Concrete query

[chris123huntin]

Hi All,
I'm planning on concreting an existing shed base. It's 4.5m square and I've recently re-clad & roofed it. The base is bare earth but has always been dry and it's rock-hard. The wooden frame is built on concrete foundations and two courses of blocks. My plan is to concrete up to the top of the first course (roughly 2" above ground level) but I can't work out how to level/finish/float it properly (ie as it's inside I can't use a tamper between formwork)

The other question is whether I need a sub base as the sub grade is so hard - could I get away with a dpm and concrete straight on top? If yes - how thick should the concrete be? If not, how thick should each layer be - for light loading use?

your help's appreciated...

[dig dug dan]

Right, firstly, i would put down min of 3 inches, depending on what you are storing in the shed, ideally 4.
The best way is to screw a batten along two sides at the level you want the concrete, cut a screed rail to the width of the shed, and screed on top of this. Its only a shed floor, so you can leave the battens in place when the concrete has been laid.
If you dont want to leave the battens in place, you will need to fix the batten in some way so it can be lifted out, and then filled in afterwards. Thats a bit more tricky.
I would use dpm, and again a subbase should be put down and wacked, but you could get away with pouring it on the soil. If you were parking a car on it, its another matter

[chris123huntin]

That makes sense and have worked out how to remove the batten.
If I went with 3" of concrete and a dpm, how thick a sub base should I use? I can get planings free - would that suffice given the low loading or is it worth paying the extra for hardcore/MOT1?
PS . i don't want to skimp on the job - want it to outlast me, but I don't want to kill myself or my budget if I don't need to!
PS thanks for the help thus far...

[seanandruby]

don't forget the visquinn. I would use a t tamp, as it's only for a base, or a spazzle/lute.

[chris123huntin]

no, won't forget the dpm...what's the verdict on planings v's MOT?

[dig dug dan]

planings is a swear word on hear unless its for a farm track.
Under no circumstances should the be used as a subbase.
crushed concrete would be best, but it should be good quality. Failing that, MOT.
As for depth, i always put 3" under a shed base.

[GB_Groundworks]

if its good firm strata, then a subbase isn't always necessary, 3 inches of rmc c25-c35 will be fine for the loading imposed in a shed, remove and sharp stones etc or blind with sand,lay dpm then concrete, i.d screw your screed rails on then cut a notched screed rail to sit level with the bottom of the rails. tamp and screed and you can lighlty polish with a float on your way out with wellies on, but if its to wet a mix you'll struggle not to leave trowl marks.

[chris123huntin]

Many thanks for the advice - think I'll go for the sub base option just to be on the safe side. Thanks for all your help - anyone fancy some shovelling next weekend??