The porosity is somewhat higher than with vibration casting but not as high as with regular gunning. And you get rapid application of the material. Compared with setting forms, pouring, and waiting for the material to set, it's much faster. Spinel forming Martin Marietta and other companies are experimenting with a new technology for castable refractories called spinel forming. The entire mass would have to be eroded away, rather than just the small portion that bonds the material together.
Spinel is a man-made mineral formed by the reaction of the oxides of the aluminum and magnesium.
It is highly refractory and offers excellent corrosion resistance to molten slag. The spinel reaction is catalyzed by the slag as it penetrates the refractory. During the spinel formation, volume expansion occurs, which fills porosity. The substances then freeze and block any remaining porosity. These two mechanisms effectively prevent additional penetration by the slag.