If you choose RTV silicone to make silicone casting molds, you're working with one of the best materials available for the manufacturing industry. RTV is shot for "Room Temperature Vulcanizing," meaning once you mix the silicone with other components, you don't have to expose it to extreme heat to get it cured properly.

As you continue your research, you'll find many ways to design and create silicone casting molds, but only one way stands above the others. Going with the block mold, it's a true and tried method to make anything. You only need to pour the silicone inside a box containing your prototype. Once it's appropriately curated into a solid shape, you can remove the whole contraption and pour the casting martial of your choice inside the mold you just created. Rinse and repeat as many times as you need to get as many parts as you like.

Since silicone never sticks to any surface other than other silicone constructs, this is a significant advantage since you're able to cast as many parts as you need without the need to release agents that fill the mold or modify the finished product. Here are the steps you need to follow to get the best silicone casting molds done by your hand:

Building the Block

To build the block, you'll need a big box to cover about half the prototype with silicone. Silicone is very malleable and doesn't rust anything, so you can safely work with scrap cardboard and glue to create a good mold box, make sure to glue all of the seams properly inside and out to keep the silicone from leaking. Before pouring, inspect your prototype one more time and ensure it has no flaws or fingerprints since these are reflected in every finished piece.

To keep the prototype in place, you should use a dab of glue at the bottom while you place it in the center of the box. This will keep the prototype from shifting around or going sideways as the silicone is poured.

Get Rid of Bubbles

To mix up your batch of silicone, follow the manufacturer's instructions. Remember that all silicone mixtures are measured by weight, not volume. You'll notice an air bubble inside the rubber mix as you pour. You need to eliminate these since they are weak points of your build that can make the mold fail for good. You should pour the mixture into a corner first and let it flow across the prototype's surface. Lift the box several times and keep the pouring on a very fine strand. You can use a vacuum chamber if you have one, but if you make a homemade mold, we recommend going for a silicone mix that requires extended curating times.

Make your Cast

With the rubber finally cured, it's time to get rid of the cardboard and peel the rubber off the prototype. We recommend going for a straight middle section cut using tools. Please don't be harsh with them. You can lose the shape of the prototype. If you're working with a noncomplex prototype, you can always turn the mold inside out, depending on the silicone's strength. Now that you have your silicone casting molds, you can begin to create reproductions using urethane resins or any other material. The mold can be washed with water to be reused for future occasions.