How to Make a Silicone Block Mold

Introduction: How to Make a Silicone Block Mold

About: I make cool things! at least that's what I tell myself

Making a block mold (or one part mold as some call it) is a simple and easy way to make multiples of a part, prop, figure or whatever you can think of. Its also the easiest way to get into the the mold making process, opening the door to more complicated brush on mods, 2 part molds all the way up to the matrix mold.

I hope this instructable is helpful to anyone wondering how to get started with mold making.


You will need.

- Your part to be molded

- Tin or Plat cure silicone (I will be using Mold Max 20 by smooth on)

- Kitchen scale - Xacto knife

- Straight edge

- Foam core or cardboard (for your mold box)

- Hot glue and hot glue gun

- Mixing Cups and mixing sticks

- Silicon pigment (optional)

- nitrile gloves

Step 1: Size Your Mold Box

First thing we want to do is size up our mold box. This is the container that will be holding both our part and our silicone, giving our mold its shape.

Using our part to be molded, a straight edge and Xacto we are going to cut out the base for our mold box as well and our mold walls.

You want the mold walls to be around a half inch taller then the highest point of your part and you want your base to have enough space to give you between a quarter and a half inch of space between the walls and your part.

Step 2: Making the Mold Box & Sealing the Seams

First, using hot glue, glue your part to the base of the mold box. AVOID using CA glue as this can inhibit the ability for your silicone to cure, leaving you with an expensive mess.

Next, we want to take some sulfur free clay, such as monster clay or most water clay and close off the seam between our part and the base. This will stop the silicone from leaking under our part giving us a cleaner mold in the end. As well, the reason for sulfur free clay is, once again we don't want to cause any cure inhibition.

Once that is sealed up we can construct our mold walls. Hot glue the walls to the base about a quarter to a half inch form the from your part, once that is done, use the hot glue to seal up any gaps that you may have on your mold walls, there is nothing worse then pouring a mold only to have your silicone leak out leaving you with an expensive puddle.

Step 3: Mixing and Pouring the Silicone.

For this mold I am using MoldMax 20 by smooth on, this is a Tin cure silicone that mixes 100 parts A to 10 Parts B so be sure to have a kitchen scale handy. Once the 2 parts are added to the mixing container, I add a small amount of silicone pigment (Sil Pig) to tint the silicone. This is optional, however, I find that it helps by giving you a visual to let you know your silicone is mixed well. Then you just mix everything up with a stir stick until you have an even colour all the way through .

Once you are done mixing, poor your silicone in one section of the mold from about 18 inches above and allow the silicone to flood the mold box. By pouring high and in one location this will reduce the introduction of air bubbles. Once you are done pouring, tap the sides of your mold box to help any trapped air move to the surface of the mold and away from you part. This will help with a cleaner mold in the end

Step 4: Demolding!

The final step is to demold your part.

Tear the mold box apart, there is no need for it anymore. Next carefully pull the mold from the part. you might next to use an Xacto to do some minor clean up, but really, that's it! You have successfully made a silicone block mold, ready for casting!

I hope this has helped you if you were ever stumped on how to start mold making.

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