Before you begin digging your footing, select the location for the fire pit. Use a hammer to drive a pole into the ground to mark the center of your fire pit. The fire pit for this demonstration will be five feet in diameter. To mark off the area, measure 2-1/2 feet of string to use as a radius, anchor the string to the center point and use marking paint to create a five foot circle using the string as a radius. (If you were building a fire pit that is 6 feet in diameter, then you would need to use 3 feet of string to draw your circle.) To determine the inside line of your circle, reduce your measurement by 14 inches and use your marking paint to draw your interior line. Once your markings are complete, you're ready to start digging. Dig down eight inches between the inner and outer lines you made earlier. You must dig down before you build up so the walls of your fire pit will have a strong base that won't sink into the soil.
Mix your concrete with water until you have a thick consistency like peanut butter. Make sure you are wearing your safety mask to protect your lungs from the dust. Once you have mixed the concrete, pour the mixture into the circular hole you created and use a trowel to smooth the surface (Image 1). Use a grinder with a diamond blade to cut pieces of rebar to lengths of approximately three each. Bend the rebar and place it in your concrete, then use a hammer to get the rebar a few inches below the surface to strengthen your footing (Image 2).
Before you begin setting your stone, create a separate pile for your capstones. You will use them later. Capstones are the finishing stones that will form the top of your exterior wall. Be sure to save the stones with the flattest surface in your capstone pile. Mix your mortar, including one shovel-full of lime for increased strength. Add the lime dry. Once the lime is mixed well with the premix, then add water and continue mixing until you achieve a smooth consistency. Using your string tied to the center pole, measure out 32 inches to use as your guide when you are laying the perimeter stones. Use mortar to set the stones in place and use your guide frequently to make sure the perimeter stones are placed at equal distance from the center point of your fire pit.
Use your string guide again, and measure 14 inches from the outer circle to the inner circle. Locate the highest point of the inner circle and place your first brick. Make sure it's level, then use that height to level all of the following bricks you lay around the interior circle. Remember to keep measuring, checking to make sure the inner circle is always 14 inches from the outer circle.
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.
An easy way to build a support system for the grill is to use your firebrick. Just pull two firebricks forward from the rest of the firebrick. If you think of the shape as a clock, you'll pull bricks forward at 12, 3, 6 and 9 o'clock — then you can rest your grill on the supports to cook or remove it if you just want to sit around the fire.
You should dry-set four or five of your larger capstones on opposite sides of the fire pit before using mortar. Use your long level (four feet or more) to make sure your capstones are just about level. When you start to mortar, make sure you mortar the guiding capstones first (Image 1). It's important to get them as level as possible, both individually and in relation to the other capstones (Image 2). If you're building the grill, remember to cut the interior capstones in such a way as to allow the grill to be placed and removed easily (Image 3). When you are capping, it's always a good idea to use a short level. That way you can check the level across and also from front to back. Once all of the capstones have been mortared in place finish jointing, remove any excess mortar along the fire pit. To create the finished surface on the top of your fire pit, fill the joints with mortar then brush them clean (Image 4).
To give the fire pit a more substantial presence in the yard, add flagstone stepping-stones around the fire pit. Simply place the flagstone around the exterior of your fire pit, packing soil beneath the flagstone to prevent them from moving. To create the masterful finish you desire, pour half-inch pea gravel into the center of your fire pit. You have the option of setting logs or coal on the pea gravel. With that, your outdoor fire pit and grill is complete.