Tips from the Pros: Making Molds and Castings Like a Pro
How do you replicate a model like this frog corbel? By learning the art of molding and casting. With a little guidance and practice, creating molds and castings can be a fun and satisfying craft.
Abatron offers mold making products and several casting compounds that allow users to create architectural and artistic reproductions with striking detail.
1. Preparing the model. Begin with a clean, dry model. Wipe away any dirt or dust. Once clear, completely coat the model with Abhesive 15-C™, a water-based release agent which will allow the mold to be easily peeled free from the surface of the model. Abhesive 15-C is normally clear, however a blue pigment was added for visibility in this demonstration.
2. Making the mold. To capture the character and detail of the corbel, a flexible mold is created using MasterMold 12-3®, a polyurethane mold making paste. The mold can be reused many times without losing fine details.
Mix equal parts of MasterMold Part A (blue) and Part B (yellow) in a clean bucket. Use separate mixing sticks if portioning less than full containers. Stir thoroughly until the MasterMold is a consistent green color. Apply MasterMold to the model, making sure that all surfaces are completely covered. Add a second layer after the first using a putty knife or spatula, building a thickness up to 3/8 inch. After the second layer is applied, the MasterMold can be smoothed using isopropyl alcohol applied with gloved hands. The mold takes about ten hours to harden at room temperature. Wait until it is tack-free before proceeding to the next step.
3. Making the support mold. A support mold will help the flexible MasterMold retain its shape while creating castings. WoodEpox® is a strong and durable epoxy paste that is easily shaped by hand, making it an excellent choice for creating a reusable support mold.
Begin by wrapping the MasterMold in plastic, and use a hair dryer or heat gun to help the plastic wrap conform to the shape of the mold. This will prevent the WoodEpox from sticking to the mold. Mix equal parts of WoodEpox Part A and Part B, mixing thoroughly until the color is uniform. Apply WoodEpox to the mold in sections, so the support mold can be removed and reassembled. Use plastic wrap to separate the sections. The support mold should be approximately 3/4 of an inch thick. Allow 4 – 6 hours for the WoodEpox to harden. Once hardened, the support mold sections can be removed, and the plastic wrap barrier discarded. A small file or flathead screwdriver can help with separating the sections.
With the support mold removed, slowly peel the MasterMold from the model. Reassemble the support mold, and secure it with tape. Insert the MasterMold into the support mold.
4. Making the castings. Gypsum-1™ is a high quality casting plaster that excels at reproducing fine detail, and a natural choice for the corbel.
To mix a batch of gypsum, begin by adding room temperature water to a clean mixing bucket. Next, measure out the casting compound. The ratio is approximately 3 parts gypsum to 2 parts water by volume.
Slowly stir the gypsum powder into the water, so that no lumps remain in the mixture. Allow the mixture to soak for two minutes before pouring it into the mold.
Use a spray bottle to spray the inside of the MasterMold with water, which will help prevent bubbles from forming as the gypsum is poured. Pour the first batch of gypsum plaster into the mold. Create additional batches as necessary for the project. The gypsum can be shaped and smoothed as it thickens, using a putty-knife or gloved hand. Fiberglass rods can be embedded in the casting as a method for mounting. For best results, allow the gypsum plaster to dry overnight before removing the MasterMold.
5. Removing the casting. Once the casting is fully hardened, it can be removed from the mold. Start by carefully cutting the tape and removing the support mold sections. Next, gently peel the MasterMold away to reveal the finished casting. If any excess gypsum is present, it can be removed with a sculpting tool.
There are many ways to approach the art of molding and casting. Experimenting with different objects and casting compounds will help to refine your technique. If you have any questions about mold making and casting, contact Abatron at 800-445-1754.