How to make a plaster volcano with a plastic bottle

Written by charles clay
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How to make a plaster volcano with a plastic bottle
A model volcano is a fun and easy science fair experiment. (Brand X Pictures/Brand X Pictures/Getty Images)

A model volcano is a classic science fair project. This version uses a plastic bottle as a chamber for mixing the vinegar and baking soda. The bottle will protect the inside of the volcano from the "lava," which will increase the number of times the experiment can be carried out before the volcano begins to deteriorate. The plastic interior of the bottle is also easy to clean between eruptions.

Skill level:
Moderately Easy

Things you need

  • Plaster of Paris
  • Cardboard box
  • Scissors
  • Tape
  • Scrap paper
  • Paper towels
  • Hobby paint
  • Baking soda
  • Vinegar
  • Dish soap
  • Red food colouring

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  1. 1

    Cut the top off of the cardboard box, leaving an inch or two of the sides to form low walls. Cut the rest of the removed cardboard into long, narrow strips.

  2. 2

    Tape the cardboard strips to the top of the bottle, just below the neck. The strips should form an open cone around the bottle. Tape the free ends to the bottom of the box so that they secure the bottle to the cardboard and hold it upright.

  3. 3

    Fill the area between the bottle and the cardboard strips with balls of wadded-up scrap paper.

  4. 4

    Mix 2 cups plaster of Paris with 1 cup water. Dip strips of paper towel into the plaster and paste them to the cone. Continue until the cone is completely covered, leaving the bottle's mouth open. Allow the plaster to dry.

  5. 5

    Paint your volcano. Traditional volcano colours feature a brown body with a rim of red around the top to suggest lava.

  6. 6

    Add a tbsp of baking soda, five or six drops of dish soap, and a few drops of red food colouring into the plastic bottle. Add water to the mixture. Filling about a quarter of the bottle will result in a relatively small eruption, while leaving just enough room for the vinegar will provide a large amount of lava. When you are ready for the volcano to erupt, add a 1/4 cup of vinegar.

Tips and warnings

  • For a more natural-looking volcano, use several layers of plaster-soaked paper towels to create a lumpy, rugged-looking surface.
  • Kids should never use scissors alone. An adult should always help with cutting up the cardboard box.
  • This model is designed to spew red, foamy liquid. Make sure you leave enough of the sides of the box to catch the overflow, and don't perform this experiment on any surface that can't be cleaned.

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