Bricking\vermiculite 3x12 lighting

[canuck]

We just bought a newer used arch to replace are old one, It was just bricked all the way back to the stack. The arch that we are replacing was bricked, then had vermiculite and sand on top of the bricks, The sand in most places came level to the cross members of the arch. I am confused now about how to re-brick the new arch,any suggestions on the proper way to re-brick?

[maple flats]

If raised flue, fill the entire area behind the firebox up to enough with Vermiculite that when you lay a layer of brick flat you are within 1/2-1/4" of the top rails. This should go back until you drop down to just 1 layer for the last 6-8" before the stack. Buy the vermiculite from a commercial greenhouse supply in like 4 or 6 CF bags. Large or small curd either is good.

[canuck]

how do we brick the slope directly behind the grates?
Thanks