Okay, but what are you going to do with it?

Sooo. In my initial plan for the studio we are building, I had planned to use a small wood-burning stove that I picked up on Craigslist about two years ago for a hundred bucks. The title of this post is the question Greg asked me when I arrived home with it in the back of the truck.

Unfortunately, once I had laid everything out on paper when we were contemplating the studio, and I took into consideration the very large clearance from combustible materials that is required for a cast iron wood stove, I realized it was going to eat up a whole lot more floor space than I thought. I haven't solved this dilemma completely, but I'm looking at a few options, including a direct-vent gas (propane in my case) fireplace that recesses into the wall and has a low profile on the inside (most of the stove bumps out of the wall to the outside), and does not require a chimney. I also found a very small Vermont Castings cast iron gas stove that is only 13 inches deep and can sit as close as three inches from the wall since the combustion chamber is insulated. This would eat up very little floor space.

Anyway, I'm still working on this issue and cost is a factor. We'll probably wait until next fall to deal with the heat issue because we can limp along with a small electric heater for the time being, except when the temps drop into the single digits. I just can't store anything out there that will freeze until we solve this issue.

Anyway, I have this old second-hand, wood-burning stove that looks exactly like this... It's a Vogelzang Deluxe Boxwood Stove and that's the image from their website. Mine is buried under a bunch of stuff in the barn at the moment. I figured I'd hang onto it and eventually use it to heat a greenhouse since it turned out not to be ideal for my studio. It's a nice little utilitarian stove, no window, just a cast iron box with a flue. It's pretty cute and you can even cook on it in a pinch. It's perfect to heat a greenhouse if you have a way to move the air around the space. There's even a little gadget that you can add between sections of the stove pipe that will capture much of the heat going up the stove pipe and send it out into the room rather than having it escape to the outside. It makes the stove much more efficient. Anyway, the problem with cast iron stoves is that they get super hot, and once the fire goes out they lose heat pretty quickly. There's just not enough thermal mass to really retain a lot of heat for very long.

Or so I thought... check this out!


http://www.handprintpress.com/ovens/bring-in-the-mud/

This is from Kiko Denzer's webpage. He's the guy I got the original idea from, for Sunny the clay oven. Look at that thing! He's basically created a "clay hat" for his stove and inside this hat is a serpentine tunnel that winds around and around inside that thing. The clay heats up and becomes basically a radiator and the winding design inside there is basically a big heat exchanger, with lots of surface area to soak up the heat. After the clay absorbs the heat traveling through the tunnel, the stove pipe exits "the hat" and the smoke and some of the hot air goes on up out of the roof, leaving most of the heat behind in the Hat. The hat slowly radiates the heat into the room, just like my clay oven radiates heat back into the baking chamber. Genius! (although I do have some concerns about the ability of those spindly legs to support what has to be several hundred pounds of clay. Looks a tiny bit precarious.

Anyway, it sparked an idea about how to heat a future greenhouse, using a stove I already have, and the abundant supply of oak firewood we have accumulated over time.

I could really extend my growing season if I could put a little bit of supplemental heat into a tunnel or lean-to greenhouse, particularly if I use twin-wall polycarbonate or a double layer of poly film. I'd start by taking the legs off the little Vogelzang stove (they're bolted on), and right smack in the middle of the greenhouse, I'd dig down several inches and put a scrap of foam insulation in the hole about 4 x 4 feet square. Then, I'd pour gravel on top of the foam insulation until it was level with the ground. Then, I'd basically build something similar to Sunny, but embed this stove inside the mud dome, leaving the front of the stove exposed, for access to load the wood, build the fire, and clean out ashes. Access to the damper is also in the front part of the stove. You could make a hearth out of the clay too so you could sit by it and warm up when working in the greenhouse in the winter, and even build out to the side, a chamber that could hold your firewood. The heat from the clay would probably get warm enough to help dry the firewood so it burns better, with less smoke, and it would also give you a place to store several days' worth of wood without having it piled up all over the place. I'd cover the stove pipe with a thick tube of clay up to about six feet or so, then stick another damper in the stove pipe at that height, to help draw the air upward, then add that little gadget to capture residual heat that is still in the stove pipe, and then vent it out through the roof. Basically, the stove becomes the firebox for a big masonry heater, and all that clay (probably 12 or more inches thick) would absorb the heat through the walls of the stove, and slowly release it into the greenhouse. You could really make this a massive thermal storage device and really get a lot of bang for your buck with each fire.

I think you could still do what Kiko did and form a small chamber above the firebox that you could use as an oven, and get double duty from this contraption. Not sure what you would want to cook in a greenhouse but, whatever... Although, you certainly could bake bread in there when it is too cold outside to use Sunny.

It would look like a big adobe fireplace in a pueblo except for the cast iron door. By enclosing the stove inside a big envelope of clay/mud, I think you would eliminate any issues of minimum clearance to the wall, and with the exception of the door, none of the surface should get hot enough to actually burn you. The thermal mass of the clay structure should help avoid the extreme temperature swings that you get with a typical wood stove.

One thing you'd need to keep track of is the humidity level in the greenhouse. As a rule, you want a lot of humidity in a greenhouse, and the hotter the air temperature, the more water it holds. This is a good thing when trying to raise plants. However, raising the air temp in the greenhouse way above the outside temperature is going to cause a lot of condensation on the walls/ceiling of the house. This water is going to come from somewhere so you would need to make sure your planting beds are not drying out too much, or figure out a way to recapture the condensation as it runs down the walls of the greenhouse. Hmmm, surely there's a solution for this. People grow food in heated greenhouses at latitudes above 50 degrees so this is not a unique problem. It might be something as simple as having an open tank of water as your humidity source, which slowly evaporates, providing the necessary water for the surrounding air, and then capturing the condensation along the bottom of the greenhouse walls and feeding it back to the drip irrigation system. This could help prevent the soil from drying out. Sounds complicated but I'll research this issue and figure out what other people have done.

