Laying a concrete base?

So I understand the basics (although a run through would be good) but how do I work out how much concrete I need? I'd prefer to use premixed bags purely for ease...

it's an 8x6ft greenhouse

 

I think we need more info, like how thick you intend, or if you will be completely covering the area or just making a base for it to stand on.
My greenhouses are on a raised 4 in wide concrete surround.
The actual area of the greenhouse is slabs and shingle laid on a membrane.

 

I intend to completely cover the entire area and thickness is really whatever it needs to be...

 

I would think twice about complete coverage as this once laid instantly sets/reduces growing height and growing options. A lot of people complain about the restrictions of a complete base.
regards Alex

 

I will have a complete monoculture of cacti so this won't be an issue, but thanks anyway.

Sent on the go from my telephone

 

Hi Icecoldrum. Ive just completely redone my garden including doing my own giant concrete floor in the shape of a flower. I really couldn't say how much stuff you need (I got tonne bags in and cant remember how my I got in the end) but I would suggest that unless money isn't an issue then you take the extra time to mix your own, premixis going to be a huge cost compared to getting the cement, sand and ballast separate. And remember to put a layer of stones down for your concrete to go onto. Good luck with it. Its hard work, but so worth it.

 

16 cubic feet = 4ins deep

 

Okay so Bumballina is on the money premix is way too expensive! so please bear with me DIY is really not my strong point!

I found this video which looks pretty straight forward



I've looked at calculators online and they are very confusing... what sort of mix should I be using for a slab? I've found that B&Q sell bags of ballast for £1.50ish if you buy 10+ (ballast is a mix of gravel and sand?) and then I can just add cement and water? I can rent a cement mixer for just £20 a week locally so that makes it a bit easier on my back.

and I see they also sell timber which I could use to make up a frame

http://www.diy.com/departments/softwood-sawn-timber-t47mm-w100mm-l2400mm/555343_BQ.prd

so that would make the base just shy of 4"

so based on say my current greenhouse which is 8x6ft (exact base dimensions are 1920mm x 2542mm) how much extra either side should I leave?

 

I think I'm just going to do concrete footings and then add a single row of concrete blocks on there side for height... that's something I feel might be able to achieve...

 

I would go for the footing way and solid concrete blocks. You could put some 300 x 300 slabs for a path and grow into the soil or in containers on top. More alternatives this way concrete is very permanent.