How to Make a Two Part Mold

There are several different ways to make molds. The most common mold types are one-part and two-part molds, with the complex three-part molds used a little less often. One part molds are best suited to flat-backed designs, as they typically require one side of the mold to be completely open at all times. Two part molds are used for most other projects, as they can be taken apart to retrieve a cast object. Three part molds are like two part molds, but have an added inner piece that makes the casting hollow.

Instructions

1

Coat your model with mold release, so that the mold material does not stick to the model.

2

Create an open-top box that will hold your liquid mold material. You can make the box out of pieces of thick cardboard or even wood, although cardboard will be easier to take apart later. Make sure that the box is at least 1/4 inch bigger than the model in all dimensions.

3

Seal the corners, edges and bottom of the box with modeling clay, so that none of the mold material leaks out of the box.

4

Mix together a batch of your mold-making material. Typically, two-part molds are made from either plaster or rubber. Make sure to take the appropriate safety precautions for the material you have chosen.

5

Pour the mold material into the box. Stop pouring once the box is half-filled. Discard the rest of the mixture.

6

Let the mold material sit for several minutes to firm up slightly. When the material is ready, press the model into it so that half of the model has sunken into the material. Let the other half of the model sit above the surface.

7

Let the mold material harden completely. If you have used plaster or rubber, this will set in 12 hours.

8

Coat the top of the mold, which has the model sticking out of it, with mold release. This will make the mold easier to separate later.

9

Make another batch of your mold material. Pour the material into the box, covering the model completely. Fill the box.

10

Let the mold material harden completely. When the material has hardened, take the box apart.

11

Pull each side of the mold apart and remove the model from the inside. Fit the mold back together.

12

Tie the mold together with rubber bands or cording. Carve a hole in the mold, at the seam, that reaches the inside cavity. Use this hole to pour your casting material.