Barrel Ovens
A comprehensive, step-by-step system for building improved barrel ovens Written by PCVs Elizabeth Wood and Zeeshan Malik (AG NICA 45) Edited by Bayardo Etienne, APCD Nicaragua, November 2009
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Table of Contents Chapter 1: Introduction ...............................................................................................- 5 What is an improved barrel oven?..............................................................................- 5 Where did the idea come from? ..................................................................................- 5 How and why does it work? ........................................................................................- 5 Why is it a good project for anyone? ..........................................................................- 5 What are the products that can be processed in this oven? ........................................- 5 General Information ...................................................................................................- 6 Materials .....................................................................................................................- 6 Tools ............................................................................................................................- 6 Chapter 2: Preparation ................................................................................................- 7 Step 1—Preparing the Barrel .....................................................................................- 7 Step 2—Preparation of the mud and base ..................................................................- 9 Chapter 3: Building ....................................................................................................- 11 Building Phase 1: The first three layers, ramps, and mounting the barrel ..............- 11 -
Construction of the ramps.....................................................................................- 13 Mounting and securing the barrel ............................................ ......................................................................... ............................. - 15 Building Phase 2—The Middle Layers .....................................................................- 18 Building Phase 3:The Top ........................................................................................- 20 Chapter 4: Finishing Techniques ..............................................................................- 26 Chapter 5: Using your oven .......................................................................................- 27 The First Burn ...........................................................................................................- 27 Chapter 6: General Maintenance and Trouble Shooting Shoo ting........................................- 28 General Maintenance................................................................................................- 28 Trouble Shooting.......................................................................................................- 28 References ....................................................................................................................- 29 Acknowledgements .....................................................................................................- 29 -
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Chapter 1: Introduction What is an improved barrel oven?
The improved barrel oven is exactly what the name implies: a more efficient, woodburning oven that uses convection to heat and cook. Where did the idea come from?
Barrel ovens have been in and around Nicaragua for some years, but have recently taken root within Peace Corps thanks mainly to the NICA 45, Agriculture group. This group took the original idea after an IST session about this technology and made significant improvements in the design, reduced the costs, and made the overall design more sustainable. How and why does it work?
This oven is a double chamber oven; the outer chamber is where the fire rests and where the hot air circulates. The inner chamber is the inside of the barrel, where you will be cooking. The oven works because of the heat retention provided by the bricks. In this model, the fire is used to heat the bricks, which retain the heat and radiate it towards the central barrel. The circular design of the brick house allows the hot air to continually circulate, thus keeping the temperature high enough to cook for long periods of time with relatively little wood consumption. Why is it a good project for anyone?
Simply stated, this oven uses less wood, and heats up faster, and maintains heat longer than other models. Anyone can do this fun project no matter what sector you are in, as most people in Nicaragua use wood-burning ovens. This model will give people the opportunity to bake independently; as opposed to older models in which you need one person to gather wood and maintain the fire, another to prepare whatever you are cooking, and yet another to do the actual cooking; with the barrel oven, one person can light the fire, prepare the food, and bake all independently. What are the products that can be processed in this oven?
This oven can be used for preparing household food but also to bake/toast different products for selling and generate income. Some of the products baked on these ovens are: Corn biscuits (rosquillas/hojaldras), corn bread (cosa de hornos), bread and cakes. Also the oven can be used to bake turkey, chickens and other meats, but also to toast coffee and cereals, and it even can be used to burn pottery in small scale.
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General Information • • •
Cost: $60 Time to build: 4-5 hours (usually broken apart over 2 days) Space needed: minimum 45inch x 60inch, flat area
Materials •
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250 bricks 1 metal barrel (55 gallons barrel) 2 bars of 3/8¨ rebar (1 for the grill (parilla) and another for the construction of the oven) Two 4 inch door hinges 2 lbs solder for welding 4 sacks of sifted white dirt (tierra blanca de hornilla) (used for ovens/stoves) 2 sacks of horse manure 1 bucket of water mixed with 1 pound of guácimo bark (Guasuma ulmifolia) (only needed if the mud you are using is not as sticky as you would like)
Tools • • • •
machete level (nivel) measuring tape with metric measurements (cinta métrica) hacksaw (cierra para cortar hierro)
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Chapter 2: Preparation Step 1 —Preparing the Barrel Once you have purchased your barrel, you will need to take it to a welder to get some work done on it. Materials to take to welder:
55 gallon barrel 2 pounds of solder Two 4inch Hinges 1 3/8’’ rebar Instructions for welding the barrel: •
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Cut a half circle from the top of the barrel (it is best if the removed section has the screw-top opening in the middle because it can be used later as a latch to open the door.) – This will form the opening door of the oven. Smooth with a file. Using a soldering gun, attach two 4¨ hinges and a handle to the front of the removed section. Hinges Screw-Top Handle
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If desired, solder a spare piece of metal in the shape of to the inside of the screw-top to function as an interior latch to secure the oven.door. Inside the barrel, solder 4, 8cm by 1cm by 1cm metal rectangles to support the rack. They should be placed at the widest part of the barrel, even with the bottom of the opening and approximately 8cm from the front and 20cm from the back. (Make sure that the supports are even and allow the rack to sit levelly.)
