Cardboard chairs are the ultimate way to recycle, using old boxes to create new furniture. While this may sound like nonsense, try this little experiment. Press your hand against the middle of a cardboard box. It squashes pretty easily. But if you press your hand against the edge, it has much more strength. You will take advantage of cardboard's high compression strength to build a chair that can hold 250 pounds or more.
Set a piece of cardboard in front of you with a 36-inch side on top. Measure in 4 inches from the left, then draw a 20-inch line straight down using a carpenter's square. From that point, draw a horizontal line to the right side of the cardboard. This creates a 20-by-16-inch rectangle in the corner of the cardboard.
Cut the smaller rectangle out of the cardboard with a utility knife and discard it. You will be left with an "L" shaped piece of cardboard, which represents the chair's seat and back. The chair will have a 16-inch sitting height and depth and a back that is 20 inches from the top of the seat.
Use this piece of cardboard as a template to trace and cut out the rectangles out of every other piece.
Pour a gallon of white glue into a bucket. Mix in 4 cups of water to make the glue more brushable.
Lay a 24-by-40-inch sheet of half-inch plywood on the ground, then place a thin plastic tarp over it.
Lay the first piece of cardboard on the tarp, centering it in the middle of the plywood.
Brush a thin coat of white glue onto the cardboard with a 3-inch paintbrush.
Lay a second piece of cardboard onto the first, lining up the edges.
Brush glue onto the second piece of cardboard and put a third piece onto it.
Continue building up thin layers of glue and cardboard until all of the cardboard has been used.
Drape a second tarp over the cardboard chair, then place a second piece of plywood onto it.
Place several heavy weights onto the upper piece of plywood to compress the cardboard and glue.
Allow the glue to dry overnight.
Remove the chair from the plywood and tarps. Sand the layered surface with 120-grit sandpaper to remove any glue that has seeped out from between the sheets.