How to Mold Plastic

Molding plastic is a fun, inexpensive way to create unique pieces or replicas of your favorite items. You may purchase a mold or create your own custom molds out of reusable molding materials, silicone, and or plaster. Cast your mold with plastic resin, wait for it to cure, and then remove the mold to reveal your creation.

Method 1
Method 1 of 4:

Making a Mold from Reusable Materials

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  1. The master part is the item that you will use to create the mold.
    • To prepare the master part, first wipe down or wash the item.
    • Once clean and dry, apply a release agent to the original item—this will ensure that the master part will pop free from the mold.
    • Coat the item with a layer of bubble buster—this product prevents the formation of air bubbles around the master part.
    • Place the master item into a heat safe container. The container must be slightly larger than the item.
  2. Reusable molding material is easy to use and mistake proof; you can melt, mold, cast, and de-cast reusable molding material up to 35 times. Place the container of reusable molding material into a microwave. Follow the instructions on the product to properly melt the materials.
    • Heat the material for short intervals, roughly 15 to 20 seconds, until you understand how the microwave affects the materials.
    • If you do not have a microwave, you may use a double boiler.
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  3. Carefully pour the melted molding material over the master part. Allow the product to cool and harden. Gently remove the mold from the heat safe container and the master part from the mold.
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Method 2
Method 2 of 4:

Making a Silicone Mold

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  1. When a high concentration of dish soap is combined with water, it forms a catalyst bath for silicone—it allows the silicone to cure faster. In the large bowl, combine approximately 64 ounces of water with 4 ounces of blue dish soap. Mix the soap and water together with your hands. [1]
  2. Use a pair of scissors to cut off the tip of the 100% silicone. Insert the bottle into a caulk gun. Empty enough of the 100% silicone into the catalyst bath to surround your master part.
    • If you are unsure how much you will need, use the entire bottle of 100% silicone. [2]
  3. Submerge your hands into the catalyst bath and slowly gather the strings of 100% silicone into a ball. Massage the ball with your fingers. Pull, stretch, and fold the 100% silicone as you knead it. Continue to knead the 100% silicone until it stiffens and becomes less malleable. [3]
  4. Retrieve your master part. Carefully flatten out the 100% silicone so that it is ½ inch thick. Cover the master item with the 100% silicone—press the 100% silicone into all of the knocks and crannies of the master part. Once you have formed the mold, attempt to wiggle the master item out and back into the mold. If you can easily achieve this, the mold is ready to cure. If you can not, reform or cut away parts of the mold. [4]
    • Applying a release agent to the master item will make it easier to remove from the mold.
  5. Pour soapy water onto a paper plate so that it just coats the surface—this will prevent the silicone from adhering to the plate. Set your mold and master item onto the plate and allow it to cure for 1 hour. When the mold is no longer tacky to the touch, remove the master item.
    • While the mold is curing, it is essential that the master item remain within the mold. [5]
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Method 3
Method 3 of 4:

