UKH

Hi

I have a rotten fence which I have taken down. I have excavated and removed the concrete blocks for the old posts and am now left with the holes. 
The issue I have now is that the holes are not the usual deep narrow hole that are suitable for setting the new posts with postcrete. They are too wide.

The original concrete blocks were very large, wide and I had to dig around them to remove them.

Anyone got any techniques for dealing with this issue. If i try to backfill around the edges of the hole the backfill soil will just fall into the centre of the hole and reduce depth. 
 

I cant dig new holes as the posts  need to be in exactly the same place due to positioning of an intersection and a gate.

thanks.

Shuttering.

Rent an auger and drill a deep hole in the existing hole exactly where you need it, then set post in concrete.

https://www.diy.com/departments/grange-concrete-repair-spur-h-1m-w-75mm/152...

You now have a wide hole so you might as well take advantage of that to keep new post above ground level without any/much more digging. Use old blocks (broken up a bit if necesary) to reduce how much concrete you need to fill hole.

I just got a couple of"post buddies" to try out on one fence post. Might be a bodge but I don't fancy digging out half a dozen posts.

https://postbuddysystem.co.uk/

I know it's too late now, but what I've done before is leave the old concrete in place and use a drill and breaker to remove just enough round the old post. It's slower than just removing the entire lump but it means you only need a third of a bag of postcrete per post and you don't have to dispose of all  the old concrete.

In your situation I would probably just use regular concrete rather than postcrete, using the old concrete broken up as ballast. You do have to prop the posts up while it sets though.

Alternatives to the good suggestion of shuttering from maggot:

Fill the hole with soil and use a whacker to compact it down, then dig your new hole out.   Compacting a filled hole with a manual 10” tamper is a good work out, and satisfying too…  

If the fence posts are square, prop a 2x2 grid of fence posts in, backfill around them and tamp down hard, them remove leaving a hole of the right size for the post and postcrete.

Use a longer preferably hard wood post.

Dig down deep, and back fill slowly and tap it down hard. Using the top of a sledgehammer works well. Hammer in lumps of brick and rubble and it'll be fine.

That's what I've done with mine, they'll takes decades to rot as it hardwood. Water won't get stuck in the concrete and rot the post.

If you are using timber posts, I would not concrete them at all, posts rot much quicker in concrete than if you fill the hole with gravel and tamp them down firmly, that allows the water to seep away from the post.

You’ll be fine backfilling the posts with soil but ensure the depth of the hole is 1/3 the length of the post. Add a little at a time and compact each layer as you go, re-checking for plumb regularly. Keep big lumps of rock and brick to a minimum as they are liable to rattle loose over time, for the same reason do not use gravel. Crushed limestone is great if you have some handy as it will set up really solid, but it’s not essential. 

If you can’t get down to 1/3 post depth then using concrete/postcrete might be your best option. If the ground is really loose knock some shutters together so you can compact the soil around the concrete once it’s gone off. Don’t concrete right to the bottom of the post and ensure the concrete ends slightly above ground level and angles away from the post. Posts set in concrete do rot quicker and there isn’t much you can do about it, larch or oak timber posts will last longer but are pricey (especially at the moment). 

I use type 1 hardcore for wooden posts, compacts nice and tight but still porous.

Dumpy bag is cheap enough as well (around £50 delivered)

My preference is always to avoid using concrete, it just speeds up the rotting of the post and the person who has to break it out will hate you

Use hardcore or soil instead and tamp it down nice and firm every few inches as you gradually fill the holes.

A good method I've seen was to back fill around a piece of drainage pipe then standing the post in the pipe fill around the post with medium gravel. If the post rots then you can hoover out the gravel and replace it.

When setting my wooden posts in concrete I purchased special bituminous bags to wrap the bottom 2ft of post. Any water ingress due to porosity of the concrete should be avoided.

Thanks all for the suggestion. Lots of variety. I now have to pick which to go with. 
I might actually try the no concrete approach. I’d never considered it as a viable option- thought it was something done in the US.

at least it means that if my handywork fails it can easily be excavated and re-done. 

I also visited half the b&q stores and builders yards in glasgow trying to find postcrete. None available. Must be the canal blockage/covid/brexit effect!
 

Yep, no bagged cement/postcrete here for about 3 weeks.