Laid down the fiber, one-inch 8lb. density. I had a bunch of replacement IFBs for an electic kiln so I decided to place them around the edges. Had enough to go two rows on each side and they seemed to fit together well so I used them up.
I cut the center flue bricks out of K26 IFBs and set them in place. I had to order some kiln cement so I'll cement them in place when that arrives.
I plan on filling in the rest with an even layer of crushed IFB and will eventually cover the top with some 16 gauge sheet metal.