We met a man who had a rammed-earth home. He was fascinated by the "green" idea of taking old tires and recycling them into a structure. I think they did it in NM and the finished home was stunning. He said he started with the idea it would not only be a good green project but also cheaper than conventional stuff.
The base of the structure is tires with dirt pounded into the cavities, then you use the tires to make a thick, well insulated wall. Anyway...... the tires are free, so how bad can this cost get? He said he had a big piece of land so the dirt was also free ..... so how bad can this cost get? Well ..... he had a line-item for wages and marajuana for the dirt-pounders that ran this construction method up about 50% over conventional construction. I think the lesson on a lot of this earth-ship stuff is that it is labour intensive. In a place where people work for pennies a day and there is lots of extra dirt and/or sand, maybe it makes tons of sense, but in other places the economics just don't work. Even the bullet-proof house project in Nigeria (plastic bottles with sand in them) began to run into source-of-sand issues.
So...... going green and recycling - YES, fantastic! But think it through all the way before you start. The devil is in the details. I like the ideas - and the end product can be tons of fun --- but the enthusiasts often overlook local circumstances and waste a lot of time.