Making a Two Part Mold

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  1. The separate sides of a two-part mold join along the centerline of the master object. Retrieve your master item, a permanent marker, and a ruler. Draw a straight centerline around your master item. [6]
  2. Set a block of non-toxic and non-drying molding clay on your work surface. Embed the master item into the clay up to the centerline. The top of the item should line up with the top of the clay bed. There should be a 1 inch border of clay surrounding the remaining 3 sides of the item. [7]
  3. Alignment keys join the 2 halves together perfectly. Retrieve four ½ inch alignment keys and a bottle of temporary adhesive. Apply a thin layer of temporary adhesive to the flat side of the alignment key. Place the key in ¼ inch from the top left corner and adhere it directly to the clay. Place 1 key in each of the remaining 3 corners. [8]
  4. In order to fill the mold, you must provide an opening. For this mold, the opening will appear at the top of the clay bed. Apply a thin layer of temporary adhesive over the top of the master item—the side not embedded in clay—and the top side of the clay bed (the side directly below the top of the master item). Press this side flush against a wooden or metal retaining wall. Allow it to dry. [9]
  5. A layer of silicone mold putty will form 1 of the mold’s inner walls. Coat the master part with a release agent. Apply a layer of mold putty to the exposed half of the master item. Apply mold putty to the clay bed’s surface, carefully covering the alignment keys. Extend the molding putty ½ inch up the retaining wall. [10]
  6. Apply a thin layer of temporary adhesive to the bottom side of the clay bed (the side parallel to the top of the master item). Press this side flush against a wooden or metal retaining wall. Allow the adhesive and the molding putty to cure for 1 hour. [11]
  7. Due to the flexibility of cured molding putty, it is necessary to create a second more durable shell, known as a mother shell. You will create the mother shell with plaster sheets.
    • Cut 4 to 6 sheets of plasters. Each sheet should be 6 inches longer than the mold.
    • Layer the sheets on top of eachother. [12]
    • Dip the sheets in bowl filled with room temperature water for 1 second.
    • Remove the excess water by squeezing the sheets over the bowl. The sheets should be wet, not dripping with water.
    • Lay the sheets over the mold and up the retaining walls.
    • Press the sheets into the mold so that they form to the shape. Crease the edges along the retaining walls into crisp 90° angles—the plaster sheets lining the retaining walls will serve as feet. [13]
    • Allow the plaster to cure for 30 minutes. [14]
  8. Once the plaster has hardened, remove the two retaining walls. Flip the entire mold over so that it is resting on the 2 plaster feet. Carefully remove the clay bed and any remnants remaining on the master part.
    • If the key alignments do not come off with the clay bed, remove these as well. [15]
  9. When creating the second half of the 2 part mold, you will repeat the process you just completed:
    • Apply a release agent to the master part.
    • Attach the top of the mold to a retaining wall.
    • Coat the master part in a layer of molding putty.
    • Attach the bottom of the mold to a retaining wall.
    • Create a mother shell out of plaster sheets. [16]
  10. Once the plaster has cured for 30 minutes, you can safely disassemble the mold. Remove the two retaining walls from the mold. Place the mold upside down on your workspace. Remove the mother shell and carefully peel away the silicone mold. Set aside the master part and reassemble the mold. [17]
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Method 4
Method 4 of 4:

Casting the Mold

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  1. Find a flat work space that is well lit and ventilated. Cover the work space with clean paper towels or scrap paper.
    • Newspapers are not advised as the print could come off on your molds or your finished plastic parts.
    • You may also cover the surface with a trash bag or an old vinyl tablecloth. [18]
  2. Proper treatment of the mold is essential to the success of your project.
    • If you are using a pre-made mold, wash it thoroughly under hot water to remove the film of cornstarch. Dry it with a clean cloth.
    • Coat your mold with a layer of release agent.
    • If you are using a 2 part mold, coat both sides and reassemble it. [19]
  3. Plastic resin is comprised of 2 parts, typically labeled part A and Part B. The resin is formed by mixing equal parts A and B.
    • Retrieve 2 plastic disposable cups.
    • Determine how much resin you will need to complete your project.
    • Pour equal parts A and B into cups 1 and 2 respectively.
    • Pour the contents of cup 2 into cup 1.
    • Stir with a wooden popsicle stick. [20]
  4. Pour the resin into your mold. To combat the air bubbles rising to the surface, spray the top of the resin with a releasing agent. Smooth and scrape off any excess resin with a metal putty knife. Allow the resin to set for the time specified in your product’s instructions. [21]
  5. Once the resin has set, you may carefully remove the item from the mold. If you are using a pre-made mold, a silicone mold, or a mold made from reusable materials, apply pressure to the back of the mold with your fingers and pop the item out. If you are using a 2 part mold, disassemble the mold to remove the item. [22]
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Expert Q&A

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  • Question
    Is there an edible mold?
    Mark Weiser
    Artist
    Mark Weiser is an Artist and Gallery Manager for DKW Art Gallery based in Marion, Iowa. He and his wife Deb manage the gallery, which boasts a variety of art, including paintings, ceramics, and photography. The gallery also provides art classes for the community, hosts shows, and runs events that build awareness of regional artists of all ages. Mark has also owned and operated art galleries in Florida and Georgia. He creates carved slate and wood pieces inspired by Irish and Celtic art, featuring the Gaelic language done in the ancient Ogham alphabet. Some of Mark's previous clients include CNN, Pinnacle Bank, and Collins Aerospace. He received a BS in Business Administration with minors in Education and Psychology from Emporia State University.
    Mark Weiser
    Artist
    Expert Answer
    Yes, and chocolates are a great example! There are molds that are specifically designed for shaping melted chocolate into fun or fancy designs that you can eat. They're usually made from food-safe materials like silicone or hard plastic, so they're safe to use with chocolates.
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  • Question
    Where can I buy the materials?
    Community Answer
    Any kind of hobby or craft store should have them, like Michaels or Hobby Lobby, but you could also check places like Amazon if you aren't able to find the materials in stores.
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  • Question
    What material would I use to make a custom master item to make molds from?
    Community Answer
    You can use metal (brass or iron) as molds. They will help to form plastic molds.
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      Tips

