In response to customer requests for a "non-fiber filled" thixotropic plastic that will hold a vertical surface, Smooth-On has developed a product we are calling "Shell Shock®". "Shell" because the plastic can be used to form a shell and "shock" in reference to this product's good impact resistance in comparison to other products on the market.
Applications - Shell Shock® is ideal for making fast, lightweight, rigid molds and for creating silicone appliances and effects (use as a replacement for ‘stone molds'). You can also brush a "gel coat" into a rubber mold and back it up with rigid foam, creating a highly detailed, lightweight casting. This product can be brushed onto styrofoam (polystyrol) as an impact resistant coating that can be sanded, primed and painted (minimum 3 coats recommended).
Shell Shock® can also be used to make thin, lightweight, rigid support shells (mother molds) to support brush-on rubber molds. It is mixed 1A:4B by volume and steadily develops thixotropy (becomes thick). Applied in thin sections, the mixture will hold a vertical surface. Like any brush-on material, if you apply too thick it will sag.
Pot life is on the fast side at about 3 minutes which helps with thixotropy, but you have to be aware of your working time. The material will stick to itself, so you can quickly build 3 to 4 layers to a minimum recommended thickness of 3/8" in (1 cm), which is recommended for impact resistance. Time between coats is about 15 minutes depending on mass. Do not disturb the previous layer. Material cures in about 1 hour at room temperature (depending on mass). Gel time and cure time can be reduced with mild heat.
How Is Shell Shock® Different From Plasti-Paste®? Plasti-Paste® is heavily filled with fibers which provide strength and make Plasti-Paste® a good "mother mold / support shell" material. The fibers make Plasti-Paste® thick to the point where you can trowel the material onto surfaces without thickness limitation. Cured Plasti-Paste® exudes an oil that makes it difficult to paint.
Shell Shock® is a different product that chemically thickens and is best applied in thin layers. Applied more like a brush-on rubber (such as Rebound 25®) Shell Shock® wets out nicely on a variety of surfaces. When cured, it is harder and more rigid at Shore 85D (vs. 70D for Plasti-Paste®). Shrinkage on Shell Shock® is very low at .0006 in/in. (cm/cm). You can also sand and paint Shell Shock®.