*See final slide for a SHOPPING LIST for this project
Step 1: Learn the anatomy
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To make building stone walls easier, you can use blocks made from cast concrete and molded to look like real stone (available at any home center). They're flat on the top and bottom so they stack neatly, and some interlock for added strength. Glue them together with masonry adhesive. Choose a block with angled sides, meant to form curves when butted against each other. The optimal size for a fire pit is between 36 and 44 inches inside diameter. That will create enough room for a healthy fire but still keep gatherers close enough to chat.
As an added precaution, the fire pit should be lined with a thick steel ring like the ones used for park campfires. These protect the concrete in the blocks from the heat, which can cause them to dry out and break down prematurely.
A fire pit should sit low to the ground, with walls rising no more than a foot off the ground. But for stability, the base of the wall must be buried below ground in a hole lined with gravel, providing drainage and protecting against frost heaves in winter. the gravel also creates a level base for the stones to rest on. Most concrete blocks are about 4 inches high, so if the first course and a half sit underground, and there are two and a half courses above ground with a cap on top, you'll end up with a foot-high wall—just right for resting your feet on while sitting in an outdoor chair.
MORE: Build an Adirondack Chair
MORE: Want More Wall and Less Fire? Try Building This Fire Pit's Cousin, The Sitting Wall
Step 2: Lay Out the Blocks
Using a 3-inch cold chisel and a brick hammer, score the block on the mark, and continue the score all the way around the block. Place the block on a hard surface (flat rocks or gravel). Hold the chisel in the score line, then hit it with the brick hammer until the block splits.
Clean up jagged edges with the tail of the brick hammer. Place the cut block into the ring.
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Step 3: Mark the Pit Location
Take note of how many stones make up the ring, then remove them and set them aside.
If the blocks you are using are interlocking, remove any tongues on the bottom of the first-course blocks so they will lie flat in the trench. Chip them off with the tail of a brick hammer.
Step 4: Create a Level Trench for the Blocks
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Lay the ring of blocks in the trench to see if all the pieces fit in a circle. If not, dig more to widen the trench. Remove blocks.
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Step 5: Fill the Trench
Always make sure the blocks line up perfectly in the front and back when you lay them out; a difference of 1 inch in the circle's diameter could create a 3-inch gap between blocks.
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Step 6: Lay and Level the First Course
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Lay another block next to the first one. Butt the sides together tightly and line up the front and back edges. Using the first block as a reference, level the second block side to side and front to back.
Lay the rest of the blocks in the trench in this manner until the ring is complete and all the blocks you counted earlier are used. Make sure each block is perfectly leveled and lined up tight with its neighbor before moving on to the next one. (You may have to coax the last block into place with a mallet.) Using a 4-foot level, occasionally check level across the ring.
A small hit with a mallet can make a big adjustment; work slowly and carefully, block by block.
Step 7: Assemble the Walls
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Step 8: Fill the Pit
Insert the iron campfire ring into the circle. Adjust it to sit even with the top of the block wall. Fill any space between the ring and the block wall to the top with gravel.
Work quickly and only in a small area at one time; masonry adhesive sets up quickly.
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Step 9: Cap the Blocks
Lay the stone on a hard surface. Split it by hitting a chisel in the score mark, or by tapping against the stone's edge with the brick hammer until it breaks. Score and split each stone this way, moving around the circle in one direction until you've made a cap that fits together tightly.
If you're using blocks, glue the pieces on top of the wall. If you're using natural stone, combine the dry mortar with enough bonding additive—not water—to make a mix with a peanut-butter consistency.
Wet the wall with some bonding agent. Lay a large mound of mortar on two blocks. With the point of the trowel, make a groove across the mortar. Lay the capstone on top, push it down, then tap it with the rubber mallet to set and level it. Continue to lay the capstones in this manner until the wall is finished. Wait two days before lighting a fire.
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Step 10: Don't stop now! Pick up another DIY project at thisoldhouse.com
...Install a Picket Fence
...Put in a Pond
...Add Drip Irrigation
...Build a Tool Shed
...Make a Trellis
3. STEEL CAMPFIRE RING
The one we used here is from MARKSTAAR
4. 3/4-INCH DRAINAGE GRAVEL
6. MASONRY ADHESIVE
7. READY-MIX MORTAR
(if needed) to cement a natural-stone cap onto the wall. A 40-pound bag is enough.
8. CONCRETE BONDING ADDITIVE
(aka "milk") to make the mortar more flexible.