Replacing a fence post in a hole that’s too big – how?!

Hiya, replacing a fence post, 4″ x 4″ with a 5′ fence panel. Post has snapped at the base and there’s a big old lump of concrete in the floor – suspect it’s been replaced previously so >1 bag of Postfix.

So there’s a big hole – how best to set the new post in … just lots of concrete? Or pack hardcore / slabs in to try and make a smaller fixing area?

Cheers

So there’s a big hole – how best to set the new post in … just lots of concrete? Or pack hardcore / slabs in to try and make a smaller fixing area?

I just shove in old bricks / bits of the old concrete to fill the hole then pour the bag of post crete over / in the rubble.

Did this last week. As above, break up the old post concrete with a lump hammer and chuck half in followed by half a bag of post crete and a litre or so of water. Wait a few minutes then repeat. Fill in with soil an hour later.

Ok, so thinking about the longevity of you new post. You want the base of the post completely sealed in concrete. IE ground water can’t find its way into the wood & rainwater sheds off the concrete that protrudes slightly above the soil level. Using rubble to save concrete is ok as long as the ground water can’t track through the rubble to the wood.

I’d pour some concrete into the base of the hole and allow that to set. Set the post on the dry concrete & pack the rubble round the outside of the hole. Fill the remainder with concrete. Postcrete put in the hole dry will work but generally the top of the dry mix is below ground level. Rain water & ground water will soon find its way into the wood.

Easy job.

I’d get the old concrete out first before working out a solution, had to replace an old fence last year and they’d used a bag of postcrete on one, then two bags (or more) on the next, i broke one up and it left a massive hole, which required work before putting a new post in. My guess would be they did similar to just removing old postcrete, then filling the hole without narrowing it back.

After that though, as above, prep the hole to protect against water ingress, then put post in and add more postcrete, i tend to mix it in a bucket and the pour, just makes a better cement, also making sure to secure post for the 30 minutes or so to set, i.e. that it’s at the right angle and rotation for the fence.

Ok, so thinking about the longevity of you new post. You want the base of the post completely sealed in concrete. IE ground water can’t find its way into the wood & rainwater sheds off the concrete that protrudes slightly above the soil level. Using rubble to save concrete is ok as long as the ground water can’t track through the rubble to the wood.

Can’t say I agree with that.

Having replaced 45 fence posts in concrete – they all rotted at ground level where air could get to the post. The bottom 2′, set in concrete, would often be soaking wet yet solid wood with no signs of rot at all. They all rotted through in a narrow band at ground level.

I kept all the 2′ chunks in concrete, cleaned them up, cut them into 6″ sections and burnt them in the log burner. Decent amount of wood in the end.

Is it just me that struggles to break up the old concrete even with a lump hammer and dulled chisel? I am an office worker so not exactly cut out for squatting in the garden and hammering in a muddy pit!

I stull have a half finished post to fix in the garden.

@toby1
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https://brandonhirestation.com/tool-hire/demolition/concrete-breaker-hire/110v-avt-demolition-breaker

As above, concrete breaker is a hell of a job saver, i wouldn’t even want to think how long breaking up the concrete would have been without one in this type of situation, same with the concrete cutter to cut out large areas of concrete.

In addition to setting posts in concrete I’m using spray bitumen to coat the portion of post in the ground and up to a couple of inches above ground. Possibly not strictly needed but can’t do any harm.

post sleeves are similar to spray bitumen.
Belts and braces!!

@toby1

Is it just me that struggles to break up the old concrete even with a lump hammer and dulled chisel?

Skip the chisel, just use the lump hammer. Mine broke up pretty easily.

Interesting, I was taught not to set wooden posts completely in concrete so it didn’t act like a bucket.

Put gravel in the bottom of your hole, rest your post on that & pour the concrete around that. The wet should then leak out the bottom not rot from the inside out.

Another way of countering the post rotting is by using a concrete repair spur.

I took out the concrete base of one with a sledge and pick and it took forever, back breaking work took a good few hours.

Next time I used a pick to dig around and a long digging bar to get it up and it took about 10 mins to get the lump out whole. Dramatically easier.

Another way of countering the post rotting is by using a concrete repair spur.

That’s the method I use now, everything else is just trying to slow down it rotting.

Another way of countering the post rotting is by using a concrete repair spur.

I’ve installed 45 of them over the last few years…

Repairing Fence Post #1 by Ben Freeman[/url], on Flickr

Repairing Fence Post #5 by Ben Freeman[/url], on Flickr

toby1
Full Member
Is it just me that struggles to break up the old concrete even with a lump hammer and dulled chisel? I am an office worker so not exactly cut out for squatting in the garden and hammering in a muddy pit!

SDS drill & a pointy bit works well.
Our garden used to have a large pond in it. When dismantling it, I spent a day with a lump hammer & cold chisel making some headway. Next day I bought a £100 SDS drill from Screwfix (Bosch) and a set of bits. Made it so much easier. Just get some ear defenders & safety glasses too.

It’s also really useful for jobs around the house where the normal hammer-action drill struggles.