Building a simple rocket stove

As part of my interest in low-tech cooking I’ve wanted to build a rocket stove. Last summer I spent time at a lake cabin with a beach fire ring made of cement blocks. The gentle on-shore breeze inspired me to try making a forced ventilation rocket stove with the cement blocks.

The base was a V of solid blocks. The V was topped with more solid blocks. The chimney sat above the point of the V, and was two 8×8″ hollow cement blocks. I chinked gaps between the blocks with piles of dry sand.

I only got to play with it one afternoon, but it worked quite well. I used flotsam on the beach for fuel, mostly 1/2″ diameter stuff. The fire really roared and was quite smokeless. Several hours after the fire was out I returned to dismantle things and burned myself on the still hot blocks.

Dismantling my mud oven

Back when I built my oven, I’d been using Kiko Denzer’s book (now in new edition). He suggested an oven could be built on saw horses with a wooden plank subfloor, but that it would burn through eventually. I’ve previously reported my notes of that problem happening (here) and (here).

The burning problem reached the point where I was sure the oven was losing lots of heat via air coming in from the floor. I’ve enjoyed the oven and want a more permanent one. It was time to dismantle the first oven.

This post is really to share observations of what can be learned in the demolition.

First, its not hard to demolish. I did it by hand with a garden trowel as pry bar, breaking off the outer shell, which I mostly saved at the raw materials for the next oven. Breaking up the inner shell was also easy, and it was not very fired, as shown below. Finally, the burn spot and depth of burn is worth noting, my 2×6’s were half char in the center area.

Kiko Denzer on my Blogroll

I think its worth making some notes about why I add people to my blog roll.

In this case its Kiko Denzer, author of Building a Mud Oven and other books. I used his book to create my oven, and have been pondering the lessons that it is teaching me about the difference between how I live and how the oven wants me to live.

Its also worth noting that the Google Blog search for “mud oven” produces some very interesting results. In fact, I just re-ran the search to make this post and Google had already added my previous post “Oven Luck” to its results — in about 3 minutes. Further worth noting is there is now RSS of Blog searches, this has important implications for my previous strategy pieces on being a Web 2.0 organization.

Oven Luck

This is the next in my series of oven-related reflections. I’m coming to understand how different a mud oven is from a microwave oven. The latter heats just the item you want. Usually this is a small item, its heated quickly (seconds or minutes) and the oven is cold afterward. Kiko Denzer writes about super-insulated ovens, I’m learning to bank coals to one side behind a wall of pre-heated fire brick. Each strategy keeps the oven warm longer.

Last weekend we came into a bounty of salmon, a result of the Palouse Prairie School celebration . We had friends coming over, a former miller, and I decided to make bread. And a casserole with the salmon, and why not a fruit crumble. Things got further out of hand when I decided to smoke some of the salmon (I mean, I’m around, doing chores, tending fires, why not run the smoker at the same time?) My smoking does not get the meat very warm, so I’ve usually finished in the oven on low. Then my wife remembered one of our guest’s food allergies and decided to make a second fruit crumble.

So, oven is 550F by 4PM, bread goes in. Bread out in 20 min, spuds, casserole and first crumble in at 5:40. Trade for second crumble while we eat. After cleaning kitchen, fish into 250F oven till bedtime. Oven still 250F an hour later when fish comes out and still 150F the next morning. Kiko has posted a nice summary reflection on his firing experiences, importantly, he describes the value of drying his wood in the last heat of the oven

In the traditional potluck, guests cook at their house and bring finished dish to the party. What about bringing raw food and baking it? Guests could bring more food than would be eaten and take home leftovers. Some items could be baked during/after dinner and taken home whole. If we understood what to do in a 200+ oven overnight, the host could put something (roast?) in at bedtime.

Another baking experiment, smoked roasts

The weather is really chilly for late April, about 40F at mid-day when it should be in the mid-50’s. The oven has been staying pretty dry in its tarping since the last adventure. I decided to make white sour dough and roast a chicken with rice. I had a hankering for brown/wild rice, and the COOP has a nice blend.

I was raising the bread in the kitchen where it was cool because I got ahead of myself and put the yeast in at 9AM. By 1PM it was ready for the first punch down.

