Well I have to admit to leaving everyone in suspense about what is happening down there, here is a picture I took last week, now looking at this you can see the sky through the concrete plinths, now these are like 30cms wide, 5cms deep and probably upto 5 meters long, you can order the size you need, anyway these are just laid across the beams and then more rebar/steel-work is chucked on top and then another concrete pour is done, as you can see they are supported with old bits of wood so they don't collapse or sag too much, I have to admit everyone we have tiled though the original floor sags in the middle by about 3 cms have to use loads of cement to correct that