A while back I read about the Green Rocket Pizza Oven, the most innovative pizza oven I've ever seen. It uses some of the wood combustion efficiency concepts developed over the past 35 years by people like Dr. Larry Winiarski. Unfortunately, it looks like the Green Rocket Pizza oven may only be available to people in the Dallas, TX area. As I read more about rocket stoves, I came to realize how important they could be to the people in developing countries. As you may know women and children are spending many hours daily as they travel long dangerous distances trying to collect firewood. Also, millions die from the smoke pollution in their homes. The folks at Aprovecho are working hard to improve this situation around the world. While there are few stoves for sale online and even on amazon, this seems like an area for a lot of home inventors.
I've been thinking, these rocket stoves are cooking for hours using the amount of wood I might use as kindling just to start my oven. Could I redesign bread/ pizza ovens for greater efficiency? I decided to take this on as a project to be cast using castable refractory a material, like portland cement but with the ability to withstand very high temperatures (above 2000°F). This product is pretty expensive by itself (about $1/ pound) but can be mixed with perlite for a less expensive castable material. Many people are using low cost cob style ovens
This is the process I used.
This is the process I used.
1. Determine the castable ratio to use.
I made several samples of castable material using between 100% refractory and 20% refractory. Here are some findings:
I made several samples of castable material using between 100% refractory and 20% refractory. Here are some findings:
While the 100% and 50% castings were very hard and durable, I found the 33% casting had ideal density (0.6 grams/ cubic cm) and excellent insulation qualities. Castings at 25% and 20% did not appear to have enough strength to be useable. As you can see from the photo, the 20% casting didn’t even hold together when I pulled it out of the plastic cup mold.
I was in Cash and Carry, the restaurant supply store and saw a perfect mold for the oven dome: a 24” steel wok.
This is how in envisioned the oven.
Foundation: Made the base out of 20 standard 8x8x16 cement blocks. Construction of this base was straight forward. If you don’t have experience with masonry, a book on the subject may be all you need. Standard mortar mix.
Casting the dome
Casting the dome was surprisingly quick (less than 30 minutes) once all the pieces were in place.
Casting the dome was surprisingly quick (less than 30 minutes) once all the pieces were in place.
I put plastic over the wok and put a piece of 6” stove pipe in the center, in the event I need a chimney. I’m fairly confident the oven can vent out the door, but it is a lot easier to make the hole now rather than trying to cut the cast refractory later. The mix was 2 gallons of castable refractory (about half of a 50 pound bag) and 4 gallons of perlite. This photo is prior to pushing the mix into place.
I pushed the mix against the sides of the wok, flattened the top by tapping with a board and then carefully pulled the stove pipe out.
Creating the combustion chamber and chimney
The stove pipes and elbow were put into place. (much fiddling needed to put them together inside the blocks)
The stove pipes and elbow were put into place. (much fiddling needed to put them together inside the blocks)
Mixed up a 33% refractory/ 67% perlite mix to fill the void around the stove pipe. Compacted it around the spaces with a stick and smooth the exterior.
Here is the un-molded dome sitting in the approximate final location. Stovepipe fits well.
Creating the oven floor
I chose to cover the cinder blocks with 1/4 inch HardiBaker cement board. It is thin, durable, and heat resistant. Since it can lose strength over 800°F, I cover it with a 40% cement/ 60% perlite mix about 1 inch thick and then smooth and level it. Notice the plywood form to ensure even thickness and level.
I chose to cover the cinder blocks with 1/4 inch HardiBaker cement board. It is thin, durable, and heat resistant. Since it can lose strength over 800°F, I cover it with a 40% cement/ 60% perlite mix about 1 inch thick and then smooth and level it. Notice the plywood form to ensure even thickness and level.
Walls
For the walls, I used 10 common red brick laid flat with three in front and rear and then two in the middle. On top of these flat brick, I put five fire brick on edge. While I’m glad to be using firebrick here because they are 4” tall instead of 3.5 inches, the main reason I’m using firebrick instead of common brick is they are what I had on hand.
I narrowed the opening with two more cut brick so there is room for the peel while minimizing heat loss through the front.
For the walls, I used 10 common red brick laid flat with three in front and rear and then two in the middle. On top of these flat brick, I put five fire brick on edge. While I’m glad to be using firebrick here because they are 4” tall instead of 3.5 inches, the main reason I’m using firebrick instead of common brick is they are what I had on hand.
I narrowed the opening with two more cut brick so there is room for the peel while minimizing heat loss through the front.
For the grate under the fire, I cut up an old barbecue grate using a saw-z-all.
The test firing went pretty well once I got the fire going. I had an easier time once I used cardboard instead of just paper and sticks. The “rocket” sound is pretty cool when the draft gets going. The oven reached 450° in about 20 minutes which was so quick the pizza stone broke. I will cement it back together using masonry cement and also attach a refractory deflector plate to the bottom to take the brunt of the flame’s intensity.
Since I wanted the door to curve, I had to create a mold to cast the shape. I used an old piece of corrugated plastic and drywall screws to construct the mold. Imbedded in the form is an old masonry trowel to form the handle.
Bottom line: this oven was a lot of fun but I found it difficult to maintain an even temperature and there was a lot of ash deposited on the pizzas. Recommendations?
1) Check out the work of Jon and Flip at the Haiti Rocket Stove project. They are making some great rocket ovens.
2) Consider a white oven in which the baking area is fully enclosed and separate from the fire and ash.
1) Check out the work of Jon and Flip at the Haiti Rocket Stove project. They are making some great rocket ovens.
2) Consider a white oven in which the baking area is fully enclosed and separate from the fire and ash.
Stucco and tile
Two layers of Type B stucco (rough textured) were applied along with some decorative elements.
Thank you
Thank you to those with information about rocket style ovens and stoves. One of the best was a lead I got from Kiko to Jon and Flip and their Haiti Rocket Stove Project. Great introductory video and usefulphotos. Thanks also to Dave at the Green Rocket Pizza Oven and of course Dr. Larry Winiarski.
© 2005 Bill Funkhouser Contact Me
Two layers of Type B stucco (rough textured) were applied along with some decorative elements.
Thank you
Thank you to those with information about rocket style ovens and stoves. One of the best was a lead I got from Kiko to Jon and Flip and their Haiti Rocket Stove Project. Great introductory video and usefulphotos. Thanks also to Dave at the Green Rocket Pizza Oven and of course Dr. Larry Winiarski.
© 2005 Bill Funkhouser Contact Me