These can be set into a silty or sandy soil layer. Put the flattest sides up. The stones can be laid with or without mortar between them. You can use a cob, soil cement, or concrete mortar to fill in the spaces between the stones or bricks. (See the section on mortars in the chapter on foundations, pages 50-51.)
Bricks are expensive if you buy them new. See if you can scrounge up some used ones. Old bricks have become popular and are harder to come by than they used to be. Good luck! Bricks can be used with or without mortar. They can be laid slightly crooked to each other to create a flowing pattern that will suit organic-shaped walls better than the usual parallel rows.
Some earth floors are made thicker and with a heavy clay content. This type of floor is often wetter and is poured into the house. If it is wet enough, it will level the surface itself like water would. Some folks mix the floor right in the house, throwing the ingredients in, adding water, and treading it in place in a big, muddy party.
This kind of floor is allowed to crack up naturally and then the cracks are filled in with a different colored mortar to create a flagstone look. The partially hard floor can be cut into tiles or shapes to give it a controlled place to crack, and then those cracks can be filled. The 'grout' or mortar can be thinned down and drizzled from a pitcher or tin can into the cracks.
This type of floor is usually 4 inches thick, either poured all at once or in two 2 inch
layers. It will take a long time to dry - so if you live where the humidity is high, you'll probably want to decide against this kind of floor.
A floor can be made of rammed earth. Cob ingredients (minus the straw) are mixed well and laid down almost dry (ever so slightly moist) onto the floor base. Tamp the earth really well with a flat tamper. A good floor tamper can be made by welding a 12 inch (or less) square flat piece of steel onto a steel pipe, or by screwing a 12 inch (or less) piece of plywood to your wooden tamper. I suggest you make tests in potted plant containers and see what you think. An advantage to this type of floor is that it will dry quickly. Although it is not as durable as a cob floor, it is good under tile or carpets.
(See page 52 in foundation chapter for more about soil cement.) Make up test batches as if you are mixing cob, but add different amounts of cement to the dry ingredients. You'll probably want a soil cement floor to be at least 4 inches deep. Try tamping some of the tests. Dry the samples. Did they crack? Are they strong enough to walk on? The surface can be cut, printed, or pressed to look like tiles or shapes. The spaces between the tiles can be filled with a different colored soil cement to look like grout. Soil cement can be used to make tiles. Both these tiles and the poured soil cement can also be used for the floors of patios and porches.
You can use a rototiller to make soil cement floors (or even roads) if you have a sandy soil. Figure on making them 5 inches deep. Calculate how much cement to add (6 to 10%) to each square yard or meter.
Sprinkle the cement on and mix it all up dry with the rototiller. Then spray it with water and rototill it again. You can tell if you have the right amount of water if you can squeeze it into a ball and it holds together, and if when you break the ball in half, it doesn't crumble. Then rake it smooth and tamp it well. Remember to let it cure slowly.
Tiles make a very beautiful flooring. They are expensive in some places. You can always get seconds or broken tiles and make a mosaic floor. Broken organic shapes look great with the rounded walls. You can make your own tiles out of soil cement, fired clay, concrete or even wood.
To make a loft or second-story floor, simply bury the supporting beams and/or joists into the cob.
You may want to put the floor in as you build. That way, where the cob wall and the floor meet, the squared ends of the floor boards will be buried in the cob wall. This makes the finishing work easier than cutting curves on all the boards if you put the floor in later. The floor will serve as a scaffolding while you cob the second story. Protect it so it doesn't get wrecked during construction.
I have never built a wooden floor on the ground floor of a cob house. To me that would waste the opportunity to have a thermal mass floor that offers heat storage. It would also use precious wood. If you do decide to make a wood floor you might want to consider the following: