Mold Making
Mold Making Process
Poured Molds
This page is a collection of videos to help acquaint you with the basic mold-making process. Choosing the right release agent is crucial to success. The following videos will recommend a variety of release agents based on the composition of the pattern being molded and the liquid mold rubber being poured. In this video we explain the release and sealers for Polyurethane Mold making.
Silicone molds must be released with a different mold release, one that does not contain silicone oil. Here are some options for mold release when making silicone molds or casting silicone.
Rubber mold making is a vital skill to master if you plan on producing resin parts or any other cast part. The process is fairly simple provided you plan ahead and follow all of the directions. In this tutorial we walk you through the steps to make a simple PlatSil Silicone block mold. This is the most basic of molds, but is also the most widely used for casting our EasyFlo resins. Block molds are ideal for reproducing small, simple parts and flat-backed parts.
To further elaborate on the basic poured mold process, here's a video covering some of the important information on working with Platinum silicone. For this mold, we used very fast setting PlatSil FS-20. FS-20 has a 7-8 minute working time at 70F and a 20-25 minute demold. FS-20 has a low enough mixed viscosity that it doesn't require vacuum degassing for simple molds.
Some patterns are best molded with a brushed-on mold technique. This method is ideal for monuments, portrait busts, and mold applications where the finished mold must be light weight. This method trades material costs for labor costs. Brushed-on molds are more time consuming to make, but use much less silicone or other rubber. In this video we make a simple one piece mold using PlatSil Gel-10. The soft, stretchy properties of Gel-10 are ideal for simple, seamless molds.
This video is a great overview of the molding and casting process with an emphasis on small resin parts. We used PlatSil FS-20 for the mold, 2500 spray release, and EasyFlo 60 casting resin.
Some patterns are best reproduced in a 2 piece mold. A two-piece mold allows access to the entire inside surface as well as molding a part that doesn't have a "flat side" and minimizing undercuts. Typically firmer rubbers, such as Gel-25, 73-20, 73-25, and 80-30, are used for two piece molds as they mate together better without distortion. Avoid very soft rubber such as 71-11 or Gel-10 for two piece molds.
An economical method, similar to the block mold method, is the cavity pour or "poured blanket mold." This is the preferred method for molding larger patterns that would be cost prohibitive to mold in a block. Low viscosity silicones, such as Gel-25, 71-11, 73-25, 73-20, and 73-15 as they are easy to pour and don't always require vacuum degassing.
Concrete Molds
In this tutorial we create a pattern from a tree stump using Gel-25 thickened with Tinthix. The resulting EasyFlo 60 resin part was used to create a Poly 74-20 urethane mold for production concrete casting.
Brushed-on Molds
Brushed-on molds are ideal for applications where a block mold is cost prohibitive or mold weight is an issue. Brushed-on molds are commonly used to reproduce busts, medium sized sculptures, and monument pieces. A brush-on mold trades material cost for labor cost. Brushed-on molds are much cheaper but do require more labor. A brushed-on mold typically requires a third or less of the rubber needed for a block mold. In this tutorial we demonstrate a 1 piece, seamless brush on mold of a skull. Gel-10 thickened with TinThix is great for this type of mold as it is fast setting as well as soft and stretchy.
Thickening Agents
To make a brushed-on mold, the rubber material (such as Gel-10) must be thickened. We offer several thickening agents for brush-on mold making.
PolyFiber
For our Polyurethane rubbers (74 and 75 series), PolyFiber is the preferred thickener. PolyFiber is an inert synthetic fiber that may be added to most oil based materials to create a brushable paste.
TinThix & PlatThix
For silicone molds, TinThix is a chemical thickener that may be added to the mixed silicone to convert it to a brushable paste. PlatThix is another thickener that is specific to Platinum Silicones.
Brushed-on molds do require the added step of a mother-mold or support shell. There are several approaches to making support shells. The lowest cost (but heaviest) option is Hydrocal and hemp. In this tutorial we explain the process of making an TinSil 80-30 two piece mold with a Hydrocal shell. Water based clay is used to establish the parting line to separate the two halves.
A method that combines the best attributes of both a poured mold and a brushed-on mold is the cavity pour or poured blanket mold. This mold is also referred to as a matrix mold. In this tutorial we mold a figurine using PlatSil FS-10 silicone with an EasyFlo 120 mother mold. We thickened the EasyFlo 120 with PolyFiber to create a brushable paste.