Hey William, what ya planning on building, j-tube or batch-box?
Yeah, as Glenn mentioned, best not to use IFB in the firebox's heavy wear areas where it will be subjected to cleaning tools and stuffing wood in the stove etc. IFB is very insulating, light in weight, and low density.
Wood fired heat is relied upon as my only heating source. I spared no expense in building my indoor RMH, needing a system built tough for as close to zero chance of breaking down in mid heating season as possible. A system that would give Methuselah a run for his money, so to speak:)
Construction is standard fire brick (9.0 x 4.5 x 2.5, dense, aka 7 lbs. per brick) for the Peter van den Berg batch-box combustion unit (6" system size) along with some standard fire brick "splits", cut to form the firebox's Vee floor.
The heat riser is constructed solely from 2600° F. IFB, stacked on edge for a 2.5" riser wall thickness, all mortared together (1:1, fire clay to masons sand). Totally self supporting, very rugged, long lasting, and quick to build. No added insulation is needed, the IFB do a fine job all by themselves.
The brick layout I followed is similar to that pictured on Peter van den Berg's site, with the exception of the Vee floor brick arrangement:
http://batchrocket.eu/en/designs#brick1
I used the ceramic wool blanket to insulate the batch-box combustion unit. Then everything is encased in regular brick, the non-holed kind of solid brick many homes and commercial buildings are "faced" with. The whole thing, thermal mass bench and all, is encased in that brick, kind of "Russian stove" style.