I totally agree with you. I have a similar finsih round my wood burner,
with masterboard for teh register plate, and its all fine.

I cautin that even that mortar (and teh bricks used with it) may degrade
in the rear of open fires where temps 1000C are possible.


Are you sure open fires can produce greater than 1000 degC? They can
certainly get to several hundred degrees (I would guess 400 to 600) but
I am very sceptical that they can get to 1000.

I used to do quite a bit of high temperature chemistry where we started
work at 950 and that was a sight hotter than our fire ever gets.

Andy.