# Forum Home Renovation Concreting  Bags of cement per M3

## wannabe

Can anyone tell me how many bags of cement are needed for 1 cubic metre of concrete at a 3:2:1 mix.
If I go to CementAustralia they say 20 bags per metre.
If I go to BlueCircle they say 16 bags per metre. 
Which one do I believe?

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## Terrian

14 for 20mpa concrete
16 for 25mpa concrete
20 would be about 32mpa I think 
what is the concrete going to be used for ?

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## wannabe

Thanks Terrain. It would be helpful if they would state this on their websites.
I'm pouring a slab for a garden shed. Slab is 2.4m x 2.4m x 75mm with plastic underneath and 5mm reo.  Mix will be 3:2:1. I think the 16 bags = 25mpa should be ok for this.

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## autogenous

> I think the 16 bags = 25mpa should be ok for this.

  What soil type do you have? 
Be sure to put black plastic underneath to stop moisture ingress. 
Mix the concrete with a bucket to make sure you are mixing by proportion. buckets ready, go! 
Too much water = weak concrete and cracking.  
It maybe cheaper to order the concrete. Have you checked ? It could be worth it structurally and from a finish perspective. Less chance of cold joints. 
Go the stipple finish.

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## wannabe

Soil type is typical Canberra pug. For anything other than a garden shed I would be going for a thicker slab and bigger steel.
Definitely putting plastic under the slab. 1) it will slow it from going off too quick while I mix and lay the concrete  2) cut down on moisture in the shed
It's only 0.43M<SUP>3 </SUP>so I didn't even consider premixed plus it would have to be barrowed in too. I've got a loan of a cement mixer from the neighbour and calced it's only about 7 mixes to get it done so it's nothing too major. In my younger day I've formed, prepped and poured quite a few house slabs. We also used to dig, steel and pour house footings in a day. They were big days. That was all using premixed and I've never really done any serious concreting mixing it myself but once it's in there I know what I'm doing. I like the idea of using buckets for proportioning rather than shovel loads. I'm not as young as I used to be either. I found out years ago I suffer from an allergic reaction to concreting "I break out in a sweat every time I do it" :Biggrin:

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