Can walls are a way of making non-structural walls in earthships or other ecologically-friendly buildings. Aluminum or steel cans (or sometimes glass bottles) are stacked on their sides like bricks, with concrete or mortar holding them together.
I decided to use both methods to make a small fire pit for the back yard. It's crumbled a bit since I think the fire got too hot and burned out some of the paper and making it weaker, but these construction methods would work well for any structure that isn't on fire regularly and doesn't need to fit building codes. Since this structure didn't work too well as a fire pit, I plan on using it as a planter in my garden come springtime.
Right now, there are only a few city building codes in the US that allow for the use of papercrete, but if you live in unincorporated land or are building something like a dog house, then go for it!
Step 1: Drink a lot of soda, or eat a lot of soup
You will also need dirt or sand, some cement, and a bunch of shredded paper. I got shredded paper from my home and from offices, but if you have a way of pulping or shredding paper yourself, you can use any kind of paper. I've heard that glossy magazines and ads work well, since they contain clay.
For tools, I used a five-gallon bucket, a shovel, the broken handle from a snow shovel, and my hands. For best results, you should have a power drill and a paint or plaster mixing attachment to pulp the paper, but I found that simply mixing everything together worked well (until it caught fire, that is).
You might want some gloves for working with cement, since it is quite alkaline.