Soul Cycle Mothership, a molded fiberglass speaker cabinet for bicycles.

Step 9 Get plastered

Once the rubber mold is complete, you need a rigid outer shell, a "mother mold" to hold the rubber mold when you do your lay up. In my case I chose plaster, because it's cheap, and fast. It's also heavy, so if I were doing a larger shape, I'd think twice about using plaster. But with a shape this size, the plaster Mother Molds are still easy to handle.

As you can see from the second image here, I used baby powder as the mold release. I do not recommend this! It cakes with the moisture from the plaster. I recommend Mold Release wax or Crisco.