pouring floor in basement

[joachim-i-bohuslän]

Recently became the owner of a holiday home in Bohuslän. Built around 1900, the wooden house is constructed on a solid granite foundation with standing height in the crawl space/basement.
Now the question.
Half of the basement is cast, the rest is an earth floor (a lot of sand and small stones in the soil, but still naturally damp).
I have started digging out, laying drainage, and filling with stone to then cast the other half of the floor. Are there any reasons not to do this? Can it worsen the moisture situation? I'm perplexed as to why the previous owners didn't lay concrete throughout the basement.
I have dug around the chimney in the middle of the space and reached a concrete slab that the chimney seems to stand on, about 25 cm below floor level. Any issues with casting on top of this and around the chimney?

Grateful for any responses.

 

[Steinmeister]

You should make sure to include a capillary-breaking layer, Pordrän/isodrän or washed macadam that you compact. If you cast directly on the existing surface, you'll get a concrete slab that will absorb moisture.

Granite stone doesn't absorb any water, so it's a good foundation; the risk is that water might flow in between the stones.

The floor structure can't handle the weight of a fireplace, so it was built either on a large stone or a concrete foundation. No problem casting around it.

I think your plan sounds good, go for it.

PS close the vents to the foundation now during the summer so that warm humid air doesn’t get in.