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Mold Making and Resin Casting

When deciding on the amount of resin to use, you can rely on the same water principle that was discussed in the silicone section. However, as mentioned before, water and resin do not mix! Any moisture left in your mold will ruin your casting. So I use a different approach. Because I do a lot of casting of many different products, I have a multitude of molds on hand. So I usually try to mix up enough resin to fill multiple molds, or at least keep another large mold near by so if you have extra resin from the part you are making, you can just pour it into the "reserve" mold so it doesn't go to waste. I make many parts this way in multiple pours. That is, if I have any excess resin from the primary part I am making, it goes right into a reserve mold of another part, even over the top of cured resin. It is possible that new resin over cured resin may not form as strong a bond, but I have only had this problem once, where a part separated at two different pour lines. Unless you are dealing with a structural part, you don't need to worry about this. I stress though, if the part needs to be a structural member, do it in one pour.

OK, we have our molds ready to go from earlier. Let's mix some resin. Earlier I suggested the use of latex gloves because that is what the manufacturers recommend. I personally do not use them. I have had my hands covered (accidentally of course) in resin and have had no ill effects from it. I caution you though. If you do get resin on your bare skin, use the wiping rag you have handy to take care of it, finish the pour, then get to a sink and wash the affected skin immediately with soap and water. I should also mention that the resin I use has no odor or noxious fumes while setting so no mask system is needed. Most urethane resins are this way. Polyester and epoxy resins are another subject and we will not cover the hazards of such here.

Decide on the amount of resin needed to fill your molds and pour half that amount of part A and half of part B into separate mixing cups. It is VERY important that these amounts are identical (Fig 28).

Then combine these parts into one cup and mix thoroughly with a mixing stick. You should see no swirls of either part when mixed properly, that is, it will be a nice amber color when mixed (Fig 29). The cups will all be thrown away as once the resin cures, they are unusable. I do use both sides of a mixing stick though, so I get 2 mixes out of one stick.