Here is the timeline:

• 1:40 ignition, on top of a “V” of 4 bricks to funnel the air and to keep the floor of the oven cooler.
• 2PM clear smoke, added fuel, roaring chimney; Whole chicken into Lil Chief smoker.
• 3PM more fuel, it had burned down to coals
• 3:30 more small fuel for hot finish; oven is warm on top; bread shaped to rise
• 4PM Fire pulled out to Weber grill, a couple cherry pieces pushed to the side and bricks in place to shield it. Extra brick covering chimney hole. Sealed door and chimney to soak; Pork sirloin roast into Weber, not very hot. The experiment I tried was putting some green cherry pruning’s into the bottom of the Weber before dumping in the coals. Resulting smoke was not very appealing.
• 4:15 Oven steaming/smoking. Underside of floor warm, not smoking, but there is char visible between the 2×6 floorboards.
• 4:25 650F, bread in (I was worried it would burn on the bottom) Chicken had been in smoker most of this time, without marinate. Its skin is warm and smoky. I placed chicken on top of onion rings and put pre-cooked rice on the sides. Chicken’s dish is covered.
• 4:50 Bread looks beautiful, but not done.
• 5:10 Bread out, oven 425F; pork, carrots and potatoes in covered dish go in.
• 6PM Chicken out, its great
• 7:15 Roast out, temp 300F

Since I am not yet coming up with uses for the 300F oven after cooking the second meal, I’m starting to think about enclosing the oven in a room to capture the heat like from a masonry stove.

Authentic problems weave together many strands

At work we have been working on some case studies of learning portfolios and among our observations are that the authors are using the portfolio (or some might say Personal Learning Environment (PLE)) as a means to work on a problem facing themselves (and some community) and they are weaving together multiple modes of thinking, such as art, politics and science.

I’ve been writing about my explorations of a mud oven I built and have found the fringe edge of a community exploring cob building, mud ovens, baking and the arts therein. The quotes below struck me as a demonstration of the weaving of multiple strands while working on a problem.

A home of this community is Kiko Denzer and Hand Print Press.

Here is Kiko’s statement from the Introduction to Dig Your Hands in the Dirt:

“Art is…”

Art is many things, but here what I mean by “art” is that kind of experience by which humans learn.

Working with mud, sand, and straw is a way to teach geology, engineering, physics, history, drawing, composition, and design. It is also a way to teach social skills, like cooperation. But more important than just what it teaches is how it teaches…

The artifact below will be dated when you read this, but look at the weaving of art, craft, food, science (emphasis mine).

Circa March 11, 2008, by email:

What follows is a schedule of hands-on workshops on how to make wood-fired ovens out of earth, good sourdough bread, and natural plasters to sculpturally enhance any building; also a list of slide presentations on earthen and natural building. These are offered by Kiko Denzer, and others, as noted. Feel free to share/forward the info; or let me know if you’d like to be removed from this list. (We also have a possible APPRENTICESHIP opportunity for the right person(s). More about this at the end of the email.)

Below are dates, locations, and information specific to each workshop. Registration info and a general description of the workshops are at the end.

WORKSHOPS:

April 12-13
Ovens & Bread
Philomath, Oregon, Gathering Together Farms
Gathering Together Farm is a local, community-sponsored farm. We’ll be building an oven for their public restaurant and event operation. Limited number of openings available. $175, includes lunch.

MAY 26-27 OR May 31-June 1
Ovens & Bread
NE Portland, Oregon
A residential oven in a neighborhood setting. Probably bi-lingual, English/Spanish! Limited openings. $175, includes lunch.
(This is also a good time to make mud in Portland, during the annual Village Building Convergence, featuring speakers, events, and natural building projects around the city. See cityrepair.org for more.)

June 9-13
Earth & art for your home: design, sculpture, & decoration with natural materials
Coquille, Oregon, at the North American School of Natural Building, with Linda Smiley and others
Natural plasters, paints, and finishes to design, sculpt, and help finish an existing cob cottage. We’ll start with a review of the principles of design, site analysis, 3-dimensional space and spatial dynamics, and practical beauty. Then we’ll get muddy; work will be interspersed with discussion and demos covering technical, design, and materials issues, including a full range of earthen and lime plasters, clay paints, and sculptural mixes. Explore and experiment to gain practical experience to apply to your own design problems. The site features a broad array of earthen and natural buildings and related techniques. Contact the school at 541-396-1825, or see fee and registration details online at http://www.cobcottage.com

July 10-20, or 26-27
Ovens & Bread
Pringle Creek Community, Salem, Oregon
Registration is limited

August 23-24
Ovens & Bread
near Burnt Woods, Oregon, at the site of the future Oregon Folk School

