Cardboard Boat Building Tips
The fun is in the discovery. So, here are some boat building tips. Now go for it! Be creative. If you can dream it, you can do it.
- Use un-damaged cardboard. If you break or crush or cut through the corrugations, the cardboard may fail while in use. Don’t step on your cardboard!
- Use water-based wood glue.
- Use a roller to spread the glue over large surface areas, and remove excess glue. Excess glue can damage the cardboard and take too long to dry.
- Clamp or use weights to press the glue joints and layers together. Be sure to use a large flat surface in between the clamp or weight and cardboard. This will protect the cardboard corrugations from damage.
- Keep your cardboard dry! Seal the open edges with silicon sealant (use a water-soluble type if possible as it makes for easier cleanup). Remember to seal the ends of the cardboard with caulk or silicone, or you’ll have great fun watching the water draw up into the corrugations just like in a drinking straw. This could cause premature failure.
- Use paper tape to help join pieces of cardboard. Duct-tape shrinks when it is painted and it also shrinks differently than the cardboard.
- Reinforced paper tape works well over caulked edges and seams. Use the tape to cover and reinforce joints and any “open” ends of the cardboard.
- Layer cardboard for additional strength. Try layering the cardboard with the corrugations going in different directions. This will make for a stronger laminate. You can have strength and still keep your boat light if you place the second layer so that the corrugations run at a 90-degree angle to the first layer.
- To fold cardboard across the corrugations, consider scoring the line of the fold with the butt end of your utility knife or other rounded edge of a tool.
- Try to build the raft in a warm, dry, low humidity location. This will speed up the glue drying process.
- Use water-soluble outdoor latex-based primer for the initial coats of paint. Avoid oil-based paints, stains, caulk, and glue because the oil soaks into the cardboard, which weakens and damages it. The cardboard may never dry!
- Try building a model first. Scale down your design and cut its “flat-pattern” shape out of a manila folder. Use stones or small weights to test the buoyancy. Tape together and seal it from the water using scotch tape. This could give you an idea if the boat will float the way you want.
- Remember to decorate your boat (highly rewarded by the Judges) and to bring your own wooden paddles or oars. Double bladed paddles are not acceptable.
- Be sure your boat will be able to get out the door of wherever you build it!