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newbie alert

Pier footings concrete ratio

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Hi all, I'm going to start digging for my pier pretty soon...I've been advised to future proof as 1cubic m. I'm setting a 150mm water pipe into this footing and also been advised on a 4-1 mix.. the soil is mainly clay but there was a tree close by which was taken away about 17 years ago so I'm expecting to hit a few roots..

Any advice?

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A cubic meter is probably overkill, my soil is clay and I only did a less than 2 foot square hole.

Five to one is generally a good enough mix,

Dave

Edited by Davey-T

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3 minutes ago, Davey-T said:

A cubic meter is probably overkill, whereabouts in Kent are you the ground can vary from sand to clay to ragstone.

Five to one is generally a good enough mix,

Dave

What you you suggest as a volume?

I'd rather over do than under, as it be too late to add more

Edited by newbie alert
Added info

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1 minute ago, newbie alert said:

Im in Ashford, which is mainly clay..

Yes sorry edited my post now.

Dave

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I'd use a C20 mix.  I bag cement to 2 of sand and 4 of aggregate.  For 1 cubic metre, you'd need 320kg cement, 640 kg sand and 1280kg of aggregate (10-20mm).  Oh and about 300 litres of water.  For that quantity it's worth considering a readimix delivery.

I've never been impressed by the 1m3 isolated cube for a pier foundation argument.  When I eventually get round to building my own, I'll just pour a 150mm thick slab for the whoe thing and build a pier from concrete blocks on top of it.  :)

ETA

Oh and I'm on glacial till i.e clay with rocks in it.

Edited by Islander
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A 5-1 mix is all that’s needed, 5 parts ballast and 1 cement, I did mine at the end of the summer last year, 600mm square block, then drilled 18mm holes for resin studs three weeks later after it was set enough to drill, but not so rock hard it would crack when drilling... 👍

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24 minutes ago, Islander said:

I'd use a C20 mix.  I bag cement to 2 of sand and 4 of aggregate.  For 1 cubic metre, you'd need 320kg cement, 640 kg sand and 1280kg of aggregate (10-20mm).  Oh and about 300 litres of water.  For that quantity it's worth considering a readimix delivery.

 

ETA

Oh and I'm on glacial till i.e clay with rocks in it.

Thanks for the advice,  I've already got the sharpsand, just need to get the aggregate.. which again is another thing to dither over, 10 or 20mm ? 

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16 minutes ago, WanderingEye said:

A 5-1 mix is all that’s needed, 5 parts ballast and 1 cement, I did mine at the end of the summer last year, 600mm square block, then drilled 18mm holes for resin studs three weeks later after it was set enough to drill, but not so rock hard it would crack when drilling... 👍

I did contemplate on doing the re- bar method but as I already have the pipe i just use that

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12 minutes ago, newbie alert said:

10 or 20mm ? 

20mm, if your intent on that much cement you'll need to hire / buy a mixer.

Dave

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My block was something like 600mm cube or a bit less with integral pier, poured in one go (took all day) and it's solid as a rock - oh - it is a rock, effectively!!

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8 hours ago, Davey-T said:

20mm, if your intent on that much cement you'll need to hire / buy a mixer.

Dave

Don't worry Dave, I already have one..

It's the digging I'm worried about!

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I put down 1 cubic metre for a rig weighing in at around 180 kg.  It did look like a very deep hole but my thinking was I have one shot at this and I did not want it coming up short.

D783BE76-CDCD-4808-8294-B15903EF73B2.jpeg

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11 hours ago, newbie alert said:

I did contemplate on doing the re- bar method but as I already have the pipe i just use that

I wouldn’t worry about rebar, I actually mixed mine is a large builders bucket with a plasterers electric mixing paddle, took 24 bucket loads, 1 bucket load was 1  5-1 mix, and took just 2.5 hours..

the paddle was a godsend and created a great mix...

here is my story..

 

Edited by WanderingEye

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My advice is to run pipe in to take cabling before you pour concrete  even if it’s just for future proofing , I  used 2” pipe but should have use bigger pipe something like 3” gutter pipe .

