Casting polyurethane resin pieces from rtv molds

Ok so now we got our RTV mold that we can use to cast resin pieces.

There are a lot of different type of resins you can use for casting, but the one we like to use is Quickcast from Silpak. This resin sets in 10-15 minutes which is a good thing. (Trust us on this, you don’t want to wait hours for this stuff to set, especially if you have to make 500 pieces.)

Measure out the specified quantities of liquid A and liquid B. It will tell you on the side of the container what the mix ratio is. Mix them together and stir well. (Make sure you read the instructions! If you get it wrong, the resin won’t harden and you’ll have this lovely goopy mess to clean out of your mold.)

Pour the resin into the RTV mold.

As the resin solidifies, it will go from clear to milky white.

When the piece is solid, you can pull it from the mold. Test by pulling on the sides of the RTV mold and see if they pull away cleanly. (This is why we like flexible RTV molds and not cement molds.)

The resin piece can be pulled while it is still soft and bent as needed. Just remember that if you wait too long, the piece will be too hard to bend. It may take a couple practice tries to get the timing right.

And here is the finished piece! You can see how Judy bent it in a bunch of places to make it into the shape she needed. For consistency, she made a block out of sculpey to bend the resin piece over. (That’s that little white block you see.)

For finishing the resin piece, you can sand it down with sandpaper and then paint it with acrylic paints or spray paint. In this case, Judy first gold leafed the pieces and will go back and cover them with another coat of gold paint later. (These pieces were used on her Trinity Blood Catherina costume.)

The last thing you need to know is that molds will degrade with usage. Eventually you’ll find that the pieces you’re pulling from the mold aren’t as nice as when you started. Once a mold degrades too much, we just chuck it and make a new one. You can get anywhere from 10-20 pulls depending on the piece. You can use a mold release to extend the life of the mold, but stick with a spray-on mold release.

Ok, that’s it! Now you can go forth and cast! Woo!

We wrote up a FAQ to hopefully answer any more questions people have that we didn’t answer here. If we missed something, feel free to email us and ask!