put more concrete around the pipe, as 2" is a bit too little. Tamping a 4" post in a 6" pipe is doable. The post is solid and when I pull and push on it. So all in all so far a success but only time will tell.
The fence sockets are done and the posts installed. On top of that I have great news for other fence researches: a comparable test case.
My neighbour has just installed a fence of the same size in the same soil using the same timber but in concrete holes. The only variables are my use of bitumen around the bases and the PVC sockets. I will ask them if the posts have gravel at the bottom or if they used a concrete cup. Otherwise the race is on - who's will rot first?
As for the PVC socket, I increased my dug hole diameter and the posts are as solid as ever. In fact I would argue that my holes are the same if not smaller than my neighbours.
Please be aware if you attempt this method, I recommend painting the PVC as well otherwise it will go brittle form the UV light despite being PVC-U. Also I gave up on the sand and pea gravel - nor does tamping matter, jut pour the pea gravel in the hole - it stiffens up the post immediately, only a light tamping is needed. Lastly - make sure your PVC sockets are plumb!
The attached pic still needs the retaining wall built up around the posts. These sockets are 1000mm long, 400mm up and 600mm buried in concrete.
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