This wood-fired, outdoor masonry stove can be used four ways: for baking, grilling, cooking and smoking. Whatever your cooking needs, this outdoor oven can do it, thanks to interchangeable grill grates and griddle surfaces. If you want to grill steaks or fish, use the grill grate. If you want to bake bread, slide on the steel griddle, stack some bricks on top to retain heat and add the door to hold in the heat. If you want to use the stove top, just slide the metal plate (or griddle) over the top of the firebox.
The oven has a thick insulation layer of lightweight perlite/cement between the firebox and surrounding concrete block, and we included a removable door. This design holds the heat in the firebox where it’s needed. (Perlite is the porous white stuff often found in potting soils. You can buy this mined mineral product at garden centers.)
You can build the outdoor oven in stages, a few hours at a time. (You’ll need a few days between some steps.) Check local building codes before you start building. The oven is made from materials you can buy at local hardware or building stores. You may be able to find some of the materials at a salvage yard, too. Even if you only use it to bake bread, you can save enough money in one year to more than pay for the $300 cost. Ideally, the stove is built to a comfortable height with concrete countertop space on each side, plus a roof to protect against the elements. We covered the concrete blocks with tile, primarily for aesthetic reasons, but you could apply stucco over the blocks, or just paint them. Having an outdoor sink and storage space nearby is also convenient.
Another key design element is the firebox size — not too small, not too large, but just right. Properly sized fireboxes heat up quickly, have improved combustion, produce less smoke and stay hotter longer. We measured cookie sheets, bread pans, medium and large roasting pans, canners and baking dishes to arrive at our optimal firebox size of 13 inches wide by 28 inches deep by 13½ inches high.
Our outdoor oven requires a fire in the firebox for about 45 minutes to one hour to reach a baking temperature of 450 to 500 degrees Fahrenheit. Or, if you want to grill, you can start in less than half an hour. The stove requires almost no maintenance. There’s no need to clean grease out of the oven because it will simply burn away next time you use it.
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Materials
53 medium-duty firebricks (2½ in. by 4½ in. by 9 in.)
28 concrete blocks (4 in. by 8 in. by 16 in.)
12 concrete half block 4 in. by 8 in. by 8 in.
4 80-lb. bags cement
1 80-lb. bag cement mortar for tile and block
2 wheelbarrows of sand
2 wheelbarrows of gravel
1 2-gal. bucket fine sand
3 13-lb. bags perlite
1 quarter-inch steel lintel (1½ in. by 14¾ in. by 18 in.)
1 small bag concrete pigment
10 ft. of 6-in. stovepipe
1 tube silicone
38 sq. ft. tile (for four sides)
4 to 5 lbs. grout
1 steel griddle (¼ in. by 15 in. by 18 in.)
1 steel grill grate (15 in. by 18 in.)
1 grate (fridge/oven rack) (13 in. by 18 in. max)
36 in. stove gasket (optional seal)
1 metal insulated door with handles/vent
Total cost: $300. This price assumes you do all the work, and utilize recycled grates and stovepipe from yard sales. Everything new would cost $400-$500.
Step 2: Pick a Site
Choosing the right location for your stove is important for convenience and optimizing its use. Putting it near your indoor kitchen will save lots of steps, but consider the direction of prevailing breezes so smoke doesn’t blow toward your house or outdoor dining area. Face the stove door downwind for optimum results. Also, consider privacy, ambience, adequate drainage, and space for wood and fire starting supplies. Optional considerations could include adequate space for a cover (highly recommended), dining space, additional countertops and any other extras you might want.
Step 3: Set the Foundation
After you’ve selected and cleared your site, build a foundation to support the stove. A low-cost rubble trench foundation is recommended for most situations. The specifics will vary due to climate and soil conditions, but a rubble trench is usually 18 to 24 inches deep and filled with gravel, or gravel and stone. If you’re building the stove in a harsh climate with strong freeze-thaw cycles, add a French drain (a small valley filled with stones) to remove moisture. Raise the building site if necessary to avoid moisture problems.