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Once you are done with your barrel, it should look like this, with a handle on top to open and close the door. This oven also has an extra piece of ¼’’ rebar welded to the outside edge of the door. This is a technique that helps to seal the oven door and eliminate heat-loss, though it is not necessary or included in the directions, it can be done.
Instructions for forming the rack: • •
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Cut 3, 82cm pieces of 3/8¨ rebar and 14, 56cm pieces of 3/8¨ rebar. Solder the 56cm pieces to the 82cm pieces approximately 5cm apart in accordance to the subsequent illustration. Placed with the 56cm pieces up, this will form the rack of the oven. If you are looking to save costs, you can use a ¼’’ rebar to form the rack.
The rack:
The finished rack inside of the barrel.
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Step 2 —Preparation of the mud and base You will need to mix the dirt and horse manure to form your mud, and then use this mud to build your base and eventually your entire oven. Materials needed to make the mud:
4 sacks of white soil 2 sacks of horse manure 1 bucket of Guasimo bark (Guasuma Ulmifolia), soaked in water (only needed if your mud is not as sticky as you would like) Instructions for making the mud: •
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Locate a 2 meter x 2 meter clean space, and empty your sacks of dirt and horse manure in this space. Using a shovel, mix the dirt and horse manure together, turning the pile several times, once to the right, then again to the left, much like the way you would mix a bag of cement with sand. The best way to mix the mud is with your feet. Put on your mud boots and dance around on top of the mud. Mash it with your feet, and then use the shovel to make a new pile, and again mash the mixture down with your feet. Mix together with enough water so that the mixture is wet but not dripping. Continue mixing thoroughly until of even consistency.
Mixing the mud with your feet is the best way to get great mud
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Instructions for making the base: •
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Your base can be customized to the site. The base can be made free standing, using an existing wall or as part of a kitchen wall. When positioning your base remember to leave space for access in the front and back of the oven. The minimum size of the base is the size of the oven, but a recommended size is approximately 60 inches by 45 inches (about 5 bricks long and 4 ½ bricks wide). Once you have chosen your area, level the ground as much as possible and mark off the lines where the walls will be placed. It should be made with square angles. Wet the ground along your lines and place a layer of mud. Then position the bricks to make walls using the mud as mortar. Stagger and lock each level of bricks for strength and durability. Continue layering bricks until the base is three levels high. You should now have a rectangular well. Fill the well with nearby rocks, stones, sand and dirt, packing well, until you reach the bottom of the topmost layer of brick. Level it off. Now put down a layer of mud and fill in the top with bricks to make a flat table. (Just mud can be used instead of brick to fill in the top, but it is more durable with brick.) Use white dirt to coat the outside of the bricks for a more finished look and let dry overnight.
The finished base/table should look similar to this. You will build a well with four sides of bricks; fill it in with rocks and filler, then lay approximately 26 bricks on the top. The end product looks like a cube made entirely out of bricks, but really it’s just the outside layer that is bricks, inside is pure filler. It is important that your final surface be flat and level to build your oven properly.
Make sure to always “lock” your bricks when building. As the picture illustrates, you want to alternate fault-lines with each layer. If you are unsure about this process, ask a local brick layer in your site for help.
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Chapter 3: Building Now that you have the barrel, the base, and your mud ready to go, you are ready to start building your oven. As stated below, there are three (3) phases involved with building the oven, and we will explain each phase separately and also how they fit together to form the finished product. Three phases:
1. The bottom layer, the ramps, and mounting the barrel 2. The middle levels 3. The top Building Phase 1: The first three layers, ramps, and mounting the barrel
The first thing you will need to do is measure the area where you will build the oven. Locate the ideal spot on your base, keeping in mind the oven should not be centered on the base, rather the front of the oven should be near the front edge of the base, along the 45inch side. With this, the wood will have plenty of room to rest on the table behind the oven and the person cooking will not need to lean over and reach quite as far to get their hands inside the oven. The area you need to mark off is 100 cm wide x 98 cm long This area will mark the outside lines of the oven, and when you build you will place the bricks inside of these lines, always preserving this 100 cm x 98 cm area.
