Larry - is this thought train taking you round to my idea of using plain bricks and epoxying them together ?
The key idea behind my suggestion is that the brick(why not choose an "engineering" brick - high temp fired) having aged, it is now stable, cheap, and comes in a suitable modular size to create a variety of shapes.
It also crucially cuts down the amount of epoxy required, avoids cavities, no need for vibrating tables.
You can pre-drill holes for inserts that can be potted in place afterwards, and by jigging in whatever accuracy you need.
You could also drill through to add reinforcing rods under tension if that was appropriate.
Larger table areas could be built by laminating paving slabs, again with epoxy.
You could even build a torsion box on the same principle !
Regards
John
It's like doing jigsaw puzzles in the dark.
Enjoy today's problems, for tomorrow's may be worse.