Concrete how thin?

[Geordie Boy]

Hello,

I am building a shed base for a 6' x 8' shed which I am going to buy to replace a 5' x 8' precast concrete shed which I have just demolished. There is a concrete base left from the old shed, which I am extending by 1' at one side.

Problem is, the existing base has quite a cross-fall to it and I want the base for new shed to be level. I have cast 1' wide of concrete flush with the 'high side' of the existing base and now want to level it off.

Question is, how thinly can I lay 20mm aggregate concrete on top? I am planning to extend the shutter that I have already used on the 'high side' and shutter the 'low side' so it is level without causing s feather edge, but how thin can it be at the high end?.

I know I could do this with paving slabs on a mortar bed but I already have plenty sand, cement and gravel (20mm). Obviously I don't want to mix any more concrete than I need to.

Hope this can be understood, any advice greatly appreciated.

Thanks

[seanandruby]

75ml