Floor filling - what are your thoughts?

[cpalm]

Currently shoveling out about 20 cm of joist cavity fill in a future bathroom, which of course raises the question of what to replace it with. The fill seems to consist of wood ash, plaster remnants, sand, and various wood scraps carefully topped with a few centimeters of sawdust.

The conditions are as follows:
1) It's an intermediate floor above a heated basement, so besides having hydronic underfloor heating, thermal insulation is not a crucial factor.
2) It's understood that the current material's high density provides excellent acoustic properties. No one is directly sleeping in the basement, but I don't want to lose the feel of a solid and quiet floor.
3) Mice tend to move in the joist cavities today, likely in the sawdust layer, which I'd like to prevent.
4) Fire protection is not really an issue in a bathroom on a concrete floor, but I would like to experiment with fire-safe alternatives for future projects where there are wooden joist floors insulated with sawdust. Here, hygroscopic properties also feel important.

Some alternatives I'm considering are Leca, lime gravel, hempcrete, Perlite, and mineral wool.

How have you done it and what were your considerations?

I'd also like to ask what solution you've chosen for the floor?
I think the main options with hydronic underfloor heating are grooved subfloor panels or concrete. Unfortunately, the location of the room means you have to carry buckets by hand if you want to cast concrete, and subfloor panels aren't exactly a favorite material. Am I missing a good alternative?

 

[jhall]

Do you need a solid base for tiling, or are you solving it above? Lightweight concrete like EPS-cement might work well in your case.

 

[cpalm]

Do you need a solid base for tiling or are you solving that above?

I haven't settled on any particular solution, so I'm open to suggestions there as well. EPS concrete is also an option, yes. It feels a bit odd to cast everything in, but maybe it's not a bad idea? I've never worked with EPS concrete, but what I've heard is that it's a pain to mix with those styrofoam balls blowing everywhere. Assuming you then avoid joisting(?), how do you handle the underfloor heating? Do you place it in a thinner regular concrete layer on top?

 

[Pjosk75]

Can only sand work if the construction can handle its weight?
Or Isodränkross/similar? Light and perhaps the mice dislike the coated beads. I suspect that mice like to create tunnels in glass wool/rock wool.

 

[cpalm]

Can sand alone work, if the construction can handle its weight? Or Isodränkross/other similar materials? Light and perhaps the mice dislike the coated pellets. I suspect the mice would gladly make tunnels in glass wool/rock wool.

Sand is also an option. I see no problem with the weight since, as mentioned, it's a concrete floor structure. However, I assume you'd want to top it with something insulating because of the underfloor heating?
Yes, mineral wool is considered not very "mouse-proof."

The question is which of all the options you choose and why? How have you done it?

 

[ArneTW]

I would have used Leca/lightweight expanded clay. Either in loose form or as aggregate in a cement slurry.

/ATW

 

[jhall]

Haven't settled on any particular solution, so I'm open to suggestions there as well.
EPS-concrete is also an option, yes. It feels a bit odd to cast everything in, but maybe it's not a bad idea? I've never worked with EPS-concrete, but what I've heard is that it's a pain to mix with those polystyrene beads that blow around everywhere. I assume you don't need to use studs(?) How do you do it with the underfloor heating? Do you lay it in a thinner layer of regular concrete on top?

Big tub so it's not too bad, underfloor heating in self-leveling compound on top.

 

[cpalm]

Large tub so it's not too bad, underfloor heating in self-leveling compound on top.

Looked a bit cumbersome compared to just pouring on Leca. What are the advantages?
Is it really necessary to frame the floor if you're going to pour a thicker reinforced slab on top of, for example, EPS or Leca? I don't really see what function the joists serve if you're not going to lay something like floorboards?

 

[cpalm]

I will return to this after trying to find more detailed construction solutions. It's probably between EPS and loose Leca as it feels right now.

Specifically, I'm wondering if it's possible to reinforce and float directly on loose Leca and, if so, how to go about it?