This weekend I will start building a foundation for our wood stove in the kitchen. Under the wooden floor and joists, there is a crawl space, and it looks like there was previously a stove foundation at the site (the floor patched and under the subfloor ends a concrete foundation about 10 cm below the joist bottom). My plan is to saw open the floor and then cast a reinforced concrete slab to level the existing surface (I was thinking about 10 cm thick). Then build up with leca blocks through the floor and finally cast a thinner slab level with the interior floor. Is this the correct way to proceed? How do I seal between the floor and the foundation?
For a wood stove, you hardly need to cast a foundation for load-bearing purposes, as most cast iron stoves weigh under 100kg. If you then build with leca (or why not lightweight concrete?), you keep the weight down further. I have a similar solution as you, the foundation built from the crawl space. I placed sill paper between the foundation and the studs I attached the joists to around the foundation. Otherwise, I didn't seal more than what was done with insulation and wind paper. When the wooden floor was laid, I laid it tightly against the foundation over the floor. I filled the gap between the floor and the foundation with plaster when I was plastering the foundation anyway. (It got a bit messy, ask if you don't get it ;-)
Ok! The reason I want a foundation is that the floor gives way a bit right where I plan to have the stove, and I also want to partially build with bricks to get some heat storage. The difference is that I already have a floor that will remain, and the slab will be cast through the hole I saw open. But it should be possible to do it the same way.
Yes, I agree with you. Moreover, it's not wrong to make it steady. If it's an old torpargrund, it's convenient to avoid dismantling the stove if you need to tear down the floor and the joists. (I've done just that myself). How much space do you have in the foundation since you need to build up with lecablocks? Since you are casting the last piece, perhaps you can make the mold a bit neat and line it on the inside with sill paper, and let it remain after casting, then you have every opportunity to create a nice transition between the mold and the floor.
Oh, I see! Myself, I had 20 cm to work with and didn't need to redo the foundation. Good luck.