This type of silicone rubber makes great molds for parts with large undercuts or parts with complex shape that might be difficult to demold from a regular silicon rubber mold created with Alumilite Quick-Set Mold Rubber Kit mold-making kit. Molds made with this high strength 3 RTV rubber are much softer that those made with the quick set silicone, much more flexible and thus have a very high tear strength. Which means that you can easily stretch the mold to take your casting out without tearing or otherwise damaging the mold. And when I say stretch, I really mean it -you can stretch this silicone quite a bit without tearing.
The advantage is that you can reuse your mold many time, extending the life of your mold. The disadvantage of the soft and squishy silicone is that it isn't particularly suitable for two piece molds or molds that require rigidity. The rigidity comes into consideration when you have larger molds and the weight of the resin cast into your mold could push against the sides of your mold and could actually alter/bend the mold resulting in a flawed duplicate.
It is a RTV silicone, or room temperature vulcanization. Which means that it does not require added heat for the mix to turn into silicone rubber. Just mix it and pour it into the mold and leave it alone for 24 hours. This silicone compound has 2 hour open time as opposed to the quick set silicone. But other than that and the softness and tear strength, there isn't much difference from the quick set silicone. The same rules for mixing, creating molds, etc. apply with this product. For additional tips and comments on making molds using Alumilite silicone rubber see my review of the quick set rubber by following the above link.
The high strength 3 RTV silicone rubber is a great product if used for the right type of mold. We've made a number of molds using both types of silicone rubber and had a great success.
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