PRESENTATIONS
Sunday, March 16
Building community out of the mud, at the Community Built Association CONFERENCE,
Asilomar center, Monterrey, CA
A conference of public artists, park designers, and community builders. Founded in 1989, the Community Built Association is a not-for-profit association of professionals who work with local communities and volunteers to design, organize, create, and reshape their own physical environments through the creation of parks, playgrounds, murals, or sculpture. http://www.communitybuilt.org. Or contact Leon Smith: leon@earthplay.net

May 30th, noon
Mud 101: Earthen building and other arts
A slide presentation at Portland’s Green Home Show
Portland Expo Center, Portland (http://www.betterlivingshow.org)

June 1-8
Oven demos & presentations
Ashland, Oregon:
Demos and presentations will accompany a special workshop for students and members of the Willow Wind alternative school community. For more info, contact handprint@cmug.com or call 541-438-4300, after April 31.

How Workshops work:
If you can make mud pies, you can build with earth. Good material is often underfoot. Practical, beautiful, dirt cheap, and faster than you think, mud is also sculptural, colorful, and rich, whether you make ovens, benches, garden walls, or houses. And you can do it with your kids! “Mud ovens” were the original masonry ovens (brick is, after all, fired clay). The ovens we make bake beautiful bread (and anything else), and perform as well as the fancy $4,000 Italian ones. You can build a simple one in a day, learn about cob and natural building – and make the best pizza and breads.

Instructors: KIKO DENZER & HANNAH FIELD
Workshops cover everything you need to know to make an oven and bake anything in it, as well as Hannah’s simple approach to naturally leavened, “artisan” breads. Kiko & Hannah have taught at Bob’s Red Mill, Andrew Whitley’s Village Bakery (UK), the King Arthur Flour Company, and at the Bread Baker’s Guild of America’s “Camp Bread” in San Francisco. Kiko is an artist/ builder and author of Build Your Own Earth Oven (bread chapter by Hannah), & Dig Your Hands in the Dirt: A Manual for Making Art out of Earth (Hand Print Press). Hannah baked professionally for organic bakeries in the UK, and is also an organic gardener and massage therapist. We don’t have a conventional oven — every other week, we bake 25 pounds of whole-grain sourdough in a mud oven. It’s a staple food. Our philosophy for workshops is that we all participate, we all learn, and we all teach. Groups are generally interesting, diverse, and fun. We also believe that the cooking (and growing) of food is essential to true culture. Our hope is that , by working, cooking, learning, and eating together, we maintain the living fabric of a peaceful community and culture.

FORMAT: Both days combine oven-making with bread-baking, adjusted to suit participants. By the second day, we’ll have a “temporary oven” to bake in, and a more permanent oven to finish. We start working at 9 am, and are done by 5 pm.

ACCOMODATIONS are not provided, tho some hosts may have space and and facilities for camping.

FEES: $175 per person for two days of hands-on learning, lunches, and snacks. For those with limited, low, or fixed incomes, we can and do reduce fees; please inquire.

TO REGISTER for the “earth and art in your home” course in Coquille, call 541-396-1825, or goto cobcottage.com.

TO REGISTER for all other courses: Send a check or postal money order for 50% of the course fee, payable to Kiko Denzer, at POB 576, Blodgett OR 97326. Note your first and second choices for workshop dates. Registration fees are non-refundable unless we can fill your space immediately. 20% discount for full pre-payment by 3 weeks before your chosen workshop. When we get your payment, we’ll send confirmation and other info.

MORE INFO/QUESTIONS: Please call 541-438-4300, or email handprint@cmug.com.

BOOKS: The new oven book features a super-insulated design, Hannah’s bread chapter, a chapter on mobile, community, & “rocket” ovens; plus lots of new photos & drawings and completely revised & updated text. Price is $17.95, shipping is free (check or money order to Hand Print Press, POB 576, Blodgett OR 97326. Look inside it (and other titles) at handprintpress.com.

OTHER COURSES (Please note: separate instruction/contact/registration info):
SEE cobworkshops.com, naturalbuildingnetwork.org, &/or do a websearch for your local area (“natural building,” “earth” or “cob” or “clay ovens” etc.). In CA, look up Emerald Earth, the Permaculture Institute of N’n CA (PINC), and many others.

