Silicone Rubber for Resin Molds
Silicon rubber could have been created just for making resin molds—it is so well-suited as a material for making resin molds. Mold-making goes all the way back in history to ancient Egypt and China where they used sand, wax, glue, animal fat, gypsum, alginate, metal, plastic, antlers, and even gelatin to make their molds. Today, however, most resin crafters making custom molds choose one of the flexible rubber materials, latex, polysulfides, polyurethanes, or silicone rubbers, because of the traits they have in common: they can replicate fine detail; removal from mold (demolding) is easy due to their flexibility; they can be used for multiple castings; and durable enough to withstand multiple castings.
Silicon rubber has an inert nature that gives it good release properties as well as good chemical resistance, and high temperature resistance. Though relatively expensive compared to like materials, silicone rubber’s positive attributes make it worth the cost. Silicone rubber comes in two popular formulations that are both useful for casting polyurethane, epoxy and polyester resins, waxes, all gypsum products, and low-temperature metals.
Tin-cure (condensation) silicone is comprised of two component materials which cure (vulcanize) at room temperature (RTV) that when combined make a flexible, high tear-strength rubber. Tin-cured silicones can be poured onto models or they can be made brushable by adding a thixotropic agent. Though tin cure (condensation) silicone has a shorter shelf life than does its platinum cure (addition) counterpart and it tends to shrink somewhat, it is more cost effective and suitable for most resin molds.
Platinum cure silicon rubber, also known as addition cure silicone, is a two-component high tear strength and flexible mold compound. It is widely prized for its extremely low shrinkage and high physical properties. These rubbers are chemically sensitive to latex, sulfur, and certain other materials. Platinum cure silicones can also be used to cast prosthetics for special effects makeup and medical purposes, as well as for making molds that will be used for food if certified as food compliant. Silicone molds by ResinObsession are made from a superior platinum cure silicon rubber.
Because the silicone rubber formulations have only a 1-1/2 to 2 hour of air time before they start to cure or harden, it is important to complete as much of the preparations for the project before combining the two separate components. Also be sure to read all of the manufacturer’s instructions: it is vital for a successful project that the components are thoroughly mixed in correct ratios, leaving enough time to form and if necessary pour your mold before the silicone begins to cure. Always read the MSDS sheet, as the manufacturer may have changed things and this is their only way to tell you.
