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KitMaker Network

Mold Making and Resin Casting

For simplicities sake, we will use a 1/1 ratio RTV (Room Temperature Vulcanizing) Silicone (Fig 4). Although this type is more expensive by volume than it's 10 to 1 cousin, it is far easier to use and you are less likely to make a mistake with it. The 10 to 1 mix requires a digital scale and has a 24-hour set time. The type we will use here sets in 4 hours. You can start making parts after the set time expires!

Here is a tip that will help you in knowing how much silicone to mix without getting into complex math problems or guessing.
mixing tipWith your part(s) in the mold box, pour enough water into the box to cover the parts being molded by about a half an inch. Pour this amount of water back into an empty mixing cup. Now, in another cup of the same volume, pour half of this water into it until both cups have an even amount in them. This is the amount of each part of your Silicone you will need. Easy huh? In other words, volume of water in mold box equals total volume of silicone for mold. Mark a line on each cup at the water level and empty the water and dry them out really good. Do the same with your mold box. Use a hairdryer to make sure that it is completely dry. This is important.

Now, using the cups that we marked earlier, pour an equal amount of parts A and B silicone into each cup, right up to your marked line (Fig 5). The silicone we are using has one white part (A) and one blue part (B) and when mixed will by a light powder blue in color.

In your separate clean mixing bowl, pour both of these in. Make sure you scrape the sides of the cups really good to get all of the mix. Use your spatula to mix these together in the bowl really well. You want to mix, not whip these as whipping causes air bubbles to form in your silicone.

Scrape the sides repeatedly during this process. When it is thoroughly mixed, you will not see any white streaks (Fig 6).

We are now ready to pour.
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