Concrete Posts

karlitob · 25-06-2020 5:56pm #1

Hi all

I’m installing concrete h posts and wooden fences over 150ft.

Post Length:
I’m getting caught up in knots as to the length and depth required. I want 2.1m above ground (1.8m fence and .3m gravel board) but I’ll stuck on whether to get a 2.7m or 3m. I know that 2.7m is the norm with .6m underground, but I wondered would it be better to go with the .9m so that it’ll be more secure. I’m worried that the length of the run needs a deeper hole. I think I read that it’s not the concrete that gives the post it’s strength against lateral movement but rather the depth. I have a petrol auger and no problem hitting the .9m

Concrete
I know that the recommended is 1:6 cement:ballast but again, for belt and braces I read that I should go to 1:4.

Any comments appreciated. I don’t just want to do it, I want to do it right and make sure it’s lasts a long time.

BryanF · 25-06-2020 9:22pm

What’s the ground like? Plenty of big stones packed in with concrete and the 2.7m posts would be the norm. Have you help? You need two at least.

karlitob · 25-06-2020 10:09pm

BryanF wrote: »

What’s the ground like? Plenty of big stones packed in with concrete and the 2.7m posts would be the norm. Have you help? You need two at least.

I’ve a hand when I need it. I can get them in position and I’ll have someone to hold it for me.

So stick with the 2.7?

Calahonda52 · 26-06-2020 10:07am

I thoght this job was finished:D:D

It depends to a certain degree on how big the auger hole is.
Its the surface are of concrete that provided the resistance so if the hole is narrow WRT the width of the post then you need deeper.
Think about a canoe paddle vertical in the water vs an oar
Re the concrete, 1:6 [1 cement to 6 of gravel or sand plus aggregate ] is even overkill once it sets.
1:4 is a waste, it will set quicker, maybe even in the barrow

When I was growing up in the 60's and cement was v expensive and money was scarce, my father mixed it out at 24 to 1 for 1" floors for foot traffic: they are still there, needed priming for dust suppression but nothing else

Concrete cures pretty much in 7 days, 70% of strength, and then reaches max at 28
It sets after about 24-48 hours

I think I mentioned it already , a small electric concrete vibration poker and proper additive will make getting the concrete really snug so much easier, especially if a narrow 900mm deep with the post in place.

karlitob · 26-06-2020 1:20pm

Calahonda52 wrote: »

I thoght this job was finished:D:D

It depends to a certain degree on how big the auger hole is.
Its the surface are of concrete that provided the resistance so if the hole is narrow WRT the width of the post then you need deeper.
Think about a canoe paddle vertical in the water vs an oar
Re the concrete, 1:6 [1 cement to 6 of gravel or sand plus aggregate ] is even overkill once it sets.
1:4 is a waste, it will set quicker, maybe even in the barrow

When I was growing up in the 60's and cement was v expensive and money was scarce, my father mixed it out at 24 to 1 for 1" floors for foot traffic: they are still there, needed priming for dust suppression but nothing else

Concrete cures pretty much in 7 days, 70% of strength, and then reaches max at 28
It sets after about 24-48 hours

I think I mentioned it already , a small electric concrete vibration poker and proper additive will make getting the concrete really snug so much easier, especially if a narrow 900mm deep with the post in place.

Ha. Still on the clearance so loads of time to think!!

I’ve read, and advised, that the hole should be three times the width of the post. So I’ve a 300mm auger bit ready.

BryanF · 26-06-2020 9:03pm

A poker! For posts? Calahonda you’re having a laugh!

karlitob · 30-07-2020 7:28pm

One more question!

How far up do you fill the hole with concrete.

I’ve my 900mm depth dug - fence in. All plumb and looking good. But by first batch - wheelbarrow full is only coming about half way or more up. Should I go somewhat close to the top or does it matter.

Thanks on advance.

Calahonda52 · 30-07-2020 8:53pm

BryanF wrote: »

A poker! For posts? Calahonda you’re having a laugh!

Absolutely not.
I have been working with concrete since 1963 and the two big breakthroughs for me were my first 1/2 bag concrete mixer and my first small concrete poker, a god send when working alone

Calahonda52 · 30-07-2020 8:54pm

karlitob wrote: »

One more question!

How far up do you fill the hole with concrete.

