How to Make a Foam Volcano

Take a piece of 1/2-inch-thick wood plank and cut it into a 1-foot square with a handsaw. Use a bench vise to steady the wood plank. Place a plastic liter bottle of soda in the middle of the wood plank and draw an outline of its bottom on the wood plank with a felt pen. Use a drill and hole saw bit to cut out a circular pattern in the wood plank, so the bottle can slip through it.

Lay the wood plank on a flat work surface. Wrap the entire bottle in tin foil up to the neck. You may drain the soda into another container if you wish to easily wield the bottle. Save the soda, though, and pour it very slowly when transferring it.

Set the bottle upright in the middle of the wood plank, inside the hole. Take a can of spray foam, like Great Stuff, and spray the bottle from the base up, covering it completely. Spray the heaviest concentration on the base and work your way up, creating a cone. Leave an opening in the top, so the bottle neck is accessible. Let the spray foam dry completely, according to the manufacturer's directions.

Paint the volcano your desired color, using a brush and any household paint. As an option, you might wish to use spray paint. Let the paint dry completely. Pull the soda bottle from underneath the wood plank, and replace the soda, if you have removed it.

Set the full bottle back underneath the volcano cone. Use a funnel to drop three Mentos candies into the top of the bottle neck. Watch the foaming eruption -- it will be quite dramatic. Reload another fresh soda bottle to repeat the demonstration.