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November 4, 2016
This is a brief overview of the different types of molds you can make with silicone, latex and urethane. This list is by no means complete. Rather, it consists of pictures and a short description of the more common mold types. If you have questions about a particular project, you can always give us a call, toll-free, at AeroMarine Products 877-342-8860.
Types of Silicone Molds:
Pourable silicone makes block molds. Block molds are created by putting an original in a container and pouring the silicone around the piece. They can be one piece or multiple pieces. They can also be a multi part mold, meaning one mold that has multiple cavities for casting.
See All Silicone Mold Products
These purple molds are basic one part, one piece block molds. For the mold on the right the original (a clay witch’s hat) was anchored to the the bottom of a square box and the AM128 Pourable Silicone was poured around it. For the mold on the left (a bat), I made a custom mold box from cardboard and hot glue. Because of the bat’s unique shape, I didn’t want to waste a lot of silicone by putting the original in a square shaped container. The silicone only needs to be a half inch to an inch all around the piece.
These multi-part one piece block molds are made the same way as the previous block mold. The difference is that it has two (or more) original pieces anchored in the mold box.
To create these types of molds, you encase half your original part in a sulfur-free clay inside the mold box. For the mold on the right (rubber duck), you can see the vents at the tip of the duck’s bill. These vents prevent air bubbles from forming in those areas. On the mold on the left (an apple), you can see the sprue for pouring in the casting material. Both molds make use of registration or key marks to help the sides of the mold fit together tightly.
Here’s an example of a mold box with the original piece half encased in clay:
The straw on the bottom right will become the sprue, the other plastic sticks will become vents to prevent air bubbles.
Squish molds are called that because once they are made, you pour a small amount of the casting material into the cavity part of the mold and then place the convex part of the mold on top, essentially squishing the casting material into shape. These molds can be a bit messy until you figure out how much casting material is needed for each cast.
This is a four part block mold of a coffee mug. The bottom image is the mold fully assembled. This was made by encasing 3/4 of the piece in clay pouring silicone, allowing it to cure and then removing the piece from the mold box and clearing another bit of clay off, poring the next area of silicone and so on until I had a four part mold. I will be doing a how-to blog post in the near future on two part and multi part block molds that will have a lot more detail on this process.
This is the brushable silicone glove mold with plaster mother mold that I made for a previous post using AM128 Brushable Silicone. The silicone is brushed on the original piece, usually in 2-3 coats, to create a thin, flexible mold that can be easily pulled off the piece. The mother mold supports the mold while casting. These types of molds are used for pieces that would use a large amount of silicone if done in a block mold, or pieces that are shaped in such a way that making block molds would be difficult. Glove molds are also used when the original is attached to a wall or something and can’t be removed, like decorative trimming or a part of a large facade.
Latex is used when the casting material is concrete or plaster or a type of mock stone material. The reason for this is the latex is much more abrasion resistant than silicone and can stand repeated castings or rough, course material. The latex we carry is only brushable, not pourable.
See All Latex Mold Products
The latex is applied by brushing a thin coat on the original, letting to dry fully and then applying the next coat. You need about 20-25 coats of latex of a strong mold. The mold on the right (tall can) and the bottom picture is made with 25 coats of plain latex and supported with a plaster mother mold. The mold on the left ( a rock) is made with 4 coats of plain latex (the detail or print coats) and then 12 coats of latex mixed 50/50 with black rubber powder, followed by two coats with gauze embedded in the latex. The black rubber powder and gauze make the mold strong and stable enough to not need a mother mold, but they do reduce significantly the ability of the latex to stretch.
Urethane Rubber is used for casting concrete and plaster and other mock stone materials. Like latex, it has a high abrasion resistance and holds up well to repeated castings of rough material. Unlike latex, it is pourable and can be used with pieces where having a poured block mold is desirable. It doesn’t have as much give as silicone because its durometer/shore hardness (75A) is similar to a car tire.
See All Urethane Molding Products
Urethane casting resin is usually used for casting parts, not for making the mold. However, sometimes the part needs to be soft or made of silicone. In that case, you might make your mold out of casting resin. The general rule of mold making is when casting a rigid part, use a soft mold and when casting a soft part, use a rigid mold. I made this mold (a clay heart) so I could cast the part in silicone.
These are some of the basic common mold types frequently used in molding and casting. We will be posting how-to blogs on all of these mold types and many other projects as well!