Riser and Fire brick question

I'm trying to work out materials for my RMH J tube riser.

1.    What are the options besides fire bricks?

2.    Could I use this for the riser (and wrap in a high density ceramic fibre blanket)
By which I mean make a cob mix up with it . . . .

 -  Code 1010 White St Thomas Stoneware Clay.
 -  A high temperature throwing body suitable for reduction or oxidation. Good handling properties and resilience make it very suitable for production potters. Good for large dishes and particularly attractive under reduction.
 -  Recommended firing range 1160-1300C / Cone 4 to 11
 -  Indicative texture 5 (Smooth 1-Coarse 10)
 -  Indicative % Total Contraction @ 1200C 11%* Shrinkage: 1200C 11%



3.  Is this fire brick okay?  It is £5.80 each!!!

- Insulating Fire Bricks
- Max Operating Temperature range 1260 – 1350 degrees.
- Dense Operating Temperature range 1260 – 1500 degrees
- 9″ X 4.5″ X 3″ – 230X114X76 mm
- Made from high purity refractory clays, with graduated additions of alumina for the higher temperature products and a carefully graded organic filler, which burns out during manufacture to give a uniform, controlled pore structure. - These bricks give good thermal insulation, enabling the use of thin walled construction. Due to their light weight and low thermal conductivity, absorb minimal heat, giving significant energy savings. The very low iron and alkali flux content confers good refractoriness and the high alumina content contributes to their stability in reducing atmosphere.

Regarding using the stoneware clay for riser. How thin can you extrude it to keep it stable? If it's not going to be less than half firebrick (32 mm) then it's rather not worth - you will create continuous structure without expansion joints and it will crack. Of course it doesn't preclude its further use as the riser lining, but eventually the cracks will cause pieces to crumble off. Thin dense firebricks laid on stretcher with a wrap (or IFBs on the outside) will work better and much longer.

For using insulating firebricks in the wood fire flame path I recommend reading this short thread:
https://permies.com/t/389334/rebuild-replacing-IFB

On the other hand, if you don't care about decades of trouble free performance and like to rebuild things then there is a wide array of materials to experiment with.