Since I haven't seen any reference to it, I'm curious if anyone has substituted hardwood lump charcoal for sawdust in their firebrick recipie. I've been experimenting a bit and found it is fairly easy to pulverize/grind down small enough to pass through a window screen. My uneducated theory being it might create more uniformed micro pores in the firebrick, still giving it an insulating value and help to maintain a stronger firebrick. Would appreciate any thoughts on this subject.