Shown in the photo is the base with the initial markings of 100cm x 98cm. The two pieces of paper on the right mark the front two corners, and the paper in the back shows the space for the wood to enter, where no brick will be placed. You should place the bricks on the inside of these lines, always preserving this 100 cm X 98 cm space.
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Once you have your lines drawn, lay down a layer of mud along the inside of these lines, leaving a space between 25 to 30 cm wide for the wood in back, as shown below.
This is an aerial view of the first layer of bricks. The vertical side is 100 cm; the horizontal side is 98cm. The picture shows the space where the wood will enter.
As shown above, you want to place a layer of mud down along the perimeter of the 100cm x 98cm box. From here, you will begin to lay bricks down. In this picture, the oven door will be at the top, and the wood will enter the back side at the bottom of the picture.
Continue to lay your bricks, remembering to lock each layer, and always remembering to leave enough space between bricks to fill with mortar, called ‘liga’ in Spanish.
The final product should look like this, 100cm wide by 98cm long, 3 levels high, with a 25cm - 30cm space in the back for the wood
Now that you have the initial three layers, you will need to make the ramps.
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Construction of the ramps The ramps are necessary because they aid with air-circulation. They add curvature to the inside of the oven, making it easier for the air to continually circulate and heat the oven. You can think of the ramps as a highway for the smoke.
Start the ramps by laying down rocks (roughly the size of two fists) down along the inner left and right sides of the oven. These rocks will serve to fill the space underneath the ramps, so they do not all need to look great or be the same size, just large enough to fill the space and small enough to fit the slanted bricks, as shown below.
Continue to lay rocks down along the inside walls, cover them with a layer of mud, then begin to lay bricks, slanted, as shown in this picture and the one below.
Lay the slanted bricks next to each other. There is no need to use the mud mortar inbetween the bricks in this step.
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Continue to add slanted bricks until you have both sides complete. The long, thin space you have that runs from the wood entrance to the front of the oven is the space for the wood.
Tell the people that you are building this space small because you only want to use a little bit of wood, there is no need for a big space which would need lots of fire wood to fill.
Place rocks underneath the slanted bricks. This gives the slanted bricks something to rest on as additional support. Once you have some small rocks wedged underneath the bricks, cover them with mud. Broken pieces of “tejas” (roof tiles) work well also.
Fill in the space at the top of the slanted bricks with small rocks and mud, just as you did at the bottom in the picture above. Broken pieces of tejas (roof tiles) work well also, as above.
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Once you have completed the ramps, you should have something that looks similar to this.
This view shows the fire chamber, where the wood is going to be located. Once the above is completed, you are now ready to mount the barrel.
Mounting and securing the barrel
The first step to mount the barrel is to cut two (2) bricks as shown above. You need to cut the bricks at more or less a 45 degree angle.
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Place the two (2) bricks with the 45degres angles on the back side of the oven, over the fire door. These will serve to level out the oven. Essentially, the back of the oven will be 4 levels high and the front will be only 3 levels high.
Place the barrel on top, the front end resting on the front end of the first three levels, and the back end on the two 45dregree angle bricks.
This view shows the barrel as it rests on the back bricks. We will use these 45degree angle bricks as wedges, pushing them closer together or pulling them farther apart in an effort to get the barrel completely level.
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Place your level tool (nivel) on top of the barrel to make sure it is level. If not, use the back 45degree angle bricks as wedges, pushing them closer together or pulling them apart in an effort to level the barrel. The barrel must be completely level, if not, what you are baking will not bake evenly.
Make sure to level the oven on all sides, including the front and on the inside rack.
Your barrel is now in place. It should be completely level and locked in place. From here, you are now ready to begin phase 2 of the building process, the middle.
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Building Phase 2—The Middle Layers
The first step is to measure. Lay a few bricks as shown, and measure the distance between the brick and barrel. You want to maintain a space of 5-7cm between the sidewalls and the barrel. Even spacing is important, as without even spacing, you will not be able to bake evenly. Note that the flat brick represents the first layer of bricks. The vertical brick is only vertical for the time being to measure accurately. When you make your sidewalls, always lay the bricks flat and never stack them on end.
Once you have measured on all sides, you are ready to start building up the sidewalls. Lay down your first layer as shown.
Have people working on both sides simultaneously, always remembering to maintain your 5-7cm spacing. It is a good idea to measure each side after every level, making sure both sidewalls are the same height and to make sure you are maintaining a consistent 5-7cm space between the sidewall and the barrel, keeping in mind the barrel is curved, so the distance between the brick sidewall and the barrel with change with every new layer. Just make sure you are maintaining the same distance on both sides.
