Making a Two-piece Silicone Mold for Casting Plaster

Today's tutorial records the process of casting gypsum material by making a two-piece silicone mold, which is suitable for making silicone molds for more complex models such as small statues, toys, and decorations.

two-piece silicone mold

Tool & Material

1. Mold making silicone

2. Release agent

3. Silicone pigment

4. Plasticine

5. Hot melt glue and glue gun

6. Acrylic plate

7. Measuring cup

8. Electronic scale

List of tools and materials


Step 1: Fix the master pattern: First of all, we need to firmly fix the master pattern on the flat plate to prevent the master pattern from shifting after pouring the liquid silicone. Here, use plasticine to fix it, and press half of the height of the master mold into the plasticine.

fixed master pattern

Step 2: Set the pouring port: After the silicone mold is made, the gypsum material will be injected into the mold cavity from this hole, usually the injection hole and the exhaust hole. It doesn't matter if the vent hole can be a little smaller.

setting Sprues and Vents

Step 3: Build the box: Silicone is a fluid liquid, so we need to build a square box with acrylic boards around the master pattern mold, and seal the surrounding interfaces with hot melt adhesive.

build the box

Step 4: Set the positioning hole: The function of the positioning hole is to facilitate the two-piece silicone mold to be combined and fixed more closely. Usually, a small round wooden stick is used to press lightly on the plasticine.

set the positioning hole

Step 5: Apply mold release agent: Spray mold release agent on the master pattern and plasticine for better separation and mold release after curing.

apply mold release agent

Step 6: Prepare the silicone:

First of all, we need to determine the amount of silicone. We can use loose things such as sand and millet to fill the mold frame, then pour it into a measuring cup and determine the amount of silicone required. In practice, the loss should be considered. Increase the volume by approximately 10-15% to calculate the amount of silicone.

Mixing silicone: According to the instructions on the silicone package, weigh the A and B parts of the silicone according to the ratio, then mix the A and B parts together, and stir well. If you need to change the color of the silicone, you can add silicone color paste Stir together.

stirring liquid silicone

Step 7: Pour the silicone: Carefully and slowly pour the prepared silicone onto the master pattern, so as to cover the highest point of the master pattern by about 2 cm.

pour the silicone

Step 8: Wait for curing: Put it on a flat table and let it cure at room temperature. Usually, most rtv silicone can be cured in about 24 hours. Of course, this is also related to the amount of curing agent and temperature you add.

check whether the silicone is cured

Step 9: Disassemble and separate: Remove the box and remove the plasticine, so that half of the silicone mold is completed.

remove plasticine

Step 10: Make the other half of the mold: Turn the completed silicone mold upside down as shown, and surround it with acrylic sheets.

make the other half of the mold

Step 11: Apply the mold release agent: This step is necessary to spray the mold release agent, because the silica gel is easy to be in direct contact with the silica gel, and it will be very strong and difficult to separate.

apply the mold release agent

Step 12: Repeat steps 7 to 9 to complete the other half of the silicone mold.

remove the formwork

separate silicone mold

Step 13: Clean the mold: Wash the plasticine and other residues remaining on the silicone mold with water and dry it.

clean plasticine from silicone molds

Step 14: Assemble the Moulds: Assemble the cleaned two-piece silicone moulds and secure them with straps.

combination fixed silicone mold

Step 15: Casting gypsum: Mix the gypsum powder with water in a certain proportion to form a gypsum slurry, and pour it from the injection port of the silicone mold to fill it up.

cast gypsum slurry

Step 16: Disassemble the mold: After the gypsum slurry is solidified, the mold can be disassembled and taken out.

replicated plaster model


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