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Here's a video about this method. http://www.youtube.com/watch?v=9A8i6mouohw
I stopped using it a while ago, I care about my customers and myself.
when you dig up the lump of concrete you generally end up with a much bigger hole and you might have to use a lot more concrete as shown on the pictu...
this is a way to re-use the concrete foundation
The spacers will keep a uniform gap between the post and the bag
the socket bag is specifically designed for the purpose of fitting a 100x100mm (4"x4") section fence post. The bag is fairly robust and 900mm (3ft) lo...
fill the gap with dry sand and pat while doing it to create a grip between the socket and the post
the material used is off cuts of insulation pipes, this is to separate the silicon from the dry sand
seal the top with silicon to keep the water out.
insert the post into the ground and concrete it in.
to extract the post, cut the silicon seal and suck the sand out with a vacuum cleaner
now you have a hollow foundation and can replace the post re-using the dry sand.
should you need to remove the concrete foundation completely due to ground movement or change of plans, it is still far easier to do so as the hollow...
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Where to get large amounts of silicone? and where to get the bags from?
The video does a good job of showing the various ways of extracting an old post, and implies that extracting this post would be easier. I don't understand why that would be. Yes you don't have to hoist the concrete, but you still have to get a grip on the post and pull it out somehow. Seems like the traditional extraction methods are still needed.
As for reinstalling a new post if you ever have to: that was really glossed over in the video. If you have removed the post and vacuumed the sand, how do you put a new bagged post in without ripping the bag on the concrete? And if the new bagged post goes in that easily, wouldn't it be loose? Or do you set a new, bare post and then just fill with sand around it?
Are posts supposed to last longer using your method? It would seem like they would if they are kept dry.
the method requires more work but not considerable more work. the diamater of the socket filled with sand is about 190mm=7&1/2 inches so if you dig a standard hole 1ft wide that leaves a gap between the post and the ground of about (300-190)/2= 55mm=2inches. Personnaly I do not use ballast and cement but sand and cement for the job either dry or wet according to the job. The added material cost per post is about £5 (maybe 8$) but replacing a concreted broken post is considerably more, typically I charge at least 100$ because of the labour and extra materials involved.
the post socket is 900=3ft long to cover any conditions but can be cut to size to fit a 500 or 600mm (2ft) deep hole s I normally do.
Traditional extraction methods are not needed.When the sand is extracted there is nothing gripping the post and it comes out with ease.
The bag is quite robust and can be reused as it stands. I concede that accidents might happen and a new bag is needed. That is not a problem as you insert the bag first into the hole , a bit of sand then the post and fill it with sand which will expand the bag
As you said keeping the moisture out of the base of the post makes it last longer. Should any water penetrate anyway you would not be in a worst condition the the traditional post and concrete method and as a precaution you can always add boron salts at the base of the socket. The water would dissolve the salts with would penetrate the wood thus preserving the wood.
I have been using this method for 3 years and no customers has called me back to replace any of the posts.