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Continue to build up the sidewalls, always locking the bricks by alternating the location of the fault line with each new level.
Once you have your sidewalls 5-6 layers high, it is time to measure, y et again.
Measure the height of your sidewalls. You want to have your sidewalls between 1820inches high. The number of levels you place down to get this height will vary from place to place, depending on the thickness of the bricks you are using. If you are using a normal brick, which is about 2.5 inches thick, you will need 6 levels to get your sidewalls to the desired height. Once you have the sidewalls at the right height, you are ready for phase three, the top.
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Building Phase 3:The Top
First, cut two (2) bricks in half, lengthwise.
It is best to use a brick that has been soaking in water, as wet bricks break easier.
This step is not easy; you might not be able to get this on your first try.
Next, use these half bricks that you cut to lay on both the front and back of the barrel, slanted, as support bricks for the top of the oven. Do the same on the opposite side. Refer to the following picture for additional information on these support bricks.
These half bricks will rest directly on the barrel, with a little mud underneath to keep them stuck in place. As shown, you want the brick to lay on the oven, at the front and back of the barrel. They will also rest on the sidewall for support from the bottom. Do this on both sides, leaving you with 4 half bricks placed this way.
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For the top, you want to recreate the ramps that you have on the bottom of the oven, again to aid with air circulation. The bricks that make up the upper ramps will not rest directly against the barrel; instead they will rest on a piece of rebar that runs along the length of the barrel.
Next, you want to cut a piece of rebar 35inches long (the length of the barrel), and place it on the 4 support bricks. In order to secure the 35inch rebar in place, cut into the support bricks by rubbing a piece of rebar against the brick. This creates a channel for the rebar to sit securely on the brick.
After you have your rebar secure on the support bricks, place bricks along the rebar across the length of the barrel. This will be a mirror-image of the ramps at the base of the oven, helping the air to continue circulating.
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The finished upper ramps look like this on both sides. Notice the spacing between the slanted bricks and the barrel. The slanted bricks never touch the barrel, only the rebar, that is suspended 5-7 cm off of the barrel, always maintaining the space for air circulation.
Now that you have the upper ramps on both sides, fill in the space at the front and back of the oven (the space between the support bricks that runs along the upper rim of the barrel). This is shown on the far right of this photo. Next, measure the distance between the two upper ramps, and cut 8 pieces of rebar to this distance. This rebar will be placed across the top of the oven, one piece of rebar per pair of bricks. The middle pair of bricks will need two (2) pieces of rebar, so the chimney can rest securely
These eight (8) pieces of rebar should be between 1521 inches each. Any longer and this means you did not build you sidewalls tall enough, shorter means you built your sidewalls to tall. Once you have your rebar across the top, it is time to place bricks on top of the rebar. There is no science to this process, just place your chimney in the middle of the top, and fill the space around the top with bricks, much like placing pieces of a big puzzle down to fit together.
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Continue to place bricks on the top of the rebar that rest on your upper ramps. Continue to place bricks as if working on a puzzle.
Place triangular pieces of bricks in the space near the chimney. You can also use pieces of tejas (adobe roof tiles) to close off this space. The idea is to close every space with bricks, leaving no room for air to escape.
Next, seal the entire oven in mud. You want to cover everything. You should not be able to see any bricks on your final products, as the entire thing is incased in mud.
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The chimney is made out of a 1 gallon can and can be found around any house. Just hollow out both the bottom and the top, leaving you with a circular tube to serve as the chimney. Place this directly on the rebar above the oven, and then surround it with bricks, covering the entire top surface. When you build the oven indoors, you have to connect an extension tube made out of metal sheet (zinc liso) to take smoke out of the house, through the roof.
Add your layer of mud on the top, covering all of the bricks and sealing the oven to prevent heat loss. The best placement of the chimney is in the middle of the top, or near the front of the oven. With this, the heat will need to travel a farther distance to seek its exit, maintaining more heat within the oven for cooking.
You can make a damper on the chimney by cutting a slit in the side, then fitting a piece of sheet metal (zinc liso) inside the clit. With this, you can control the amount of air that your fire needs to have a consistent, slow burn, thus saving the amount of wood you will use.
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This shows the chimney open
If you do not make the slit in the chimney for the damper, you can always use a roof tile or even a brick, anything to control the flow of air.
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Chapter 4: Finishing Techniques Below are a few additional features you can add to your oven. Cement Sealing: this technique requires a half bag of cement and 3.5 latas (standard 5 gallon bucket) of sand. Sealing the oven with cement will lengthen the life of the oven, it will heat up faster, get hotter, and maintain the heat longer and also be weather proof.
