RTV Silicone Mold Making

mold making supplies

Before you get started on your project, here is a list of supplies you will need. We will discuss some of them more in depth in the tutorial.

-Your plug (the part you want to replicate)
-Something to cast in whether it is a plastic cup, a box you make out of wood, a water bottle cut to size, etc.
-Glue- hot glue applied with a glue gun works well
Clay (modeling clay)
Two part silicone
-Large mixing cup
-Paint paddle or stir stick
-Small scale if you need to measure your silicone by weight
Mold release or petroleum jelly (not essential but a good idea to use)
-Knife, razor blade or scalpel
-Safety supplies including gloves

siliconemold3

If you are looking to make a silicone mold, you obviously have something you want to replicate.  In this demonstration we are using a child’s ‘Little People’ pirate.

You will want to have some sort of container to make the mold in.  We used a small measuring cup.  Another option is to make a mold box out of plywood or corregated plastic. There are many materials you can use but make sure it is not porous. To construct the box you will want it to be 1/4″ to 1/2″ larger on each side of your plug (the part you are replicating).

If you are making a box, first measure your plug, then add the extra inches to the base.

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Next, you will want to use glue to anchor your prototype to the center of the base of your container. Hot glue guns work well for this.  That way you can easily remove your plug/figurine when you are done. You could also use screws if you want.  Use clay to fill in any gaps where you connected your plug to the base.

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If you are building a box, you can then cut the sides to size. It doesn’t matter how tall you make the sides as long as it is tall enough for you to cover your plug.  Glue or screw together all the pieces making sure there are no leaks. Don’t put a top on the box. Other options for a mold container are a clear mailing tube, plexiglass or a water bottle. Whatever you choose, make sure it has a smooth surface.

Before you start working with the silicone, make sure you are working in a well ventilated area.  Use gloves to protect your hands and either tyvek coveralls or an apron to protect your clothes.

RTV sillicone mold making

RTV silicone comes in two parts. The mixing instructions vary by the type and brand you buy. Some are an easy one to one ratio and some are by weight.  If the silicone you buy is by weight, use a small scale to measure out the two parts. The one pictured above is a 10:1 ratio by weight or volume. Figure out how much silicone you need to cover your plug before starting. You don’t want to mix too little!

Isokote

It is not imperative to use mold release but it is a good idea. You can use a release like ISOKote, Ease Release 2300 or even petroleum jelly. It makes the mold easier to work with.

Measure out the two parts of silicone.  Some people will measure Part A in one cup and Part B in another cup.  Then they will combine both into one large cup.

mixing silicone demo2

Mix really well with a paint paddle or stir sticks. Mixing well is crucial. Make sure you scrape the sides and bottom until you have a uniform color. There should be no streaks when you are done. You do not want any uncured spots in the end. You can roll around the mixing cup to try to get air bubbles out before you pour it into you mold container.

pouring silicone demo

 

pouring silicone demo2

Pour a thin stream of silicone into the mold container on one side.  Let the silicone work itself around your plug. Tilt your mold box/container from side to side to work out air bubbles.  They should flow to the top. The cure time time varies by the silicone you buy.

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This particular silicone took 16 hours at room temperature.

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For this particular demonstration, the side of the plastic cup was cut to release the mold. If you made a mold box you can tear away the sides or unscrew the wood pieces, depending on the material you used. This makes it easy to get your silicone mold out.

cutting RTV silicone mold

Using an exacto knife or scalpel, make a zig zag cut in the silicone.  Don’t cut all the way through on your first cut.  Slowly cut the silicone away from your plug.  You do not want to rip or tear the mold.

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Your plug should easily pop out.

finished silicone mold

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If you cut the mold correctly, it should go back together nicely. You can fit it back into your mold box or plastic container to prepare it for casting. Once that is done, you are ready to replicate your plug.

We will be putting up another blog post shortly to show you how to cast. We will also be posting a YouTube video of the process shown above. Keep checking back!

For more information, go to www.fiberglasswarehouse.com .

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