Build a Stone Grill

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The first step is to create a solid foundation for the stone grill.
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The finished stone fireplace/barbecue pit.
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Placement of wire mesh and rebar.
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Note: This illustration does not depict the preferred building up process for the fieldstone work. (It should be one layer at a time.) This illustration is to show how all of the components fit and work together, as if all the stone work were complete and a section was removed to reveal the structure beneath. Only the two bottom layers of wire mesh are shown.
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Wire mesh goes betwenn every layer of concrete block and its adjacent structure. For the sake of clarity, only the bottom layer is depicted in the illustration.
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Note: The “cap” of the structure can be almost any noncombustible material: flagstone (shown), marble, granite, cement, slate or floor tile.

This stone grill uses a 16-inch-by-32-inch drop-in grill unit with a built-in charcoal tray that adjusts up and down to regulate the amount of heat at the cooking surface. The outdoor barbecue grill is a beautiful addition to your outdoor kitchen or the perfect spot for cooking during your backyard barbecue parties. 

We built firebricks around the grill unit and used fire clay mortar or refractory cement to joint them in place. For layout and planning purposes, the nominal size of these bricks is 9 inches by 2 1/2 inches by 4 1/2 inches. If your fire bricks need to be cut, have a masonry supply store do it, or use the old hammer and chisel after scribing the cut line.

To construct the inner core you’ll need common concrete building blocks, sized 12 1/2 inches by 7 1/2 inches by 5 1/2 inches. The cap or top of the structure is entirely up to your discretion. The most common materials used are flagstone, red brick or simply a leveled surface of cement. No matter what material you select, be sure to seal it with a good coat of waterproofing masonry sealer.

To securely tie all these components together, first you will need quarter-inch rebar, placed in a grid pattern with a 6-inch to 9-inch spacing in the concrete portion of the foundation. Second, you’ll need a layer of heavy-gauge wire mesh set between each concrete block layer and between the first layer of block and the foundation. Let the wire extend 6 inches to 9 inches out all the way around the block so that you can weave the wire between the fieldstones and mortar. In some instances it will be necessary to cut the wire to bend it to the shape needed, so have a good pair of wire cutters handy.

Step 1: The Foundation

Dig a hole to a depth of 24 inches. Install posts and 2-by-6 boards (keep the boards level). Add layers of sand and large stones, then add the smaller stones and work in more sand. Note: after the large stones are in the pit, shovel in a layer of sand. To work the sand down into the crevices, hose it down with water. Use just enough water to work the sand into the voids. Keep adding sand until the rocks are just covered.

Add a 2-inch layer of sand and tamp it down. Keep adding and tamping until it’s flush with the bottom of the 2-by-6 forms.

Mix and add post hole concrete. After you have filled the form with 3 inches of concrete mix, lay the quarter-inch rebar horizontally in the concrete before pouring the remaining mix.

Screed (level) the top flat using a 2-by-4. Keep the surface wet for 48 hours, using watersoaked burlap bags.

Step 2: The Inner Core

After the foundation has “cured” for at least 48 hours, wet the top of the foundation and put down a half-layer of mortar in the footprint where the concrete blocks will be placed. Add the wire mesh, working it into the mortar.

Lay the first course of blocks. (Wet the bottom of the blocks in a shallow tray of water before setting them in the mortar. If you don’t, the blocks will siphon the water out of the mortar causing the mortar to be weak and crumbly.) Level the top of the blocks and wet them with fine spray from a hose. Add mortar and wire mesh.

Continue this process until all of the blocks are in place. Add mortar but do not add wire mesh atop the third layer.

Keep the structure wet for 48 hours with the soaked burlap bags.

Step 3: The Firebrick Pit

As always, premoisten the cured layer of mortar and lay down a bed of fire clay mortar on top of the regular mortar. Lay the firebricks and ensure that each brick is level and flush.

Build up the back and side walls one layer at a time. (Unlike conventional bricklaying, you want to keep the grout layer very thin between bricks.) Remember to presoak each brick before installing it. Firebricks are very absorbent.

Leave an eighth-inch space between the brick enclosure and the edges of the installation hanger.

Keep the bricks wetted down for 48 hours.

Step 4: The Outer Fieldstone Layer

Wash all fieldstones until they are free of dust and dirt.

Wet down the slab and block where the bottom layer of stones and mortar will be installed. Moisten as necessary.

Lay the fieldstones and mortar in layers from the bottom up, until the tops of the stones are an inch or so below the top of the firebricks: First, bed all of the stones in a good bed of mortar and fill the inner surfaces as you go. But don’t fuss with the outer exposed surface yet. Keep the mortar about 1 inch in from the final outer layer. Cut and interweave the wire mesh into the mortar and stones as you go.

After the stones and inner layers of mortar are in place, keep the structure wet for 48 hours using burlap bags.

To fill the final outer layer between the stones, use a grout bag and a thin mixture of grout (a little water goes a long way). The grout bag is nothing more than a large cake-decorating bag and is used in a similar way. Just cut a hole the diameter of a standard pencil in the bottom of the bag and fill in the gaps a layer at a time.

Be sure to keep the cavity you’re working on wet (a spray bottle is handy for this). After you fill a cavity, wait about 30 minutes, then smooth and blend the grout into the stone and mortar patches using a damp 1 1/2-inch paintbrush. Try to keep mortar and mortar water off the surfaces of the stones that will be exposed or the stones will have a dull-gray appearance.

Work all of the outer layer of grout up to within 1 inch of the top.

Step 5: The Top

The top can be any material you choose: flagstone, marble, granite, ceramic floor tiles or just plain, leveled concrete. Whatever you choose, make sure it’s flat and level.

Wet down the top of the structure and add a layer of mortar. Lay the top after wetting it. Continue until complete, leveling as you go.

When you’re finished, seal all mortar and cement with a waterproofing masonry sealer.

Wet-bag it for 48 hours.

Install grill unit.

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