Finishing up a grueling multi-round epic of various concrete and earth pours, we have finally finished! Did I mention I hate concrete? Ya.
First we laid down 6mil polyethylene plastic sheeting as a vapor barrier. The barrier extends over the edge of the stem wall to give the sill plates a vapor barrier as well. Next went on the insulation. We used R-Max 1.5" rigid foam board from Home Depot. HD has cheaper stuff but we went with this one since its a tighter more uniform foam that has a lot more compressive strength. At the edges, pieces of foam were beveled at a 45 degree angle giving the slab total isolation from the ground and very good insulation. We are aiming to passively solar heat the house during the winter and this should go a long way to keeping heat in the floor.
Little unorthodox and probably not recommended but we loaded the slab with small pieces of broken up concrete (also referred to as urbanite). We figured as long as there was space in between the pieces for our mix to fill up, it'd probably be fine...probably. The concrete pieces helped us recycle more of the old patio slab and lessened the amount of material we had to pour. We also placed 6" square welded wire mesh within the slab (scored this for free on Craigslist).
The slab is a mix of clay/sand/silt from on site, aggregate from on site and collected from Freecycle and cement. The mixing was by no means scientific but cement comprised only about 1/15th of the mix by volume. We felt some creative liberty in our methods given the floor has zero structural requirements and just needs to be solid enough to walk on. The bottom mix is aggregate rich and uncolored while the top layer is a mix of fines and has red pigment powder added to it; this will be our finished floor
Looks pretty good! It definitely has some "character". We did a terrible job of leveling it which is going to make putting in furniture and cabinets hellish (oh well). The mix is going to take a long time to fully dry so the color should even out and become lighter in time. Its surprisingly strong for being mostly earth. Of course not as strong as concrete but it is fortunately easy to repair if needed.
Next step: framing!
Looking forward to getting some walls up!