A fire pit creates a unique space for enjoying fun and safe recreational fires. When determining a location for a fire pit, choose a spot where the ground is relatively flat and even, and at least 25 ft. From your home, garage, shed, or any other fixed, combustible structures in your yard. It is also important that a garden hose or other extinguishing device be accessible at the location.
In this project, two courses of 6″ manhole block are used to create a fire pit with a 26″ interior diameter, ideal for backyard settings within city limits. Manhole blocks are designed specifically to create rounded tunnels and walls and can be purchased from most concrete block manufacturers.
Three 3/4″ gaps have been factored into this design to act as air vents, allowing the natural airflow to stoke the fire. This layout makes the circumference of the second course roughly 1/2″ smaller than the first. A slightly thicker layer of surface-bonding cement is added to the top course to make up the difference.
Surface-bonding cement starts out as a white paste and can be tinted to match or complement any color of capstone. The 8 x 16″ landscape pavers used here are cut at angles to allow 10 pieces to fit around the rim of the fire pit (see illustration on next page).
There are usually heavy restrictions for pit fires within city limits, regarding pit size, seasonal burning, waste burning, and more. Many municipalities also require that you purchase a recreational burning permit issued by an inspector from the fire department. Check with your local building department for restrictions specific to your area.
When not in use or during winter months, you may want to cover the top of the fire pit to prevent damage that may occur in inclement weather.
Note: It is important to allow your fire pit to cure for at least 30 days before building a fire in it. Heat can cause concrete with a high moisture content to greatly expand and contract, causing the material to severely crack or fragment.
Tools & Materials
Hammer or hand maul; Tuck-point trowel; Tape measure; Circular saw with an; Shovel abrasive masonry blade; Hand tamp; Eye & ear protection; Wheelbarrow or mixing box; 2 x 4; Wire brush; 2 x 2 wooden stakes (2); Mason’s string; Mason’s trowel; Spray paint; Spray bottle; Compactable gravel; 60-lb. concrete (12); Jointing tool; Square-end trowel; Sheet plastic; 6″ manhole blocks; 1/4″ wood spacers (3); Chalk; Refractory mortar; Surface-bonding cement; Mortar tinting agent; 1/2″ plywood; 8 x 16″ landscape pavers (10).
StepI: Excavate the Site
1. Use a hammer or a hand maul to drive a wooden stake into the centerpoint of the planned fire pit location. Then drive a temporary stake into the ground 10 1/2″ from the center stake.
2. Tie a mason’s string to the center stake-the string should be just long enough to reach the temporary stake. Hold or tie a can of spray paint to the end of the string. Pull the string taut and spray paint a circle on the ground.
3. Remove the temporary stake and drive it into the ground 22 1/2″ from the center stake. Pull the string taut, and spray a second circle on the ground.
4. Strip away the grass between the two circles and dig a trench 10″ deep.
5. Fill the base of the trench with 2″ of compactable gravel. Tamp the gravel thoroughly.
StepII: Pour the Footing
1. Mix concrete in a wheelbarrow or mixing box and shovel it into the trench until the concrete reaches ground level. Work the concrete with a shovel to remove any air pockets.
2. Screed the surface of the concrete by dragging a short 2 x 4 along the top of the natural form. Add concrete to any low areas and screed the surface again. Finish the concrete with a trowel.
3. When the concrete is hard to the touch, cover it with a sheet of plastic and let it cure for 2 to 3 days. Remove the plastic and let the concrete cure for an additional week.
4. Fill center of the concrete circle with compactable gravel.
StepIII: Lay the First Course
1. When the concrete has sufficiently cured, layout the first course of 6″ manhole blocks with three 3/4″ gaps for air vents using 3/4″ wood spacers.
2. Mark the internal and external circumference of the first course on the footing with chalk, and remove the blocks. Take note of any low or high spots on the footing, remembering that low spots can be leveled out with extra mortar at the base.
3. Mix a batch of refractory mortar and lightly mist the footing area with water. Throw a bed of mortar on the misted area, covering only the area inside the reference lines.
4. Set a manhole block into the bed of mortar, centering it on the footing and the chalk reference lines. Press the block into the mortar until the joint is approximately 3/8″ thick. Place the second block directly against the first block with no spacing between the blocks and press it in place until the tops of the blocks are flush. Use a scrap of 2 x 4 to help you position the tops of the blocks evenly along the first course.
5. Continue laying the blocks, making sure the spaces for the three air vents are correctly positioned with the 3/4″ wood scraps. Do not allow the wood spacers to become set in the mortar.
6. Continue laying blocks until the first course is set. Remove any excess mortar with a trowel and finish the joints with a jointing tool.
StepIV: Lay the Second Course
Dry-lay the second course of blocks over the first, offsetting the layout of the joints between the blocks. Note: Because of the air vents in the first course, the second course is slightly smaller in diameter. When laying the second course, line up the internal edges of the blocks, leaving a slight lip along the outer edge.
StepV: Apply Surface-bonding Cement
1. Mix a small batch of surface-bonding cement according to the manufacturer’s instructions. Add a mortar tinting agent, if desired.
2. Mist the blocks of the fire pit with water. Apply the surfacebonding cement to the exterior of the fire pit walls using a square-end trowel. Make up the difference in diameter between the two courses with a thicker coating of surface-bonding cement on the second course. To even out the cement, angle the trowel slightly and make broad upward strokes. Keep the top of the fire pit clear of surface-bonding cement to ensure the cap will bond to the wall properly.
3. Use a tuck-point trowel to layer the surface-bonding cement inside the edges of the air vents. Do not cover the air vents completely with surface-bonding cement.
4. Use a wet trowel to smooth the surface to create the texture of your choice. Rinse the trowel frequently, keeping it clean and wet.
StepVI: Install the Capstones
1. Make a capstone template from 1/2″ plywood, following the illustration (above right). Use the template to mark ten 8 x 16″ landscape pavers to the capstone dimensions.
2. Cut the pavers to size using a circular saw with an abrasive masonry blade and a cold chisel. When cutting brick with a masonry blade, make several shallow passes, and always wear ear and eye protection.
3. Mist the top of the fire pit with water. Mix a batch of mortar and fill in any block hollows, then throw a bed of
mortar along the top of the second course.
4. Butter the leading edge of each capstone, and position it on the mortar bed so the front edges overhang the interior diameter of the manhole block roughly by 1/8″. Adjust the capstones as you work so the joints are 3/8″-thick and evenly overhang the exterior edge of the pit. Also make sure the entire layer is even and level. Tool the joints as you work.
5. Use a jointing tool to smooth mortar joints within 30 minutes. Cut away any excess mortar pressed from the joints with a trowel. When the mortar is set, but not too hard, brush away excess mortar from the faces of the capstones with a wire brush.
6. Allow the fire pit to cure for 30 days before its first use.