I’ve my 900mm depth dug - fence in. All plumb and looking good. But by first batch - wheelbarrow full is only coming about half way or more up. Should I go somewhat close to the top or does it matter.

Thanks on advance.

It does matter you should come up to about 100 shy of ground level and cover with top soil

karlitob · 30-07-2020 11:38pm

Calahonda52 wrote: »

It does matter you should come up to about 100 shy of ground level and cover with top soil

Thanks - I’ve one done. Is it ok to put new mix onto the day old mix?

rampantbunny · 31-07-2020 10:58am

Some things to consider OP.
In the past we would have filled the concrete around the post to the underside of where the boards were going to be. Gives something solid to rest/support the boards on between posts. Even if using timber boards, this helps but less important as less weight to support. I've seen rushed jobs where concrete gravel boards sank between posts due to lack of support. Soil can expand contract and all that.

Top soil above the concrete means grass/other can grow, but you might want not want growth at the bottom of the posts...difficult to mow. Same at base of gravel boards, you might want to keep growth a few inches away from the fence.

karlitob · 03-08-2020 7:20pm

rampantbunny wrote: »

Some things to consider OP.
In the past we would have filled the concrete around the post to the underside of where the boards were going to be. Gives something solid to rest/support the boards on between posts. Even if using timber boards, this helps but less important as less weight to support. I've seen rushed jobs where concrete gravel boards sank between posts due to lack of support. Soil can expand contract and all that.

Top soil above the concrete means grass/other can grow, but you might want not want growth at the bottom of the posts...difficult to mow. Same at base of gravel boards, you might want to keep growth a few inches away from the fence.

Thanks for that. I don’t really want to have grass right up to it. A nice border would really suit me.

On advice, I have bricks supporting either end. Will concrete them in when all finished. Any advice on filling in that gap. I’ve soil that I dug out of each hole which I could use but wondered if there was another method.

Thanks.

karlitob · 03-08-2020 7:21pm

karlitob wrote: »

Thanks for that. I don’t really want to have grass right up to it. A nice border would really suit me.

On advice, I have bricks supporting either end. Will concrete them in when all finished. Any advice on filling in that gap. I’ve soil that I dug out of each hole which I could use but wondered if there was another method.

Thanks.

Forgot pic.

karlitob · 05-08-2020 9:30am

karlitob wrote: »

Forgot pic.

Appreciate any advice on how to finish underneath gravel board. Thanks all.

rampantbunny · 10-08-2020 2:01pm

karlitob wrote: »

Appreciate any advice on how to finish underneath gravel board. Thanks all.

Was away, only seeing your question now.
If it were my own job I'd pour concrete underneath, but I've a mixer here and aggregate so this is the easy option for me. If I didn't have these, I'd just backfill with soil and resign myself to keeping the growth in check using a strimmers.

karlitob · 10-08-2020 7:08pm

rampantbunny wrote: »

Was away, only seeing your question now.
If it were my own job I'd pour concrete underneath, but I've a mixer here and aggregate so this is the easy option for me. If I didn't have these, I'd just backfill with soil and resign myself to keeping the growth in check using a strimmers.

Thanks for getting back to me.

There is NO way that I want to be clearing growth - either from my side or the battle axe next door.

So I’m all ears about the concrete. How far down would I go? I’d need a thick amount if it were to keep its shape. How would you stop spilling into other side - small bit of mesh?

I was thinking of putting in some form of peddle edge. Dig down 200mm - fill with stone, compact, spread with pebble on top.

Calahonda52 · 10-08-2020 8:47pm

any chance of a photo along the fence for perspective

karlitob · 10-08-2020 11:53pm

Calahonda52 wrote: »

any chance of a photo along the fence for perspective

Here you go

chooseusername · 11-08-2020 12:02am

karlitob wrote: »

Here you go

Knock out the support bricks and drop them all down the 4 or 6 ins

karlitob · 11-08-2020 8:07am

chooseusername wrote: »

Knock out the support bricks and drop them all down the 4 or 6 ins

No thanks. Sure they’re at that height on purpose. Besides - the ground changes all the way along.

rampantbunny · 11-08-2020 8:52am

chooseusername wrote: »

Knock out the support bricks and drop them all down the 4 or 6 ins

Presuming the OP has the top of the fence panels flush with top of posts, then this wouldn't look right.

