Refractory or regular mortar for chimney base

[SteveP]

I ran out of Heatstop 50 refractory mortar and need about 5 pounds to finish the chimney base. This stuff is expensive and I can only find it in 50 pound bags locally. Do I need refractory mortar for the chimney base? Both arches have refractory, but since I already have regular mortar at the house, I thought about using it. Will it get hot enough to affect regular mortar?