Papercrete is a lightweight concrete made with paper products instead of gravel for the aggregate, which helps to stretch out the cement used in traditional concrete mixes. Cardboard is readily available, often as a discarded material, and as such is a favourite of papercrete makers. While less strong than traditional concrete, you can still use papercrete as a valid and inexpensive building material, especially in single story structures. The mixing process is much the same as with traditional concrete with a few minor changes necessary to prepare the cardboard for use with the other concrete ingredients.
Add a small layer of water to the bottom of the bucket, about 2 inches in depth. Cut the cardboard to fit into the bucket and then add to the water, allowing the cardboard to soak up the water until damp. Attach a mixer bit to an electric drill and apply the bit to the cardboard, breaking up the dampened material into pulp. Continue until you have a full bucket of the pulped cardboard material.
Combine the pulped cardboard, sand and cement in a second bucket to create your cardboard papercrete. Use a mixing ratio of 60 per cent cardboard, 30 per cent sand and 10 per cent Portland cement. Mix the materials with the electric drill mixer attachment until you create a thick, barely moist mix.
Add water to the mix, thinning out the papercrete as you continue to mix it into a usable consistency. You want to create a thick low-slump mixture for building use. Test the consistency by filling a paper cup with the mix and then placing the cup onto a flat surface. Lift the cup and watch the papercrete for movement. A usable batch should retain its shape without crumbling.
Run the cardboard through a paper shredder for best results when pulping.
Cardboard papercrete is not waterproof. If used in a moisture rich environment, seal with concrete sealant after the material cures.