Silicone Casting

Since these molds are designed to be filled right up to the top with silicone, you need to make sure things are level before casting. I do this by taking a sheet of wood (melamine works great because its plastic surface is easy to clean) and shimming its corners with paper or tongue depressors until it is level in both the X and Y axes.

Next, you'll need to mix equal parts of your silicone A and B by weight. This mold requires 8.5 fl oz of liquid silicone. Since you're going to lose a bit in the cup when you pour, it's good to have some excess, so mix together 5 fl oz of part A and 5 fl oz of part B to bring the combined total to 10 fl oz.

Put on your nitrile gloves and place your cup on to your digital scale, tare the scale to cancel out the weight of your cup, and pour in your silicone. When you've got the right amount, mix it thoroughly with a stir stick or tongue depressor. Stir for at least a minute, making sure to scrape the sides and bottom of the cup to ensure there are not unmixed areas that could end up as uncured goo in your finished mold.

Pour your silicone into your mold halves slowly, in a thin stream, holding the cup about 6" or more above the mold. This thin stream will help get bubbles that were introduced to the liquid while stirring pop before landing in your casting. Keep pouring until the liquid is level with the lip of your prints.

Allow the silicone to cure. This will vary between products, so refer to your datasheet on that. The one I'm using, MoldMax 15, takes 4 hours to cure at room temp. If you're casting in a hot place, that time will be a bit shorter, and it will be the opposite in a cold environment.

After it's cured, you can pull the mold. I designed these ones with pull tabs to make the process easier. However, silicone is a forgiving material, and if you design a mold without pull tabs, you should be able to use a tongue depressor or blunt-edged thin metal tool like a stiff-blade putty knife to pry the casting out of the mold. 

This guide was first published on Feb 20, 2018. It was last updated on Sep 05, 2018. This page (Silicone Casting) was last updated on Feb 20, 2018.