# mixing concrete



## ninjabika (3 Jan 2010)

hi

does any body know how much area a jumbo bag of mixed ballast would cover if mixed with cement to create a concrete base 100 mm thick



martin


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## Jake (3 Jan 2010)

Can't swear to its accuracy but the answers this gives seem about right (4.5 sq metres is the answer it gives to your question).

http://www.practicaldiy.com/general-bui ... -met-2.php


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## ninjabika (3 Jan 2010)

hi

not really sure if that's what i mean. i'll try another way a jumbo bag of ballast is virtually 1mtr cu , so when mixed is it still the same volume i.e from one bag with added cement mixed to a 1-5 ratio could you pour it into a form work 3mtr x 3mtr x 100mm and fill it

any ideas am just running through some costings and ideas in my head


martin


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## Anonymous (3 Jan 2010)

It really depends on how much ballast is in the jumbo bag. When I last had some delivered there was a massive difference between the bags (in terms of quantity of ballast in each). I'm not sure even the biggest was anywhere near 1 cubic metre. I'm pretty sure they were all supposed to be at least 850kg but I'm pretty sure they were all short of this. I fell well short on ballast but was spot on for cement. My guess is that the jumbo bags contain something closer to 600kg.

btw. due to being short of ballast I ended up driving back and forth to B&Q and Wickes most of the day, hence I didn't finish in one day. Next time I'll make sure I've got far too much.

Dave


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## ninjabika (3 Jan 2010)

DustyDave":13b51ih1 said:


> It really depends on how much ballast is in the jumbo bag. When I last had some delivered there was a massive difference between the bags (in terms of quantity of ballast in each). I'm not sure even the biggest was anywhere near 1 cubic metre. I'm pretty sure they were all supposed to be at least 850kg but I'm pretty sure they were all short of this. I fell well short on ballast but was spot on for cement. My guess is that the jumbo bags contain something closer to 600kg.
> 
> btw. due to being short of ballast I ended up driving back and forth to B&Q and Wickes most of the day, hence I didn't finish in one day. Next time I'll make sure I've got far too much.
> 
> Dave




dave

lets just say it did contain a cube of ballast, when mixed would it fill the form work as mentioned ???

martin


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## DeanN (3 Jan 2010)

There are some useful calculators here : http://www.pavingexpert.com/calcall.htm


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## ninjabika (3 Jan 2010)

hi

it's ok, i've found a calculator that gives you what you need to produce a cube of concrete

http://www.builditshop.co.uk/concrete_b ... ac=EGBV2-K

martin


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## Mr Ed (3 Jan 2010)

ninjabika":39sraw2w said:


> hi
> 
> not really sure if that's what i mean. i'll try another way a jumbo bag of ballast is virtually 1mtr cu ,



No its not, it will be a ton. A cube of concrete will weigh around 2.2 tons, so I suspect you will get about half a cube of concrete off a bulk bag.

Ed


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## ninjabika (3 Jan 2010)

Mr Ed":1hwtsu3n said:


> ninjabika":1hwtsu3n said:
> 
> 
> > hi
> ...



cheers , so if i'm right a framework of 3.048 x 3.048 x 100mm (10ft sq 100 mm dp) approx a cube will require 2 jumbo bags + cement + water


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## MickCheese (3 Jan 2010)

I always thought that one cubic metre of water weighs one tonne.

Therefore one cubic metre of concrete will not be too far off one tonne in weight.

I realise there is no real comparison as one cubic metre of polystyrene will be very much lighter and it all comes down to density in the end.

Am I wrong?

Mick


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## WellsWood (3 Jan 2010)

MickCheese":j28ghd2e said:


> I always thought that one cubic metre of water weighs one tonne.
> 
> Therefore one cubic metre of concrete will not be too far off one tonne in weight.
> 
> ...



Last time I checked stones and sand didn't float, so It seems likely they're both a bit heavier than water :wink: 

sorry, couldn't resist


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## Mattty (3 Jan 2010)

MickCheese":26j8iph0 said:


> I always thought that one cubic metre of water weighs one tonne.
> 
> Therefore one cubic metre of concrete will not be too far off one tonne in weight.
> 
> ...


Yes
http://www.readymixdirect.com/questions.asp


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## Mr Ed (3 Jan 2010)

MickCheese":1rzir064 said:


> it all comes down to density in the end.



You've answered your own question there I think, density is the nub of the matter and as said by others, sand and stone are widely accepted to be denser than water.

Ed


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## Benchwayze (3 Jan 2010)

WellsWood":2b09okes said:


> MickCheese":2b09okes said:
> 
> 
> > I always thought that one cubic metre of water weighs one tonne.
> ...



Sorry Mark, but no. 

