Use a brush to clean debris from the surface of the previous layer. Overlap the layers of stone, leaving three or four random gaps between stones in every course. The gaps allow the fire to draw air into itself. We dry-stacked the stone. They may get out of alignment, but realignment is easy. We learned something the hard way: put gravel into the center of the fire pit after you've stacked a couple of courses. Then spread it evenly when you're finished. We shoveled the gravel into the pit after it was completed and found lifting the gravel that high was unnecessary work.