How do I lay a level slab?

[iDIY]

Hi Guys,
I have dug a 1m deep, 26m long trench and had 300mm of concrete pored in the bottom. I have built up to just below 'ground level' with 300mm wide trench block. I will be laying another course of 100mm concrete blocks to form an inner and outer leaf to get to at least 150mm above ground level for DPC. At that point I will be pumping in concrete to form the slab on top of the sand and DPM of course.

As the DPC layer will be 150mm above the level of the slab, I can't use the inner leaf to get the concrete level and I can't put timbers either side to get it level. So what is the secret to getting it level?

 

[^woody^]

Options

1. Voodoo
2. Lots of water on the top and a depth gauge
   
3. A levelling board

Note: no wellies required with option (1)

 

[Notch7]

So what is the secret to getting it level?

Well since most builders dont get concrete oversite very level, I would say its a highly guarded secret!

some builders stop at oversite level, then cast, then carry on. to do that may mean cutting blocks or using a brick course or 2.

or you could make up some tamp boards from 6 x 2 and screw a bit of 4 x 2 flat on the ends overhanging by a foot or so -that depends on the shape of your oversite -a tamp board like that would work on a smallish extension, or one with various bays. If bigger then the same might work going across the corners

and you could have a laser level on and mark a datum line on a stick and check at various points.

or Voodoo!

You need a good pumping team with radios -Ive had it happen where they pump in too much then once its pushed around its too high, needing some to be shovelled out.