Waterproofing is the next step of the process, and probably the step I am least confident about because it really is subject to the weather.
We are using a waterproofing membrane called Dual Seal, which has a layer of Bentonite on it. Bentonite is a mineral that swells up on contact with water, so if anything leaks through, the membrane will effectively self-seal. We are laying that face down, so if water comes through the polystyrene, it will catch it on the underside.
Because of how Dual Seal works, we have had to engineer a special steel mesh cage to allow for any swelling of the membrane below. Underfloor heating and the polished concrete floor will then go on top of all this. Getting it right is crucial.
I will be really happy when the floor slab is cast and polished — we can breathe a sigh of relief when I will feel like we have got the unknowns (things so dependent on the weather) out of the way.