Hello! Just a quick question- I bought a 50 lb bag of insul cast to fill the 2 inch void before laying the firebrick. However- I was a tiny bit bit short on the insul cast…so it is not exactly level with concrete…I’m short by maybe quarter of an inch or less. Can I just make the difference up with the sand or is it super important that it is level with the concrete?
You’re good, if by “tiny” you mean a half inch or less. There should be enough there to provide the thermal break you need.
So be happy and keep building!