Hi all I wonder if you can help, I’m pretty new to all this. I’m gonna build a concrete base for a shed, 8ft long 5ft wide and 10cm depth. Roughly 0.37 m3. (Please note that the 10cm depth does not include the mot 1 sub-base). Anyway How many bags of cement to mix ballast will I need? Any help is greatly appreciated!!
You should get away with 1 bulk bag BUT they do come in different sizes so bear this in mind you probably want about 800 kg, 6 bags of cement. 6:1 will be fine but keep the mix nice and stiff: you will get much better concrete as a result. Cover it with polythene when you're done to cure it. Take the time to get your shuttering accurate and solid. Base a tad smaller than the shed to avoid water getting under.
I would go for 1:5 and a 800kg bulk back should do it with 6 of cement (get 7 just in case. Also worth adding a handful of polyester fibres to each mix..
If its just a shed on level ground you might consider Eco base from Wickes and other places. I've done two shed bases with it and it was endorsed by the shed installer. Costs are about the same