This article was taken from the December 2014 issue of WIRED magazine. Be the first to read WIRED's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.
Tools and materials
- 500ml bottle of polyurethane glue
- Carving knife
- Sandpaper
- Pozidrive screwdriver
- 4x 1m cubes of polyurethane foam
- 80 metres of 3mm-diameter steel wire
- One standard ball of string
- One hundred 50mm Pozidrive screws
- One 25kg bag of cement
- 35 litres of water
- 350 litres of 2mm-diameter hollow glass beads
- 5 metres x 3 metres of plastic sheeting
- One 5-litre tin of wood stain
- Bolt cutters
Make a mould First you need to make a mould for your canoe -- a positive mould where the canoe is moulded over the outside, not in a hollow. Glue the foam cubes together to create a 1m x 1m x 4m block. Once the glue has set, use the knife to carve the block into the shape of an upside-down canoe. Then sand it smooth.
Reinforce it Use steel wire to reinforce it. Insert the screws 20mm deep into the foam, set 100mm apart, in ten rows per side of the mould. The first row should start 10mm from the bottom of the mould; leave 9mm of space between rows.
Use the string to tie a 4m length of the wire to each row of screws, halfway between the foam and the protruding screw.
Mix the concrete Consider adding a polymer, such as latex, to increase the flexibility and bond strength of the mix. The more flexible the concrete, the more stress will be transferred to the reinforcement. Combine the bag of cement with the water and slowly add the beads until the consistency is like soft clay so it will stick to the mould.
Cast it Scoop handfuls (wear gloves) of the mix and stick them to the mould; get the mixture in between the foam and the reinforcing wires to ensure they are embedded in the concrete. Keep doing this until your mould is covered with concrete to the depth of the screws. Wrap the canoe in the sheet -- this stops it drying and cracking.
Finish it up It will take a week for the concrete to set. Remove the sheeting and sandpaper the hull. Keep applying the wood stain until you finish the tin. The canoe can now be turned over and the knife used to cut the foam mould from the finished hull. Watch out for the screws sticking out of the concrete -- just trim them off with bolt cutters.
Float your boat Float your canoe on a small pool -- once you're sure it's watertight, fill the inside of it with water. If you want to enter a concrete-canoe competition your craft must continue to float just below the surface when fully flooded. Remember that foam blocks can be added if you think that yours needs them.
This article was originally published by WIRED UK
