How to make a silicone block mould

Hi Everyone,

I think everyone will be able to make some use of these techniques in their mould making work. Let me know if you require any additional assistance. Today we are going to look at how to create a simple Silicone Block Mould. This is one of the simplest ways to make a silicone mould.

Silicone Block Mould

How to Make Silicone Block Moulds

Block moulds are amongst the easiest silicone moulds to make. However they use quite a lot of material, so in some cases they are not economic. This is probably the most widely used technique for making moulds in our mould making factory.

A block mould is made by pouring silicone over and around the model forming a solid, but flexible block of silicone rubber. The block mould method is also used to make ceramic moulds of plaster and non flexible moulds of epoxy and polyester resins for special use.

A one-piece mould is the easiest to make and probably the most widely used. A one-piece mould can be made of any  model that does not have severe undercuts and has a flat back

A multi-piece mould has to be made of any model that requires both the front and the back of the model to be reproduced. This type of mould can be used to reproduce any undercuts or difficult release areas.

A third type of block mould can be made where ther model is totally encased in silicone and a seam is cut down one side of the finished mould to enable the model to be released. This method is widely used by manufacturing jewelers.

How to make one-piece silicone block moulds.

Step 1. Adhere your model to a suitable base. We usually use a piece of scrap melamine covered MDF board, offcuts from the kitchen cabinet manufacturing industry.

Step 2. If the model is porous, seal it with an acrylic sealer such as CraftSeal.

Step 3. Make an enclosure around the model using wood, metal or plastic.

Step 4. Roll pieces of oil based clay such as Plastelina into strips and press into all areas of the enclosure where silicone could leak.

Step 5. Apply a release agent to the model and all parts of the base and walls of the enclosure.

Step 6. Mix the silicone thoroughly with the catalyst in the manufacturers recommended proportions. Pour the silicone slowly onto the lowest part of the future mould and allow it to slowly rise around the model thus reducing air entrapment. Hold the mixing container as high as possible when pouring so that the silicone descends in a  very thin stream. This method effectively breaks any air bubbles that may be present in the silicone.

Pouring the Silicone

Step 7.Allow to cure for the required period and then remove from the enclosure.

No doubt this will be your most commonly used block mould so try it out to-day.


How to make a two-piece silicone block mould.

Multi-piece moulds must be made with care to reduce unsightly seam lines in the finished product. There is no limit to the number of parts that can be incorporated in a multi-piece mould, if required to enable easy release of undercuts and other protruding areas that would be difficult to release.

Step 1. Mark a parting line, usually around the middle of the model, with a Texta pen.

Step 2. Place the model on a suitable base board and press into  some oil based clay such as Plastelina up to the marked parting line on the model.

Step 3. Level the clay around the model and make an enclosure around the clayed up model. Level and press clay up to the walls of the enclosure to prevent leakage of the silicone. Shape half of  a pouring spout into the clay usually at the base of the model.

Step 4. To enable accurate mating of the two finished halves of the mould make some “keys” or pressed indentations in the clay surrounding the model, with a small spoon or round head of a pencil. Apply mould release.

Step 5. Mix and , carefully remove the mould half with the model still partially enclosed while removing any adhering clay.

Step 7. Replace the half mould and model back into the enclosure and clay up any potential leaks.

Step 8. Apply mould release to the walls of the enclosure, silicone and model.

Step 9. Pour the silicone to make the second half of the mould and allow to cure and then remove the finished mould ready to cast.

How to make a silicone block mould with a cut seam.

For the sake of this exercise we will assume we are making a mould of a small toy soldier but it could equally be an engagement ring.

Step 1.Select the most suitable area of the model to use as the casting point. In the case of a toy soldier it would be the base of the figure. On a suitable base board place a conical clay pouring spout shape and position the base of the soldier firmly upon it.

Step 2. Build an wood bounding box or similar around the figurine to contain the poured silicone.

Step 3. Seal all openings with oil based clay.

Step 4. Apply mould release and then pour silicone to cover the model to a height 15mm above the top of the figurine.

Step 5. Allow the mould to cure and remove from the enclosure surrounding it.

Step 6. With a scalpel or similar start cutting a seam through to the surface of the model on the side of the figurine that you had  preselected as most suitable for the seam line to be. Do not attempt to cut right through to the model in one stroke rather make a series of small cuts about 10mm in size. This will leave a jagged look to the opening but this does not matter in the slightest as it will assist in registering the cut sides of the opening you are making. Take care when you are close to the surface of the model and endeavour to make a clean cut for the seam line.

Step 7. When cutting is complete, peel the opening wide and remove the model.

Rubber bands may be used to keep the opening closed during casting. A seam line of this type properly cut should be almost invisible on a casting.


Have fun!

Best wishes,

Stan Alderson

Aldax Enterprises Pty Ltd



Silicone Block moulds


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