When you're setting stone in mortar, make sure that you don't let the mortar cover the front of the stone you've already established. Take a trowel and just cut it off so your stonework looks clean. Also, be sure you're not creating perfectly straight horizontal or vertical lines with your stones. To avoid continuous joints, use stones of different length and width as you work. Using a jointer and an inexpensive brush, dig out the joints and brush the excess away for a more rustic appearance. It is a good idea to joint as you go along so that the mortar doesn't get too hard. Remember that, for the inside of the fire pit, you want to use firebricks — which are longer, thicker and wider than regular brick. They are also heat resistant. You'll place the firebricks standing tall one beside the other, all the way around the fire pit (Images 1 and 2). The soldier course helps with the circular design. Make sure you put mortar on the bottom and sides of the bricks and fill the joints.