Tips for Making Silicone Rubber Molds

Silicone rubber is a widely used compound in mold-making and crafting. Movie studio prop makers, taxidermists and artists use the substance regularly. Silicone rubber can produce stunningly realistic molds if used properly. It can also create a huge mess if used incorrectly. Several tricks of the trade can make the process of silicone mold-making easier and less messy.

Mold Box Tips

    The first step to create a silicone rubber mold is to construct a mold box to contain the silicone. Make sure that the box is wide and tall enough to allow for the expansion of the silicone without overflow. The original model that the mold is being formed around should have at least 1/2-inch of clearance on all sides. Secure the original to the bottom of the box with hot glue or a mold-making adhesive so that it will not rise when you add the silicone.

Silicone Mixing Tips

    Most silicone rubber compounds consist of two components -- a base and a catalyst -- that you must mix before pouring into the mold box. Mix the two components by hand for a small mold and with a drill mixer for a large mold. Stir the catalyst and base in their separate containers before mixing them. To avoid trapping air bubbles into the silicone, mix the components slowly in a circular motion instead of beating rapidly. Follow the manufacturer's ratios of catalyst to base for mixing, but keep in mind that the amount of catalyst you add determines the curing time. More catalyst equals faster cure, a little less means a longer cure.

Silicone Pouring Tips

    Most silicone rubber compounds begin to set up after about 20 minutes, so you should work quickly. Allow the silicone to set for a few minutes to let air bubbles rise to the top before pouring it into the mold. Air in the silicone rubber will cause the mold to be weak and may warp or distort the mold. Other tips for reducing bubbles: apply a thin layer of silicone to the box and the model before pouring the full amount; raise the silicone about a foot in the air and pour it slowly; remove air with a vacuum pump; or hold the box at an angle and pour the silicone in on the raised end.

Mold-Setting Tips

    The silicone mold may take anywhere from a few minutes to several hours to set or cure, depending on several factors, including the type of silicone, the size of the mold, the temperature and the humidity. Silicone molds often tear. You can reduce the likelihood of this by reinforcing the mold with cheesecloth, gauze or nylon strips. To do this, pour half or two-thirds of the silicone rubber into the mold, allow it to set until it becomes firm but sticky, lay the cloth strips over the entire mold, then pour the remainder of the silicone and let it finish curing.

Unmolding Tips

    One common tip to make unmolding easier is to spray the original with aerosol cooking spray or to rub it with petroleum jelly before pouring the silicone. Do not attempt to remove the model at the very moment when the silicone is dry to the touch; allow it to set for at least 10 more minutes to ensure curing has completed, especially if the mold is very complex. To unmold the original model, remove the silicone from the mold box and turn it upside down. Pull away the silicone at the edges, then move in to the center. Do not push down on the mold, lift it up and release the model.