Build Inner Fire Brick Wall
Level each brick, then fill the gaps in between with wet mortar, scraping away any excess (images 1 and 2). Make sure to measure the inside and outside edges of the wall periodically to maintain the wall's thickness and circular shape.
Continue to raise both the bricks (against the inside circle) and the stones (against the outside circle), filling in any gaps in between with stones and mortar as the wall grows (image 3). Staggering the seams of the stones and bricks makes the structure more stable and gives it a nicer look. Use a jointer to remove excess mortar from between the stones (image 4).
To finish the structure lay a cap of pre-selected flat fieldstones on top of the wall.
Add about an inch layer of mortar and then begin laying the stones, making sure the tops create a flat, even surface along the entire circumference. Add more mortar between these capstones (image 5) to complete the fire pit.