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2 hours ago, WanderingEye said:

I wouldn’t worry about rebar, I actually mixed mine is a large builders bucket with a plasterers electric mixing paddle, took 24 bucket loads, 1 bucket load was 1  5-1 mix, and took just 2.5 hours..

the paddle was a godsend and created a great mix...

here is my story..

 

Thanks for the write up, interesting read

I have a cement mixer to do the mixing for me so my drill and paddle can take a day off..

Thanks again 

Edit...22 bucket full and 2.5 hours..

That's a bucket every 7 mins...

Need some of what you're on..

Edited by newbie alert
Added info

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1 hour ago, newbie alert said:

Thanks for the write up, interesting read

I have a cement mixer to do the mixing for me so my drill and paddle can take a day off..

Thanks again 

Edit...22 bucket full and 2.5 hours..

That's a bucket every 7 mins...

Need some of what you're on..

Lol, may have been closer to 3 hours, but it was six shovels in a bucket add water and mix, pout in hole, so not much more than 7 mins per bucket, probably only 3-4 with the mixing paddle...it made really easy work of it,  better than a mixer really, certainly quicker...  👍

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23 hours ago, newbie alert said:

Thanks for the advice,  I've already got the sharpsand, just need to get the aggregate.. which again is another thing to dither over, 10 or 20mm ? 

14mm?  :D

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On 14/01/2020 at 09:00, tomato said:

I put down 1 cubic metre for a rig weighing in at around 180 kg.  It did look like a very deep hole but my thinking was I have one shot at this and I did not want it coming up short.

D783BE76-CDCD-4808-8294-B15903EF73B2.jpeg

Do you see where the soil changes colour? Thats the depth you actually needed to go down to. 

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In general there is no point in digging deeper than the local water table either. The biggest point with this is not stability during imaging (you will get that with a tripod on a patio), its that you want to set your polar alignment and not have it change over time as the pier settles or the water table rises and falls. 

Adam

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2 hours ago, Adam J said:

In general there is no point in digging deeper than the local water table either. The biggest point with this is not stability during imaging (you will get that with a tripod on a patio), its that you want to set your polar alignment and not have it change over time as the pier settles or the water table rises and falls. 

Adam

Interesting. Hadn't considered that on my build - haven't dug it yet so time yet to ponder! Was planning for a 800x800x1000 cube but my site is about 10 metres and probably less than a metre in elevation from a drainage ditch - it's what I've got to work with. Wonder if a more shallow but wider base might be more sensible.

The 1 cubic metre volume I think is about right - probably slightly excessive but definitely enough to resist any forces on the pier. It's also the smallest volume any premix truck will do you, so 🙂

Would definitely aim for C20 or better spec-wise, either way, ideally C30.

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Just now, discardedastro said:

Interesting. Hadn't considered that on my build - haven't dug it yet so time yet to ponder! Was planning for a 800x800x1000 cube but my site is about 10 metres and probably less than a metre in elevation from a drainage ditch - it's what I've got to work with. Wonder if a more shallow but wider base might be more sensible.

The 1 cubic metre volume I think is about right - probably slightly excessive but definitely enough to resist any forces on the pier. It's also the smallest volume any premix truck will do you, so 🙂

Would definitely aim for C20 or better spec-wise, either way, ideally C30.

A cubic metre is far far to excessive, and just not needed, my hole was 600mm cubed, and that was more than enough, the weight of that block fixed in the ground is huge... 😀👍

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I didn’t hit the water table, for sure 1 cubic metre is too much, but how close to the wind do you want to sail? A tripod gets its stability from its geometry, a pier gets its stability from the mass it is anchored to.

I come back to my original point, it’s a job I only wanted to do once, imaging rigs tend to get heavier over time and you cannot easily add concrete to your original construction.

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18 minutes ago, tomato said:

I didn’t hit the water table, for sure 1 cubic metre is too much, but how close to the wind do you want to sail? A tripod gets its stability from its geometry, a pier gets its stability from the mass it is anchored to.

I come back to my original point, it’s a job I only wanted to do once, imaging rigs tend to get heavier over time and you cannot easily add concrete to your original construction.

True, rigs get heavier, but not to that extent, the size of concrete you are talking about (1 cubic metre) would hold a ship in port....you would need somewhere in the region of ten tons of force to even move that block a mm.... 😀

 

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