help needed to calculate concrete mix

Bonbon

Can anyone help me calculate how much concrete I need for a shed base 3m x 2m. It's dug out to 6" deep and half filled with hardcore. I have searched the internet and just about everyone/company is telling me different.
What are the options? I know you can mix it yourself or buy cement plus 'all in' ballast, or get bags of readymix concrete and just add water.
I have seen ratio of cement/sand/gravel at 1:3:6
and another site calculated that I need 7x25kgs cement + 1.05 tonnes ballast
I'm totally confused. Me and b/f want to do it over the bank holiday and have booked the cement mixer so now just need to know what to mix.
I'd be grateful for any help thanks.

ormus

6/11/22 x 25kilo bags.
cement/sharp sand/ballast

or get half a cubic metre delivered by ready mix lorry. much easier.

ps
1 2 4 ratio.

Bonbon

Cheers ormus.How do I mix it? eg.ratio into the mixer, sorry but I'm not good at maths.

keystone

Ballast is a mix of sharp sand and gravel. Why would you want sharp and ballast separately?

Yes I'd say a 1 tonne bag of ballast and 7 bags of dust too.

Cheers

Edit - Most readymix companies work on the basis of a minimum delivery of 1m3. I reckon you only need about 0.5 as Ormus says.

DVardysShadow

2 shovels of ballast 1 of sand 1 of cement 1 of sand 2 of ballast into the mixer turn over until evenly mixed add water. Or stop at the cement turn over add water turn over some more add remaining sand and ballast, turn over, add a little water if required.

There are many combinations and if you are experienced you will find yourself changing the order a bit for the best mix according to your materials. It is important not to start with cement and to have the cement well turned in before adding any water.

Bonbon

Job done! Not bad for a first attempt. I'm still wondering how I ended up laying the concrete while b/f stood watching the mixer, in case there was a problem.

vaio

any clown can hump & lay concrete but would you know what to do in the event of a mixer emergency? a lot of complicated technology in a mixer, needs expert watching

sounds like between you you've done a good job