OP, I've two assumptions given the the picture you posted. Firstly, you want your lawn to finish closer to the fence, but also, it looks like the underside of your concrete boards are higher than the lawn.
I haven't installed a lawn mowing strip/edge myself but I've been told it should be marginally above the level of the soil in the lawn (allowing lawnmower wheel to travel along). Easiest thing for you could be to dig along a straight line in front of your fence and install some treated 2 x 4 on edge. You have options then for back-filling. Concrete from the top of the board, sloping up to the underside of the concrete plinths. Depending on slope, you might want to come away from the fence a bit so the slope is not so aggressive. Coming away from the fence a bit also allows you to throw a few flower-boxes/planters in front of the fence later if wanted.
If you don't like concrete look, concrete with decorative stone on top. Or, forget the concrete, throw in your left-over soil, weed-barrier on top, and decorative stone on top of that. With decorative stone on top I'd still anticipate that over the years you will get some weed growth - that's nature.
It's all subjective...hard to determine what you are looking for, how much effort you want to go to, expense etc.

PS. if you are considering a lawnmower edge strip, think about curving the strip as you meet whatever walls/fences are perpindicular to your new fence. Curves are easier mow around than corners.

karlitob · 11-08-2020 9:23am

rampantbunny wrote: »

Presuming the OP has the top of the fence panels flush with top of posts, then this wouldn't look right.

Correct. They base of board is at ground level near house but it rises and changes a lot over the course of the garden -150ft long

Calahonda52 · 11-08-2020 9:24am

very neat job, you would get the start any day!

Have you access to the other side?

rampantbunny · 11-08-2020 9:31am

karlitob wrote: »

Correct. They base of board is at ground level near house but it rises and changes a lot over the course of the garden -150ft long

150ft long...I didn't get that from your earlier pic. I wouldn't be mixing concrete for this length. Bark mulch could be a nice option. I'd still install a lawnmover strip.

chooseusername · 11-08-2020 9:57am

karlitob wrote: »

Correct. They base of board is at ground level near house but it rises and changes a lot over the course of the garden -150ft long

In fairness it looked fairly level to me ,
but I realise we can only see quarter of the panels.
Some job getting post-tops and 25 panels level over uneven ground.
I'd have taken the easy route and stepped the levels or depending on
the difference in levels ,buried the gravel boards in the high parts.

karlitob · 11-08-2020 11:36am

Calahonda52 wrote: »

very neat job, you would get the start any day!

Have you access to the other side?

Thank you. I’m delighted with myself. Had lots of help and advice (including your good self).

I do-ish. She’s a pain the hoop but if I needed I might. Just depends on what. But I’d rather not. What did you have in mind.

Calahonda52 · 11-08-2020 12:02pm

Am trying to figure out how to get the gravel boards supported by concrete to allow you take out the bricks/fill the gap underneath and at the same time not make a mess of what is straight out of a catalogue!

Day job is getting in the way.

Have you access to a 2 or 3 ton bottle jack to allow you take the weight of the boards to remove the bricks and insert something else..
.
Have not figured it out yet

rampantbunny · 11-08-2020 2:19pm

Calahonda52 wrote: »

Am trying to figure out how to get the gravel boards supported by concrete to allow you take out the bricks/fill the gap underneath and at the same time not make a mess of what is straight out of a catalogue!

Day job is getting in the way.

Have you access to a 2 or 3 ton bottle jack to allow you take the weight of the boards to remove the bricks and insert something else..
.
Have not figured it out yet

Mark the post, raise each gravel board a few inches, drill through post and pop in a bit of rebar (or bolt or whatever else you have to use as a strong peg). Let board rest on rebar each side.
I'd keep boards up until concrete is set. Keep them clean plus no need to have them stuck or bedded in.

But that's 150ft of concrete ..overkill?

karlitob · 11-08-2020 3:33pm

rampantbunny wrote: »

Mark the post, raise each gravel board a few inches, drill through post and pop in a bit of rebar (or bolt or whatever else you have to use as a strong peg). Let board rest on rebar each side.
I'd keep boards up until concrete is set. Keep them clean plus no need to have them stuck or bedded in.

But that's 150ft of concrete ..overkill?

Thanks for that. I’m getting a little confused.

