Hi! We'd like to install a gas poured in place concrete firepit on our patio. Does it need to be lined with fire brick, and if so, does the firebrick need to go all the way to the top edge? What I'm trying to avoid is seeing the top edge of the firebrick, and so I'm wondering if it could end an inch or so below the top of the pit so that I could cover it with lava rocks. Thanks for your help!