Prepare your work surface before you begin. A tray, cookie sheet, plywood or large piece of cardboard can serve as your base. Wet structural mediums such as papier-mâché can cause cardboard to become less supportive, so use cardboard on top of a portable hard surface like plywood. Some reactive elements should only be used outdoors, so be sure that the entire base is portable before you begin.
Experimentation with structural elements is part of the learning process, so make sure to start the project with plenty of time to try a few different kinds. Papier-mâché pulp, homemade papier-mâché, modeling compounds, paper, soil and aluminum foil are a few of the materials you can use. Most structures benefit from a plastic tube in the middle to support the structure. Cardboard may also be used, but plastic does not warp when exposed to liquid and is therefore preferable. Water bottles work well for this purpose.
As with the structure, choosing the materials to fill the volcano affects the style of the "eruption." The most common reactive materials are: baking soda with vinegar; cola with Mentos mint candies, and water added to dry lemon acid mixed with baking soda. There are variations to these: Baking soda can be mixed with soap flakes to create a bigger reaction; red dye added to vinegar makes the eruption look more like lava, and adding starch to the vinegar makes the "lava" flow more realistically. Except in the use of cola with Mentos, add the dry ingredients to the volcano first and then the wet when prepared. With the cola, have the cola ready inside the volcano and drop the Mentos into the cola when ready. Cola with Mentos can be quite messy, so use this one outdoors just in case.
Many of the structural materials will be able to survive only one "eruption." For this reason, test the reactions in another container before using the volcano model. Continue to test the recipe until the reaction is satisfactory. If there is a particular day for the class to showcase the volcanoes, mix the dry materials ahead of time and add the liquid when necessary.