In preparation for my BK Princess inserts, I have to repair my hearth. 3 of the 4 bluestone were so lose that I can lift them right up. After removing the blue stones, I see that they were being supported/secured on a few yellow bricks with mortars. Can I use regular red bricks and mortars from HD/Lowes or must I use refractory bricks and mortars? I posed the question to 2 of my local mason retailers. 1 said yes and 1 said no. I asked my friend who's a GC and he said no. I asked my stove installation contractor and he said yes. I asked my local fire inspector and he doesn't know. Would appreciate any much feedbacks. Thank you.