I've made over 30 injectable molds with the hard plasters, so I have some experience in this endevor. i've used ultra cal, hydrastone and settled on superstone. Superstone is pretty new, it has fibers in the plaster for exra strength and is the same price as the other stuff. I vibrate my plaster the same way, works great, but paint a print coat of plaster on the baits with a small brush before pouring the rest of the plaster in the mold, that eliminatesthe bubbles. One coat of elmers and water is all I use to seal.