Painting: If you can find colored
dirt at your site, painting is an option to make your oven look better.
The Igloo: You can add an igloo
opening to protect the fire door on the back of your oven. This will help retain more heat and will also protect against excessive winds.
Rounded top: You can make the
oven more of a round shape, as opposed to the more structured look, by adding mud to the sides. Front side igloo: You can also put
the fire door in the front, on the same side as the opening for the oven door. This works great if you are building your oven in the corner of a kitchen or another tight space.
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Chapter 5: Using your oven Now that you have your oven completed, you will need to add sand underneath the rack, inside the oven. This sand helps to regulate the internal temperature of the oven. As the fire is directly below the barrel, the bottom of the oven will be the hottest part. We put sand to help absorb some of this heat, helping to get a more even bake on the top and bottom of the oven. Most ovens call for somewhere between 1-2 latas (standard 5 gallon bucket) of sand to get your even bake. You will have to experiment with the amount of sand that your oven needs, as every oven is different and calls for a different amount of sand. Below are pictures of where to put the sand.
Sand beneath the rack, on the inside of the oven, helping to regulate the temperature.
The First Burn You should heat your oven after it dries, usually after 5-7 days. The first time you bake in your oven will take a long time to heat up, as most of the bricks and mud will still be a little wet and wet bricks take longer to heat up and cannot hold heat very efficiently. You should burn your oven all day, helping it to dry and also to find out exactly how much sand your specific oven will need.
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Chapter 6: General Maintenance and Trouble Shooting General Maintenance
You will need to repair you oven every month or so with white dirt, depending on your usage, in order to seal cracks and help retain heat. Ideally, you should go over the oven after every use. You should build a roof over your oven to provide protection from the elements. Remember that a wet oven will never work properly; it must be 100% dry in order to work efficiently. Trouble Shooting What if my oven is not heating up?
It could still be wet. Make sure it is dry, and then try to use it again. The fire might have gone out. You need to regulate the amount of air touching the fire, so use your chimney damper or open or protect the fire door in the back to allow more or less air in. My oven is not heating evenly and my cookies are burning, what should I do?
You should make sure the sand underneath the rack is the right amount. If your cookies are burning on top, you have too much sand and you should take some out. If your cookies are burning on the bottom, you do not have enough sand, and you need to add sand. If the spacing between your sidewalls (building, phase 2) and the oven are not equal on both sides, your cookies might cook more on one side and less on the other. With this, you are going to have to move your cookies around in the oven while they are baking, giving them a few minutes on the right and then a few minutes on the left side of the oven. This is why it is important to make sure you build your oven evenly, preventing these problems from arising. You can also make sure your oven rack is aligned straight by placing your level inside and adjusting the rack to make sure it is perfectly level. The fire keeps going out, how do I keep it going?
An important note to remember with the size of your fire is the quality of wood you are using can effect your baking. If you use bad wood, you might not be able to keep a consistent fire and will not be able to bake. Also, check your chimney damper and the size of the fire door. A big part of keeping a consistent fire is airflow. You might need to experiment with your oven to get the ideal conditions for baking.
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References •
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Fundación Odorico D’Andrea, Proceso de construcción de horno ecológico ( PDF Presentation), San Rafael del Norte, Jinotega, Nicaragua, 2006 Fundación Odorico D’Andrea/ Cuerpo de Paz Nicaragua, Horno Mejorado, demostración práctica (Brochure), El Coyolito, La Concordia, Jinotega, 23 de Abril del 2008.
Acknowledgements To all the Volunteers in different sectors of Peace Corps Nicaragua, that have contributed to spread this technology. To PC staff for promoting and supporting appropriate technology as food security tools, and specially to our CD George Baldino, for being an enthusiastic activist of this topic. To all the Nicaraguan families that have trusted and adopted this technology and now have become promoters of it inside their communities.
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Co rp s - Nic a ra g ua
Mission Statement
Peace Corps/Nicaragua, through Volunteers and Staff, supports the sustainable development of Nicaraguan communities and their most vulnerable population groups. Volunteers contribute by building the capacity of local leaders and other community members, with priority attention to Nicaraguan youth and the rural poor, to meet their basic needs and improve the quality of their lives.
Pe a c e C o r p s N i c a r a g u a Rep a rto Sa n Jua n, Del Hot el Bra nd t’ s 200 Mts. al Sur, Ma na g ua , Nica ra g ua Apdo. Postal 3256 Pho ne (505) 2270-7510 Fa x (505) 2270-7516
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