Base (or layers of base materials) under the floor

(See illustration of layers that make up the floor, on page 57).

Reasons for putting a base under the floor:

• Usually the floor needs to be filled in so that it is at least 2 or 3 inches higher than the outdoor ground level to insure it will stay dry. You may have to bring in some fill to raise the floor. It's OK if the floor's base makes the floor higher than the foundation, and makes the floor butt up against the cob walls as long as you've planned for this when placing the doors, and heights of the seats and counters.
  
  
• The base helps the floor to breathe, and therefore keeps it drier. The air spaces between the particles in the base discourage capillary action of water that might sneak in under your floor area.
  
  
• The base is made of stabilizing materials that flex, minimizing the stress on the floor when the ground moves.
  
  
• The base provides a little insulation which speeds up the time it takes the heat to be reflected back into the house.

Moisture barrier between the ground and the floor?

The general rule with natural building is to avoid moisture barriers if possible. With good drainage design and an adequate gravel base, your floor shouldn't need a moisture barrier.

Floor base tests

You can make floor base experiments in 4 or 5 inch plastic potted plant containers. Fill them with the materials you have available, and tamp each layer. Then push them out of the container molds. See which are the toughest. Regardless which base you decide on, tamp, tamp, tamp!