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Learning to cast and finish plaster is a skill that both Cub Scouts and parents will enjoy. When you start a plaster casting project, be sure to cover your table or work area with newspaper. Plaster can be messy and sticks when it hardens.
Discarding leftover plaster is a problem unless you follow some simple rules. Allow dried plaster to soak loose from mixing pan and pour into disposable container. When plaster is dry, throw away. DO NOT POUR DOWN THE SINK DRAIN.
Plaster of Paris comes in bags, 5 pounds or larger. You can purchase it at hardware or paint stores.
Other materials needed are:
¥ Water for mixing
¥ A mixing container
¥ A soap solution or grease to keep molds from sticking
¥ A mold
¥ Newspaper to cover your work area.
Use the type of mold best suited for your project. Commercial molds, made from flexible vinyl or latex, plastic, or plaster are available in many shapes and sizes. For special projects, try improvising your own molds from wood or cardboard, cookie cutters, sand or molding clay.
Prepare your mold to prevent sticking. Use grease or oil for all molds except latex and a soap solution of 1 cup of water and 1 tablespoon of liquid detergent for latex molds.
To mix - pour water into container. Use amount equal to size of mold. Sprinkle plaster slowly into water until a peak forms above the surface and allow to sit for 1 minute. Stir gently to avoid air bubbles until plaster resembles heavy cream. Do not mix more plaster than you can use quickly. Plaster hardens in 3 to 5 minutes.
Pour plaster immediately and work it into crevices with a toothpick or old paintbrush. Fill larger molds three-quarters full, flex molds with your hand, fill to top and flex again.
Let plaster stand 15 to 30 minutes for smaller molds. Remove mold. Larger molds take 1 to 2 hours.
Sand rough edges.
To finish, allow to dry completely, from 1 to 3 days. Where air bubbles have formed , scrape gently with a small knife. Make a thin solution of plaster and water and fill in the cavity. After repair hardens, smooth with fine sandpaper.
Decorate with watercolor, tempera, poster paint. Glaze with varnish, lacquer or clear figure glaze. Tint with food coloring.
Making Your Own Mold
Modeling clay is a good base for molds for simple shapes such as neckerchief slides. Press model to be reproduced firmly into clay and remove gently. Oil the clay but do not use a soap solution. Fill with plaster and allow to dry.
Waxed cartons - Do not grease or soap as the wax will serve the purpose. Fill mold with plaster and press a small bottle into plaster to make a depression for an ashtray or a candleholder. Allow large cast to set several hours.
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