One pour concrete hearth

[lamby]

Hi All,

I've got my blocks 4 courses high so I'll be shuttering for my hearth soon.
I'm thinking I can create my hearth for my oven which will act as my build platform for the dome as one pour. 

I'll do this with a couple of 900x600 concrete slabs I've got spare in the garden. Two slabs will be supported on 3 concrete lintels, lintels supported on my block work. Onto these I'll put either 50 or 75mm cal-sil boards and then my 64mm Fire bricks. A video on YouTube show the firebricks surrounded by a bit of insulating wool (for expansion) but I think this will also act as a good heat break between the hearth and the slab. (I don't want to be heating the entire concrete slab! I then plan to shutter this off and do a single pour 115 or 140 depending on insulation thickness, with some rebar in the centre for additional strength. A quick calc makes me confident the slabs will support the concrete until set.
 
My hearth slab edge will be on show (probably painted eventually) so I want a nice neat edge and finish. Most builds appear to do 2 pours - I think the use of the slabs make things a little more simplistic - I think.

Any thoughts on the above?

Thanks
Chris

[lamby]

Ah. Maybe this is a no no!
After a little more research, I guess the cal-sil board will absorb the water from the wet concrete!!