For our rubble trench foundation, we used chunks of recycled broken concrete, also known as “urbancrete,” instead of stone. Concrete chunks from flatwork slabs, such as sidewalks and driveways, work best. They can be recycled and stacked like stone. Stack these up in layers to the top of the trench. Fill gaps with gravel and then tamp solid.On top of the rubble trench, pour a 3½ -inch by 40-inch by 40-inch concrete pad. This will create a strong, level foundation for your stove. Make sure the pad is level and square. (We poured an entire concrete floor for our outdoor kitchen instead of a just a small leveling pad, but the concept is the same.)
Step 4: Build the Concrete-Block Base
The next step is to build a concrete-block base two courses high with ladder reinforcement (a wire mesh designed to add strength and prevent cracking) between each course. Use 4-inch by 8-inch by 16-inch blocks with a few half blocks as needed. No cuts are required in the base if you follow the plans. Be sure to lay the block as perfectly plumb, straight and square as possible. Allow to dry for two days or so to gain strength.
Fill the base with gravel or a mixture of sand and gravel. Fill the base with two 6-inch layers, tamping each layer gently. Go easy on the tamping so as not to strain the concrete block joints. All you’re trying to do is settle the materials.Complete the base by pouring a 4-inch layer of lightweight cement level with the top of the block base. This creates a strong, insulated layer under your firebox. Perlite is perfect for high-heat applications such as this. (According to the Perlite Institute, perlite is used to make gas fireplace logs.) Perlite mix for base: 1 1/3 bags cement, 13 pounds perlite and water. This cement-rich mix is strong enough to support the heavy load of firebricks and countertop, yet also insulate the firebox from the mass below. Let the concrete cure for four to five days.
Step 5: Lay Down the Firebrick
After about five days, the lightweight concrete should have cured sufficiently and you can begin building the firebox with firebrick. Place a half-inch layer of fine, clean sand on top of the lightweight cement. We screened our own sand (one two-gallon bucket) through fine mesh. Use a straight edge to make it as level as possible. Precise leveling is a critical step that determines the accuracy of the firebox.
The first layer of firebrick creates the hearth. Standard firebrick size is 2½ inches by 4½ inches by 9 inches. The front row of firebricks is perpendicular to the other firebricks and extends 2 inches beyond the concrete block (see photo, above). This makes it easy to sweep coals and ashes into a bucket. We added half-inch concrete board shims under the front edge for stability, where sand would fall away.
All firebricks are placed without mortar so they are free to expand and contract. The placement technique involves carefully sliding each firebrick straight down — one against the other — into place to avoid gaps. After the first course is set, use the end of your hammer handle to tap on any high spots until all firebricks are flush with each other.
Measure the front of the base and find the center, which should be about 20 inches from either side. Start the first layer of firebricks by placing two bricks on either side of the center of the base, making sure that the brick hang over the front about 2 inches. (The first layer of firebricks should be 8½ inches from the back and 11 inches from the side of the base — if you follow the diagram instead of the photos.)
I made a last-minute decision to lengthen the firebox by 4½ inches (one firebrick width). In hindsight, this probably wasn’t the best choice because now we have minimal insulation on the back of the firebox. My advice is to use one less row of firebricks than shown in the photos. So the hearth will have 14 firebricks, not 16 as shown in the photos. The drawing shows the recommended approach, and the materials list below is based on this smaller firebox.
Continue stacking firebricks for the sides of the firebox. These are stacked on edge as shown above. The firebox is easy to build and the bricks can be stacked in about one hour. You may encounter a few firebricks that are not perfectly sized. Buy a few extra so you have spares. It’s important to keep everything plumb, square and level, and all firebricks flush with each other, with no gaps.
Step 6: Put in the Steel Shelf
If you don’t have experience welding and cutting metal, you might want to have a machine shop make the metal pieces for you. Otherwise, you’ll need a welder and a cutting torch for this step.
