FB Board vs vermiculite mix

[Squirt Reynolds]

Can I use a combo of board and vermiculite cement? saw it in a video but they put alum foil between them…
also, do I vapour barrier over the hearth and under board/verm cement?
thanks

[Gulf]

Weep holes? explain pls… I have hearth done…

Here is a link to an example. There are some who drilled the holes after the concrete hearth was poured.