      • New molds will typically come with a thin layer of cornstarch inside to keep them from sticking to each other. It is usually suggested that you sprinkle them with cornstarch before storing for long periods of time to protect them.
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      • Check with the supplier of your liquid resin to find out how much it will shrink as it hardens. This would be very important to take into consideration when making objects to scale.
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      • You can speed drying time up by using a hand held hair dryer set on low. Do not hold it in 1 position—instead move it back and forth over the surface of the plastic mold with a sweeping motion.
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      Warnings

      • Work in a well ventilated area when mixing and pouring the plastic resins.
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      • When making molds, take care not to use copyrighted objects as the basis for your mold. Some of the most common copyright infringements occur with cartoon characters, so be careful.
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      Things You'll Need

      Making a Mold from Reusable Materials

      • Reusable molding materials
      • Microwave or double boiler
      • 1 heat safe container
      • Mold release agent
      • Bubble buster product
      • 1 master part
      • Spoon

      Making a Silicone Mold

      • Water
      • Blue dish soap
      • 100% silicone
      • 1 large bowl
      • Caulking gun
      • 1 master part
      • 1 paper plate
      • Scissors [23]

      Making a Two Part Mold

      • 1 permanent marker
      • Ruler
      • 1 master part
      • Non-toxic and non-drying molding clay
      • 4 alignment keys
      • Temporary adhesive
      • 2 wooden or metal retaining walls
      • Silicone mold putty [24]
      • Plaster sheets
      • 1 large bowl
      • Room temperature water [25]

      Making a Two Part Mold

      • Mold(s)
      • Paper towels or scrap paper
      • Resin Mix
      • Release Agent
      • 2 disposable plastic cups
      • 1 popsicle stick
      • Putty Knife [26]

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      References

      1. ↑ http://makeitatyourlibrary.org/living-play/worlds-easiest-silicone-mold#.Vl28VGSrS2w
      2. ↑ http://makeitatyourlibrary.org/living-play/worlds-easiest-silicone-mold#.Vl28VGSrS2w
      3. ↑ http://makeitatyourlibrary.org/living-play/worlds-easiest-silicone-mold#.Vl28VGSrS2w
      4. ↑ http://makeitatyourlibrary.org/living-play/worlds-easiest-silicone-mold#.Vl28VGSrS2w
      5. ↑ http://makeitatyourlibrary.org/living-play/worlds-easiest-silicone-mold#.Vl28VGSrS2w
      6. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      7. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      8. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      9. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      1. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      2. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      3. ↑ http://www.makeyourownmolds.com/how-to-make-mother-mold
      4. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      5. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      6. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      7. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      8. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      9. ↑ https://www.youtube.com/watch?v=1H42C3nW_nw
      10. ↑ https://www.youtube.com/watch?v=1H42C3nW_nw
      11. ↑ https://www.youtube.com/watch?v=1H42C3nW_nw
      12. ↑ https://www.youtube.com/watch?v=1H42C3nW_nw
      13. ↑ http://www.hirstarts.com/casting/plastic.html
      14. ↑ http://makeitatyourlibrary.org/living-play/worlds-easiest-silicone-mold#.Vl28VGSrS2w
      15. ↑ http://www.makeyourownmolds.com/how-to-make-two-part-mold
      16. ↑ http://www.makeyourownmolds.com/how-to-make-mother-mold
      17. ↑ http://www.hirstarts.com/casting/plastic.html

      About This Article

      Article Summary X

      Before molding plastic, start by washing or wiping down the item you’re using so that you end up with a mold without bumps or unevenness. Once the item is dry, apply a commercial release agent to ensure that it will pop free from the mold. Then, coat it with a layer of Bubble Buster to prevent air bubbles before placing it in a heat safe container. Afterwards, melt the reusable molding material in the microwave and pour it into the container to create the mold. Finally, remove the mold from the container once the molding material cools and hardens. To learn more, including how to mold plastic items using silicone, scroll down.

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