At this point, you can put the steel shelf (lintel for chimney) in place. It measures 14¾ inches by 18 inches by 1½ inches (the sides are 1½ inches high) and is made of quarter-inch steel. The most important measurement is the inside width, which for our shelf was 14¼ inches. This allows firebricks to fit perfectly without being cut. The steel parts are joined with six spot welds: three per side, on the bottom so they don’t interfere with placing the firebrick. With a cutting torch, cut a 6-inch diameter hole in the center for the stovepipe. With the steel shelf in place, flush with each side, set the remaining firebricks in place to form the chimney base.
Step 7: Build the Upper Half of the Concrete Block
To form the outside of the oven, set the remaining two courses of concrete blocks (with ladder reinforcement between courses), being careful not to bump the firebricks. Around the firebox opening (where the concrete blocks meet the firebricks), leave an eighth-inch space to allow for expansion and contraction. We stacked CEBs (compressed earth blocks) temporarily inside the firebox to keep them in place. Bricks would work just as well. Let the block dry for two to three days.You’ll need a right angle grinder or wet saw to cut a few concrete blocks around the front of the firebox. Both tools will do the job, but my preference is a right angle grinder because of its low cost, ease of use and versatility. (You also might be able to rent one for this project.) We used it to cut CEBs for the wall behind our kitchen, steel reinforcement, tile and concrete blocks. We even used it to grind and sand our wood poles for the cover and to grind the edges of our concrete countertops and griddle. It paid for itself on this one job.
Step 8: Pour Lightweight Cement
You can now fill the area between the firebox and concrete block with lightweight cement. We used a higher ratio of perlite for this to maximize insulation around the firebox (compressive strength is of less concern on this part). Perlite mix for upper half: two bags cement and slightly less than 26 pounds perlite. (We saved a tiny amount for the insulated door and chimney base.) Allow to dry a few days before proceeding.
Step 9: Build the Countertop
The next step is to build the countertop. We chose poured-in-place concrete countertops for their strength, and resistance to heat and moisture damage. For instance, we don’t have to worry if a storm blows some rain into the kitchen. Strength is important so we can clamp a grain grinder to the countertop, an important issue if you’re going to bake healthy breads. Our countertop design holds the firebricks in place. Although hot pads are typically used, we don’t have to worry about setting down hot pans hurriedly or otherwise be overly concerned about damaging the surface. Tile is also very practical, but we used it on the sides of the stove and wanted something different on top. Stone is another good choice, but too expensive for our budget.
We were looking for an inexpensive way to make concrete countertops and came up with a pretty good solution at a fraction of the cost of custom made countertops — about $20 instead of $2,000. (This cost is for 12½ lineal feet of 25½-inch countertops.)We used 100 percent scrap materials for forming, about a half bag of cement, some quarter-inch rebar, and baling wire, sand, gravel and iron oxide pigment. Forms consisted of leftover eighth-inch cement board and scrap wood. We placed rebar in a grid pattern and then poured concrete on top. Create an eighth-inch space between chimney and countertop with a removable shim to allow for expansion and contraction. As the concrete set up, we used an edging tool to round the edges. Pigment was troweled on the surface as the concrete started to set up. It only takes a tiny amount of pigment sprinkled here and there to create a beautiful color. After the forms were stripped in three days and the edges touched up, we applied a “paint” of iron oxide mixed with water to the edges. You might want to splurge an extra $10 to $20 and add pigment to the entire mix to make integrally colored concrete.
Step 10: Make the Chimney
Building the chimney is straightforward. There is a damper within easy reach to control air flow and save firewood; open it up when starting fires, and close it down when baking so all the heat doesn’t shoot up the chimney. A cap on top of the stovepipe keeps out rain and snow, and a boot (or collar), along with some silicone, seals the connection on the roof. The stovepipe is in sections to facilitate removal and cleaning. The gap between the stovepipe and chimney base is filled with lightweight cement.
