How to Make a Two-Part Mold Using Mold-Star 30

Create a two-part mold using Mold-Star 30.

Supplies

Model or object of which negative mold will be created

Block of non-hardening clay to make base for model

Bolt or nut to impress alignment keys in the base

Cardboard to construct mold box around base

Hot glue to seal the mold box

Mold-Star 30 to create the mold

2 Spatulas to mix the Mold-Star

Step 1: Create the Clay Base

The goal of this step is to create a place holder for the bottom half of the mold out of clay. This way, you can pour the Mold-Star silicone on top of the clay and the model, creating the top half of the mold.

Start with a block of non-hardening clay, and create a cavity in the block to fit your model.
Build up the clay around the model to where you want the seam of your mold to be. The seam is normally halfway up the model.
Ensure the clay is as smooth as shown in the picture. If the clay base ends up with irregular bumps, it produces mold halves that are difficult to de-mold.

Step 2: Add Keys to the Base

Use a bolt or nut to add impressions into the clay base. This helps both parts of the mold to come together in the right orientation. Keep in mind that the more textured the key is and the more there are, the more difficult the de-molding process will be.

Step 3: Build the Mold Box

Hot glue four pieces of cardboard together around the base, and further seal each edge with hot glue. This ensures that no silicon seeps through.

Step 4: Mixing and Pouring

The ratio between Parts A and B of the Mold-Star is just 1:1 by volume or weight. Pre-mix each part individually before you pour, using separate spatulas for each.
Combine Part A and Part B and mix thoroughly with both spatulas. Scrape the sides and bottom until there are no streaks. If you do not mix enough, you will find cured swirls at the top of your mold.
Spray mold release onto everything before pouring the mixture to help with the de-molding process. Let the mold release sit for 5 minutes before pouring.
Slowly pour the silicone into the mold box in one location and let it find its own natural level, which dramatically helps with bubbles.
Leave everything to cure for 6 hours.

Step 5: Remove the Top Half of the Mold

After the mold is cured, remove the mold box from around the mold and set aside the cardboard for now.
Carefully peel the clay from the model and mold. Do not remove the model from the top half of the mold.

Step 6: Making the Bottom Half of the Mold

Rebuild the mold box around the top half of the mold, with the impressions in your new mold facing up.
Fill any abnormal caps with extra clay to limit leakage. Keep a hot glue gun ready to fill any seams that may leak silicone.
Spray mold release onto everything again and let sit for 5 minutes.
Pour the silicone mixture into the mold box as done with the top half of the mold.
Allow everything to cure for another 6 hours.