Mold Making 101

Making a mold can be very simple depending on the intricacy of your part.
If you have never made a silicone mold before, begin by making a mold of a simple part. Do not use a valuable original as your part when mold making, unless you are able to run a test to ensure the silicone does not affect your piece.

AeroMarine silicone mold making rubber does not require use of a vacuum.

You will need mixing containers, stirring sticks and a mold box into which to place your pattern while making your mold. Depending on the size of the pattern, 1/2″ of silicone moldmaking rubber is the minimum thickness necessary for your mold. Making it too thick will reduce the flexibility of the mold- too thin will reduce the resistance to tearing.

There are 3 basic types of molds:

  1. BLOCK mold, one piece. The part usually has no negative draft and/or undercuts.
  2. The BLOCK mold, multiple piece, can be made in the same way as the one piece mold. Just cut the mold after it has cured to get the pattern out. Then use blue painter’s tape to keep the two halves of the mold together. Instead of cutting the block mold apart, you can design it to be taken apart. One way is to partly fill the container with the silicone mold making rubber, let it cure, spray silicone mold release, then finish pouring the mold. When it has cured, you can take the mold apart.
  3. The GLOVE mold, brushed onto the pattern, requires the use of our thixotropic catalyst. This is so that the silicone moldmaking rubber doesn’t run off the surface of the pattern. It also builds up much thicker than the regular catalyst. This type mold is widely used in restoration of architectural designs on vintage buildings. The silicone rubber is brushed onto the surface, allowed to cure, then removed. Back in the shop, it is then supported and used as a mold to cast additional parts.

Mold Release

Generally, silicone RTV mold making rubber does not stick to anything, and nothing will stick to it. The exception is that it will stick to itself, other silicones, silica, and glass. If you need to release silicone from itself, use our mold release for silicone. In a pinch, a thin film of petroleum jelly will provide a good release agent.

Silicone RTV mold making rubber may soak into a porous surface and lock in place. This is often the case when making a mold from a wood pattern. To prevent sticking, seal the wood so the silicone can’t soak into it. Krylon Acrylic spray is a good choice. It is compatible with just about any substrate or silicone rubber. Silicone doesn’t stick to Krylon Acrylic. Petroleum jelly can work well as a wood sealant also.

Mixing

For the AM128 series, mix the silicone at a ratio of 100 parts by weight to 10 parts catalyst. A digital gram scale is best for obtaining the correct weight. The AM125 series is mixed 1:1 by volume, not weight. Always mix thoroughly. Since our silicone and catalyst are contrasting colors, it is easy to tell when it is mixed properly. Do not whip air into the mixture by being too vigorous or by using a high speed mechanical mixer.

If you have further questions about making your mold, please call us toll-free 1(800)858-5990.

DO NOT USE LIQUID SILICONE ON HUMANS OR ANIMALS!

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We also sell several accessory products for our silicones:

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