[deere37]

What type of mortar should I use to build my outdoor fire pit?

 

[Bud Cline]

Refractory mortar.
You can buy it from any brick supplier.

What about the proper brick to use? Why aren't you asking about that?

 

[jomama45]

What you want is a non-water soluable fireclay for exterior projects such as yours. I typically use Heatstop II, or Heatstop 50. Alsey also makes a comparable product. I'm sure there are others depending on region, and you should have little problem finding one at a specific masonry supply house.

 

[tpolk]

thats just the fire box correct?

 

[jomama45]

Correct, just the firebox in this case. On an exterior fireplace though, you want to use it on the throat, reducer, and flues as well, as they're prone to moisture as well.