I am wondering if anyone out there knows if you can use your broken insulating firebricks to make or improve refractory cement? They are so brittle and crumble easily and I was wondering if make them into powder then make your own refractory cement or improve existing cement?

use them as grog? https://en.wikipedia.org/wiki/Grog_(clay)

I don't know as I use the pieces till they pretty much turn to sand---a bowl of insulative firebrick pieces makes a nice surface to use a torch on as you can stick pieces in it to hold them in place for the torch.

Welcome aboard Frostyforge, glad to have you. If you'll put your general location in the header you might be surprised how many of the Iforge gang live within visiting distance. 

The characteristic that makes soft fire brick crumble with thermal cycling doesn't go away unless you crush it into powder. Anything you use it as grog in will want to crumble as the "grog" degrades.

Frosty The Lucky.

I have an idea that requires about 6 soft insulating firebricks but I'm not ready to shell out the cash for new bricks (not yet, anyway) as it may not work.

If any are rebuilding gas forges and have a surplus of used soft fire brick (4.5x9x1 or 2 inch or there about) and are willing to donate the bricks, I'd be willing to pay the delivery cost (within reason) to Missouri.

Not looking for perfect bricks, but at least two (or enough partials to make two) need to be able to span 6-7 inches on their own to form a top.

Thanks.

Grog generally uses dime sized pieces of hard refractories suck as flue tiles or hard fire bricks. 

Ground soft firebrick would make a nice insulating filler.