They aren't 'heavier'. 
Measure for measure they are more dense. Ergo, they sink in water. They could well float in a denser liquid. 

John 

:wink:


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## jasonB (3 Jan 2010)

Ok back to my Quantity surveying days

There are approx 1.6 tonnes of aggregate to a cubic meter depending on exact size of fines and coarse aggregate.

The cement will fill the air voids between the aggregate so adds nothing to the volume, same with the water as this wil evaporate.

Round my way a bulk bag contains one tonne of balast so will yeild 0.625cu mtr of concrete. So at 100mm thick this will cover 6.25 square meters. As you require 9.3m2 you will need two bags and have approx half a bag left over.

Jason


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## MickCheese (3 Jan 2010)

I suppose I asked for that but at least I've learnt two things.

1. Concrete is more than two time heavier than water by volume.

2. Don't post stupid replies to threads.

Mick


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## MikeG. (3 Jan 2010)

One tonne bags don't hold one tonne! Check with your Builder's Merchant, but mine always correct me when I ask for a one tonne bag of anything. I can't remember how much they hold (sorry!), but do know that it is short of a tonne by quite a margin.

Mike


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## Mattty (3 Jan 2010)

One ton bags actually contain 850kg- quite a difference!


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## Dusty (3 Jan 2010)

HI , new to the site .

You find that they are called "bulk "bags , normaly between 800 and 850 kg . And two will just about give you 1metre cube . And even if you are doing 9.5 metres square @100mm thick I would be surprised if you have much more than a wheel barrow left in the bag .

And also you should see how much is in the bag written on a tab ( law) for "lifting " purposes . But you must remember that it was weighed in the quarry/yard . Which tends to be alot wetter at the time so when it reaches you it will weigh less . 

They say the reason they dont weigh a ton is due to health and safety of lifting a ton by lorry . .....but they can lift a pack of concrete blocks at 1.5 ton . It,s a scam . I pay £30 for a bulk bag (800kg) of anything but if I pick it up loose I wouldnt pay above £20 for anything and that will be a whole ton . 

Good luck .


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## WellsWood (4 Jan 2010)

Maybe I've missed something here (it wouldn't be the first time), but regardless of how much ballast is in a "1 ton" bag mixing a cubic metre of concrete seems like an awful lot of work, even with a mechanical mixer (God forbid you would be thinking of mixing by hand :shock. Is there a particular reason you don't want to simply order in some ready-mix?


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## The Bear (4 Jan 2010)

A bulk bag of balast (that you are refering to as a ton bag) contains 0.6 m3 of the stuff. You need 4 bags of cement per bulk bag.

Mark


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## Benchwayze (4 Jan 2010)

I have mixed concrete with a hired mixer in the past. First time I did it, I didn't know much about cement and sand etc. So I went to a builders' Merchant, told them what I was doing, and gave them the dimensions.

The guy behind the counter consulted a chart, and told me exactly what I needed and how much to order. I ordered it, and then went home to await delivery. Easy-peezy! 

These days I have a pal who was in the 'Readimix' org. Apparently the subject of concrete fascinates him still, and he seems to have the answers if it's anything to do with concrete. Next time I see him.... :wink: 

Regards 

John


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## Dibs-h (4 Jan 2010)

WellsWood":2spcdeg9 said:


> Maybe I've missed something here (it wouldn't be the first time), but regardless of how much ballast is in a "1 ton" bag mixing a cubic metre of concrete seems like an awful lot of work, even with a mechanical mixer (God forbid you would be thinking of mixing by hand :shock. Is there a particular reason you don't want to simply order in some ready-mix?



I'd 2nd that - having mixed up the odd M3 of concrete, I would heartily recommend not doing it by hand\mixer. I'd either use ReadyMix or one of the barrow outfits.

By the way - even a petrol\electric mixer will only mix about 70-80L, so that's a lot of mixes.

Although I suppose if you already have a mixer and a spare Sat or Sun - then what the hell - give it a go.


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## JMcK (4 Jan 2010)

Dibs-h":7qeipc66 said:


> By the way - even a petrol\electric mixer will only mix about 70-80L, so that's a lot of mixes.



I have a fairly small electric one which mixes 130L. 

For bigger jobs I use one on the back of the tractor. :wink:


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## ninjabika (4 Jan 2010)

WellsWood":30buwn7s said:


> Maybe I've missed something here (it wouldn't be the first time), but regardless of how much ballast is in a "1 ton" bag mixing a cubic metre of concrete seems like an awful lot of work, even with a mechanical mixer (God forbid you would be thinking of mixing by hand :shock. Is there a particular reason you don't want to simply order in some ready-mix?



HI

no particular reasom why i was looking into quantaties, will probobly go the ready mix route anyway , i just like to weigh up all my options.


martin


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