Learn how to make a concrete fountain that looks just like sand using Mold Star 16 silicone rubber. We use real sand as the original model and seal it with acrylic spray. Mold Star 16 is then mixed and poured over the sand, curing in 30 minutes to a soft, flexible rubber. The mold can be used to cast glass fiber reinforced concrete (GFRC), or other materials, to create a realistic water feature.