APPRENTICESHIP OPPORTUNITY: This is a home-and-community based invitation to share in and learn from the life of a family that is trying to live, learn, grow, and eat as close as possible to their (rural) home, inspired by a vision of “every man (& woman) ‘neath their vine and fig tree, living in peace and unafraid” — and in community with their (urban and) rural neighbors. Projects include gardening, infrastructure (greywater, etc.), plastering, repair/maintenance of cob buildings, rural community events (including a local folk school start-up), ovens, art & sculpture projects, bread & other food prep, watching out for noisy boys (2 & 5 yrs), playing in the creek, a small publishing business, etc. Asking 4 days/wk of help, cash contribution for room and board, plus (reduced) workshop fees. If you’re interested, write and tell us about yourself and your interests.

Drying oven, more experiments

I haven’t baked since my last episode where I burned the floor boards under the oven. I’ve been thinking about how to warm the oven and dry it without overheating the floor. What I tried, with fair success was putting 8 broken red brick on the floor, end to end, with a thumb width between them to let air flow under the fire I would build on top of the brick.

I started at 9 AM with a small pine fire, then slowly added charcoal briquettes. I kept things going with bits of wood and more charcoal, but never very hot. After noon the outside was warm (uncovered and in the full sun, ~50F by then). I measured the surface temperature with a hand-held IR thermometer. The highest reading was 117F on the top, 85 on the sunny side, 75 on the north side.

About noon, I pushed the coals to the sides of the oven (off the brick) and added kindling and charcoal. My goal was to put more heat at the edges of the oven. Around 2PM I put in 6-8 pieces of mixed wood, mostly firewood scraps. By 4PM it was coals and I pulled out the red brick and the coals and allowed 30 minutes soaking Several of the red brick were hot thru my insulated fire gloves. I should have sequestered the coals with the hot red brick and left all that in the sides of the oven. An oval oven would facilitate this chipmunk-cheek strategy. Need to look back at how I thought the oven deck was too small and augment that by 6″ left and right.

I had repaired the inner face of my baking door by rebuilding the cob and had propped it in the doorway of the oven to fire the clay for awhile. I took care to put wet cloths in the door to get a tight seal and covered the chimney with a rag and a board and brick as well as shutting the damper. At 4:30, the thermometer read 450F, which seemed too hot for the bread in metal pans. I put a couple of the red brick back into the oven. They were warm to bare hands. And put the bread on the brick. It would have been better to be prepared with something thermally lighter to serve as hot pads. I think I have an old BBQ grill that could provide a 1/2″ spacer.

In 45 minutes the bread was beautiful and the temp read 350F (disappointing, given my first experience with how long the oven stayed hot. Did the earlier bonfire approach get a lot more heat into the mass?). I pushed the bricks to the sides of the oven and slid in 2 quiches. Twenty minutes later the quiches still were very runny, so they moved to the conventional oven.

With the quiche out, I put in a covered pyrex dish with a lamb shank that said it should be braised at 300F. The lamb came out at 8:30 and seems moist and completely cooked, but the temp has fallen to 200F. I think there is radiant heat in the oven that belies the air temp measured by the thermometer. Things cook better than the thermometer would make you think.

I still don’t want to make a massive foundation, next step is to design a better insulated floor that can take high heat and build another oven.

Next baking episode

Its been cold and wet. Today was the second day of warming, predicted to reach 38F. I decided to bake again. Starting about 1PM I lit a fire, mostly pine firewood in pieces 2″ diameter. It was burning hot and clean by 1:30 and I kept poking in a few more bits to keep it going well. At 3:15 the bottom of the 2×6 floor was not warm and the top of the shell was still cool. There was a lot of water to dry out of the clay, despite the tarp covering.

We were going ice skating, so I loaded in several pieces of pine and put the baking door in place, with its two 1″ breathing holes. Even before we left there was a dark creosote smelling smoke. When we returned at 4:20 the fire was burned down to coals; it seemed fairly warm, but not hot. I tossed in 5 pieces of kindling and went off to prepare the bread (Laurel’s Kitchen Bread Book, the herbed potato bread) which had been in its first rise since 3:00.

By 4:45 the kindling was burned down. I noticed a thin whiff that seemed more like smoke than steam under the floor of the oven! Kiko warns that ovens on sawhorses fail by burning thru. The floor boards were warm, not hot and the outside of the shell was warm under the insulation blanket. I had remembered to put two bricks into the oven when I lit the fire and now I pushed all the coals to the chimney opening and put the bricks in front of the coals to protect the food from the radiant heat of the coals. I did not pull out the coals.

By 5:00 I had tossed in 4 baking spuds, 1 Butternut squash (halved and cleaned then re-assembled) and a pie plate with an acorn squash cut in 1″ wedges (Great recipe that I found on http://epicurious.com, the squash is cooked with oil, salt and pepper, then dressed with a lime/oil/garlic/herb vinaigrette.) I was letting the bread rise again and put two baguette loaves into the oven about 5:25. My hope was that I had allowed enough time for the oven to soak.

