Mold Making Process
This page is a collection of videos to help acquaint you with the basic mold-making process. 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.
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.
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.
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.
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.
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
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.