Around here (central OK) D.O.T "ag-base" or road base is basically recycled concrete from old roads, etc. Finding what a 'normal' permie (oxymoron???) would call "road base" around here is nigh near impossible. The closest I've found is decomposed granite (love the stuff, but the closest to us is 3 hours away). The question becomes, how far can one deviate from purity when it comes to creating an earthen floor? The second question becomes, what else might one use? We're interested in basically a tamped floor with the option of tile, etc. on top. Our original plan was gravel over tamped grade (4"), then road felt, then decomposed granite and a thinner finish of troweled cob and tile, etc. Now, funds are short. If you've read any of my questions before, you may have gathered that we've had a long line of "unexpecteds" and crazies happen since the beginning of our building fitjourney and they have drained our resources. Now we find we need our house to be done. DONE. And I need practical ideas. Yes, I have the book. Whichever one you want to reference. Yes, I've read that article. I promise. Now my brain is smoking and I need your input.
I have seen many people use soil-cement floors with great success. Till in some cement into the first few inches of soil, get it damp, tamper it down and let it dry. It ends up being a nice semi-waterproof (the more cement, the more waterproof) flat surface that you can put whatever you want on top — wood flooring, tile, cob, etc.