At each post hole, there is a lot of concrete. I have brick and block with some slate to pack at correct height at most of the posts. I plan on packing either side of each post with brick block and slate to ensure that each board is at the right level and that there is no brick on the ground/muck. I think this is the correct approach to ensure a level finish that won’t move (ground movement with frost etc) but what I don’t know is whether I should concrete or mortar those bricks and slate that will be against the post so that it won’t move in the future. I’m worried about concrete on top of concrete and whether it might split in future.

Do you (Or others) mean to put the concrete along the 1.8 metre of the bottom of the gravel board?

Thanks for all advice.

rampantbunny · 11-08-2020 4:23pm

karlitob wrote: »

Thanks for that. I’m getting a little confused.

At each post hole, there is a lot of concrete. I have brick and block with some slate to pack at correct height at most of the posts. I plan on packing either side of each post with brick block and slate to ensure that each board is at the right level and that there is no brick on the ground/muck. I think this is the correct approach to ensure a level finish that won’t move (ground movement with frost etc) but what I don’t know is whether I should concrete or mortar those bricks and slate that will be against the post so that it won’t move in the future. I’m worried about concrete on top of concrete and whether it might split in future.

Do you (Or others) mean to put the concrete along the 1.8 metre of the bottom of the gravel board?
Thanks for all advice.

That is what I meant i.e. concrete along/under the bottom of the board. Extend concrete out a little from the fence so that it is easier to mow. I initially mentioned concrete because less maintenance with weeds, plus support under your boards. But that was before I knew the length of your fence.
Now I reckon it is overkill. If you think your existing props won't sink or move backfill the voids with your soil, weedbarrier and then bark mulch (remembering to install the lawnmower strip for a good straight line). This will give a nice border plus you don't have as much soil to dispose of if any. No concrete means you can plant flowers/shrubs there in the future. See left of this picture: https://images.app.goo.gl/ixFstDqqKNB48tTE9..soil area available beside lawn..potential to look really good.
If you think your props will sink or move get some 4" blocks, cut in two and bed in concrete under each end of the boards. Then same as above re. soil and mulch.

Calahonda seems to be more clued in on your situation...I mean, it might be difficult for you to get some 4" blocks but easy to get/mix concrete.

That's all I've got anyhow.

karlitob · 11-08-2020 11:38pm

rampantbunny wrote: »

Presuming the OP has the top of the fence panels flush with top of posts, then this wouldn't look right.

OP, I've two assumptions given the the picture you posted. Firstly, you want your lawn to finish closer to the fence, but also, it looks like the underside of your concrete boards are higher than the lawn.
I haven't installed a lawn mowing strip/edge myself but I've been told it should be marginally above the level of the soil in the lawn (allowing lawnmower wheel to travel along). Easiest thing for you could be to dig along a straight line in front of your fence and install some treated 2 x 4 on edge. You have options then for back-filling. Concrete from the top of the board, sloping up to the underside of the concrete plinths. Depending on slope, you might want to come away from the fence a bit so the slope is not so aggressive. Coming away from the fence a bit also allows you to throw a few flower-boxes/planters in front of the fence later if wanted.
If you don't like concrete look, concrete with decorative stone on top. Or, forget the concrete, throw in your left-over soil, weed-barrier on top, and decorative stone on top of that. With decorative stone on top I'd still anticipate that over the years you will get some weed growth - that's nature.
It's all subjective...hard to determine what you are looking for, how much effort you want to go to, expense etc.

PS. if you are considering a lawnmower edge strip, think about curving the strip as you meet whatever walls/fences are perpindicular to your new fence. Curves are easier mow around than corners.

Thanks for this. Sorry I missed it earlier.

Yes - you’re right. It is higher than the lawn - or “lawn”. It’s not great. The height changes a bit over the run.

One problem is that I don’t know exactly what I want all along the fence - some parts will be the back of a shed, others parts beside lawn, and others raised garden beds etx so I know I need to figure out what I want.

Am I right in saying that your suggesting put down a 2x4 on edge to fill up the space somewhat underneath the board

Or is it to put a 2x4 on edge about 6inches from the fence and have that as your mowing strip. I can then backfill with concrete - or whatever.

I think I’d like to have a finish as in the picture along some part of the fence.

Concrete Posts

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