Step 11: Add Tile
Tile is an excellent finish material that withstands a lot of abuse but also looks beautiful. You can get creative with tile, and it’s a good value. To decide on the color, bring samples home from the store and see what looks best. You might want to choose tile in advance and make slight adjustments to the stove size for a perfect fit. You can tweak sizes of concrete block joints to get tile to fit perfectly and reduce the amount of tile cutting. You can also apply stucco to the concrete blocks or simply paint them.
To apply tile, first scrape the block wall clean of concrete residue. Use a drop cloth to protect the floor. Line up the tile to determine even spacing. Draw a level line around the stove as a guideline for the first row. (We started at the base on the front.) Mix a bucket of mortar, brush water on the back of each tile (or soak tile in water) and trowel on about three-eighths inch of mortar with a pointed trowel. Taper the edges, and lightly press each tile into place. Check for alignment in each direction. A few light taps of your trowel handle will seat the tile firmly in place. Check again for plumb, level, even spacing and to ensure the tile is in the same plane as the stove. It helps to change your angle of view and sight lengthwise along the surface periodically.Allow the tile to set up a bit and then work grout into the joints with a rubber grout float. Do one section at a time, smoothing the joints and cleaning the surfaces in stages with a sponge. Squeeze out extra moisture from the sponge so the joints aren’t weakened by too much water getting into the grout. Remember to allow an eighth-inch gap between tile and firebricks for expansion and contraction.
Step 12: Add a Smoker
All you need to turn your outdoor oven into a smoker is a grill grate (or typical oven grate) about (midheight) in the firebox. Simply drill four holes in the firebrick lining the firebox, insert steel pins in holes and add the shelf. You can also suspend a drip pan from the grate with wire. An oven thermometer is useful for making sure the temperature is right throughout the smoking process.
Step 13: Grill Grate and Griddle
The outdoor oven uses a grill grate and a griddle of the same size to enable multiple cooking functions. Simply replace one with the other depending on how you’re cooking. For frying, baking or boiling, use the quarter-inch steel griddle. For baking, stack bricks or concrete blocks on top of the griddle to store heat. Another nice feature is adding a grate on the bottom of the firebox to raise pans slightly to improve air circulation and reduce burning. Another optional energy-saving feature is to add a stove gasket to seal the griddle and prevent air leaks.
Step 14: Put on the Door
The door is the key feature needed for baking. We built a 2-inch-thick insulated door of sixteenth-inch steel filled with perlite. This is another firewood saving feature. The front piece of the door forms a lip that hangs over the firebox opening about half an inch to help reduce air leaks. The large wooden handle doesn’t get too hot to touch and enables the door to be installed and removed with one hand. There are no hinges; the door wedges into place. We added an adjustable vent to control airflow and spray painted the door with heat paint. Based on our experience, a 1¾ inch hole in the door seems to be the perfect size. If you’d prefer a simpler method for building the door, make a thick hardwood door with a piece of metal on the inside, allowing about a quarter-inch air gap between wood and metal. You could rabbet the edges for a tighter seal. Also, a thermometer built into the door would be a nice feature.
Step 15: Fire It Up!
Wait a few days for the tile to cure before firing up the stove for the first time. We started with a small fire and gradually, one fire per day, built increasingly larger fires in order to drive out any remaining moisture.
The Fastest Way to Start a Fire:
Place two 2-inch-diameter pieces of firewood in each side of the firebox. Add crumpled newspaper between and place dry sticks on top of the newspaper across the 2-inch pieces of firewood. Add more twigs (up to the size of your little finger) on top in a crisscross pattern. Avoid placing too much wood at first to allow good airflow. Have everything ready before lighting the fire: small split kindling and 1- to 2-inch pieces of firewood or charcoal.Open the damper and the vent hole in the door. A lit candle can help start the fire quickly. Add kindling after three to four minutes when twigs are solidly ablaze. Add larger pieces after about 5 minutes. Wait 5 minutes and close both the damper and vent holes half way.
For tips on how to cook with your new outdoor oven, visit this article on the Mother Earth News website.
Participated in the
Humana Health by Design Contest
CliffL15 made it!