Re: adobe for sculpting
I had an adobe house for years. What Andrew says is right on. You need long overhangs on the roof, and you paint on a sealer at least once a year. I used an acrylic sealer. Out in the sticks they use burro shit and water.
The guys who made the bricks used a clay/sand mix, basically the same thing they use for fired brick.
We have been building some schoolhouses here using something we call Eco-block. It's dirt and cement mixed with a bit of water and rammed in a press. It seems to be pretty weather resistant.