Aldax Moulds and Mouldmaking Supplies

Two Part Silicon Mold Making

How to make a two part silicon mold

This type of silicon mold making is usually called 2 piece block molds as you are totally enclosing your model in silicon, as you do with a normal block mold. However the mold is made in 2 parts for easy release of the model and later the casting.
The model that requires this form of silicon mold making is usually one that has detail on all sides and no flat back.

(1) Select a mould box to contain the Craftsil silicon that you are going to pour around your model. For small pieces this can be a simple plastic container found in any $2 shop or a wood base on which you can build a box wall surround made of Lego blocks, Perspex, mat board or something similar.

(2) Trace a half way line around your model with an Artline pen to show the parting line position of the two halves of the mold. Embed your model up to this line in a non hardening clay such as Plastelina within the mould box. Make sure that the clay is in close contact with the walls of the box and the model to prevent silicon leaking into any intertisces.

(3) Push a few indentations into the Plastelina around your model with the round head of a pencil, or something similar, to make the registration keys that will enable both halves of the mold to fit together exactly.

(4) Press a small plastic tube about as thick as a pencil halfway down into the plastelina at the head or base of the model to act as a feeder channel for the casting medium. Ensure that the tube is in contact with the model.

(5) Coat all surfaces of the box, plastelina and model with a thin layer of wax or petroleum jelly (Vaseline)

(6) Mix the Craftsil silicon mold making rubber with a figure action being careful not to beat any air bubble into the mix. Pour into the mold beginning at the lowest part from as high a position as you can manage. This very thin stream of silicon mold making rubber has the effect of breaking any air bubbles that may be in the mix.

(7) Wait for the Craftsil silicon mold making rubber to cure.

(8) Remove the model and the half poured silicon mold from the mould box. Turn the mold over and remove the plastelina clay.

(9) Reposition the mold half already poured back in the mold box. Seal any cracks between the silicon and the box wall with plastelina clay. Coat all surfaces of the box, silicon and model with wax or Vaseline release.

(10) Now pour the second half of the mold in a similar manner to the first pour and wait for the Craftsil silicon mold making rubber to cure.

(11) Remove both halves of the mold from the mold box and separate. Lift out the model and the tube use to form the pouring channel. Trim any flashing from the mold.

(12) To cast position both halves of the mold together so that the registration nodes are fully engaged and secure together with a rubber band or masking tape.

(13) Pour in a small quantity of casting medium, place a finger over the pouring channel and carefully rotate mould to ensure that all model detail is covered with the medium. Continue pouring the casting medium, tilting the mold occasionally to permit air to escape. Note: Small air channels can be cut into the silicon mould halves if you find there are any undercuts or areas not covered by the medium. When you notice casting medium coming from these channels simply plug with clay and continue pouring.

(14) Open the mold after casting has set but is still a little soft and not completely cured. Remove the casting which will be a faithful reproduction of the original model. Cut off the pouring channel, flashing and any air channels. If trimming is left to do when the model is fully cured you will difficulty in cleaning the casting.

A member of the Alderson Group of Companies, proudly in our 60th year.
Aldax Moulds Site Map