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Silicone Casting with Plaster Backing

Posted on Oct 13, 2011 by in Techniques, Updates | 2 comments

Recently I decided to try another casting method.  This time around I used the Platinum Silicone system from Tap Plastics.

I decided to use the blanket casting method since this material is more expensive than some of the other forms.  The blanket method uses up to a third less casting material.

I mixed up a small batch according to the directions and painted it on the part after I glued it to the styrene.  I then thickened up the rest of the material using the thixotropic agent and spread it over the part (the instructions recommend painting the thin mixture on and waiting a while for it to set before adding the thickened coat).  Skipping this step did affect the final quality of the casting, but it didn’t really matter for this part.

After the material hardened I decided to pour a plaster backing to hold the blanket mold when I am casting parts.  I used a plastic package to create the mold and taped it in place on the styrene.


The final step was to mix the plaster and pour it into the prepared mold.

Here is the end result, a blanket mold for producing roofs for small boxcars.  It has good enough detail in the mold to add very fine texture to the cast part.


  1. I may have to give this a try (the TAP Platinum) .. is it that you get many more castings from one of these molds then ‘regular’ RTV?

  2. As far as I know the only differences between the Platinum and the regular RTV silicone is the ease of use. The Platinum is a 1 to 1 mixture that is very thin, hence the thixatropic agent being added for the second step in the casting process. The other nice thing is that the bubbles leach out much easier than the regular RTV silicone, making it so you don’t need to use a vacuum chamber or other special method of mixing. On the down side, it is a bit more expensive. Check out their videos at TAP Plastics.