An oven thermometer just inside the door read 300F when the bread went in. I pulled the spuds and acorn squash at 5:50, one spud was not done. All had black burn marks. The bread seemed soft on the end near the door but there were toasty smells. I decided to turn the loaves end for end.

At 6:20 I pulled the bread, which was black on the bottom but seemed properly baked otherwise. The temp read 250F.

Conclusions. I managed to get the firebrick very hot but the baking door leaks too much air. This caused the bread to burn while the temp did not seem hot. Spuds and Butternut squash black spots confirm this hot floor. Baking in this oven in these conditions, I need to provide a container for the food to buffer the heat from the floor. The dish with the acorn squash was hot enough to boil the vinaigrette when I poured it on and it had some hard-to-clean stains from the baking process — but the food was unburned.

I also need to seal the baking door better to prevent the drafts that were making the temp read low. This probably also means plugging the chimney more than the damper does. And after that many hours of firing, I need to allow more soaking time.

The long range conclusion is that the oven needs a real foundation and better insulation. Kiko promised in an email to me that his 3rd edition of the book has instructions for a well insulated (top and bottom) oven. I need a roof as well (if not totally indoors).

Baking at 20F

I’ve been waiting for a chance to continue with the ideas from the last post. I decided to make potato herb bread today, despite the weather. Its been cold and dry for most of a week and was about 20F when I got out to the oven at 10:30am. Pealing the plastic covering off gave a surprise — a layer of ice condensed between plastic and oven.

• 11 AM fire lit
• 1 PM still frosty outside, installed R-19 cover over much of the oven
• 2 PM pulled out most of the fire, pushed some coals to the back and placed a brick in front to shield. Should have put the brink in the oven an hour earlier to warm
• while to oven soaked, I tossed an unstuffed chicken into the Weber, as planned. This time, the coals were not smokey — they were really just coals, so I dumped on a handful of alder smoking “chips” more like really coarse sawdust — huge cloud of smoke almost immediately. I placed chicken on aluminum foil to protect if from the heat.
• The chicken got stuffed with wild rice brown rice, plus onion, and herbs
• 2:30 PM the oven was 300F when the food got in, including 3 sweet potatoes. It started to snow
• 3:55 PM going to pull in the food, it smelled nicely smoky when I peaked at 3:40

Reflection-in-action: the small baking dish I used for the chicken was too shallow and the fat from the chicken was overflowing when I tried to slide it out.

Reflection, the oven cools off too fast in this environment, I either need to learn from Kiko Denzer’s new book about super insulating the oven (Kiko’s new book promises this) or get it into an indoor setting. One thought is to build a new one in my greenhouse.

Mud Oven and Weber Grill – roasting

I got a late start today on the oven. I got a fire going with lots of prunings, mostly 1″ diameter and less. When I came back to check on it, flames were a foot out the top of the 4 foot stovepipe!

The problem I decided to work on was the ways to use the Weber grill. I dug out coals into the Weber grill (one of the 18″ diameter ones). Covered, with vents open, the grill threw off a huge plume of smoke. I had started a roast by searing it in a cast iron pot and I put the roast into the Weber to smoke. The smoke was not the best smelling, because I had some pine and what-not in the fire, so I didn’t leave the roast more than 10 minutes. (It added a better smoke smell to the meat than the fire indicated.)

BUT, the idea I’m having is to make sure I use cherry and apple prunings in the late stage of the fire, so that those are the coals I’m pulling out. Then the meat goes into that smoke for 20 minutes while the oven soaks and then the meat goes into the oven to roast. I suppose that spuds could go into the Weber too, maybe cut and oiled.

The other experiment I’m trying is leaving some fire in the oven. I didn’t burn the fire long enough and its only 275F in there. I pushed all the bigger coals to the back and put in a couple bricks between the fire and the front of the oven. This reduces my cooking space by half, but the bricks block direct heat from the still flaming coals from reaching where I would bake. Since I got this late start, I’m only going to cook a thermometer and a couple spuds tonight, the roast is in the conventional oven. Next time, roast chicken maybe.

PS. The spuds cooked nicely. The temp fell to 225F (maybe 212F) as the oven remained damp the whole time (steaming madly under its leaky tarp, now supplemented with another layer).

It snowed last night and is still snowing lightly this AM. The Weber is covered, the oven is clear of snow.