This might be a fun project to do when my folks come up sometime. It would be much more challenging than building Sunny, which took the better part of a weekend. My dad would have a blast doing this with us. Based on the amount of clay, sand and straw I used when I built Sunny, a clay heater of this size would probably require at least a full pickup bed each of sand and clay, and probably not as many bales of straw. The straw strengthens the mix but too much straw creates an insulating effect, trapping the heat inside the stove, which was perfect for the clay oven but not what I would want for this heater. I would want the heat moving through the clay walls and out into the room. I'd have to mess around a bit and figure out how little straw I can get away with and still have a strong structure, particularly the chimney part.

Best part about this project is the cost. I already have the hundred-dollar stove. Local clay is free or almost free (I probably can use the tractor to dig some really decent clay out of my pond that will be easy to work with) and coarse sand is a few bucks a ton. Literally. I just need to go to the sand pit and get it. The rest is just manual labor. As for fuel, we have numerous dead trees on our property that need to be dealt with anyway. Much of the wood is useable lumber but the limbs and so forth are perfect for firing this little stove, and we have an almost unlimited supply of them.

If I eventually do this, the greenhouse should be stay comfortable in all but the worst part of winter, and I ought to be able to grow all kinds of cool season veggies well into December or perhaps... even... dare I say it? January????? Eliot Coleman would be proud!

Sunny 2.0: The Big Muddy

Last weekend Greg and I rebuilt the foundation for the clay oven and poured a concrete counter-top. We took the forms off on Tuesday evening and for our first concrete counter-top attempt, it turned out really great. On Saturday (yesterday) Greg headed to Menards for some stuff he needed for installing some drainage tile in some low areas in the vineyard. Before he left, he mixed up some coffee colored stain in a spray bottle and sprayed the concrete. It dried pretty quickly and looks great. We may do another layer of stain once Sunny is finished, then we will seal it.
















While he was gone, I got started on Sunny. I hosed off the concrete and spent some time leveling the sand bed and installing the fire bricks. I leveled the sand, added a little, and slid the bricks into position, and tamped them down with a hammer so they were flush with the edge of the concrete.




















Once done with that, I gathered together all the bags of sand I could find and started building the dome on top of the bricks. The dome will serve as the mold for the oven shell and once the shell is hard enough to support it's own weight, the sand can be pulled out leaving a cavity. I got about half way through building the dome when I realized I might not have enough sand. I stopped, shoveled all of the sand into 5-gallon buckets, and went looking for something to take up some of the space in the dome. After considering several things, including a 5-gallon bucket, I realized that whatever I used needed to be able to fit through the 10-inch tall doorway opening, which would be the only way to remove it. This eliminated the bucket as an option. I eventually settled on four plastic milk containers. I filled them with water and tightened the lids, and arranged them in the center of the circle I'd drawn as the outline of the dome. I then started piling all of the sand back into a dome shape.

Before I built Sunny 1.0 I had read Kiko Denzer's book "Build Your Own Earth Oven" and used it as a guide for my own clay oven. One mistake I made, in spite of the book's indication that it was pretty important, was that I made the door too tall, which caused a lot of heat loss, and took a long time to heat it up to temperature. I had used a slab of quartzite as a sort of lintel and it was unable to withstand the high temperature, and eventually fell apart (well actually it exploded into pink shards).

This time, instead of a horizontal rectangular opening, I'm going to use an arch which will make building a door a bit more complicated but should be a very strong opening.

Back to the sand, once I'd piled up a dome the dimensions of the oven cavity I wanted (17 inches high, 29 inches across) I soaked some newspaper in water and covered the dome with it. This helps to separate the oven shell as it dries, from the sand which will be removed by hand. It makes removing the sand easier, and also prevents sand from clinging to the inside of the shell of the oven, and raining down on your pizza as it cooks. Any bits of paper still clinging to the oven shell will burn out with the first fire.



It was really windy and I had some problems with keeping the newspaper stuck down on the dome, and it kept drying out so I had to periodically mist it with the hose, and finally just put a block of wood on top of it.

I had all of my buckets of mud that I had saved from Sunny 1.0 and it was wet and ready to use so I got started building the oven.



I picked up big handfuls of mud (sand and clay in a 1:1 mix) and started going around the bottom of the dome, building a wall roughly 4 inches thick.

As I moved around the oven in a spiral, the wall got higher and higher. I used a piece of 2 x 4 to firm and shape the wall as I went, and made every effort to keep it a consistent thickness all the way up. The wind helped to quickly dry the mud and stiffen it, but I realized there was some slumping on one side (the mix used there may have been a little wetter than ideal) and so I slowed down the building process to allow the mud to set up a little and gain some strength to support the weight of the wall.

This took the better part of the day and as I got close to the top, I realized I was going to run out of mud before I ran out of dome, so I gathered up a bunch more clay from a hole Greg had dug the other day, and watered it down. I added sand and spent at least an hour trying to get it homogenized by hand. By the way, I don't recommend this method. My hands are still extremely sore, and I can barely type.

I managed to get most of the clay and sand incorporated together but not before using more water than I should have, leaving me with a very wet mix.

I decided to let the mix set up overnight hoping that the clay minerals would rehydrate and take up some additional water into their actual crystal structure, making for a smooth mix with plenty of strength. The two separate mixes may be a problem when I go to finish the oven if the new mix and the old don't bond together well, but I think I have a solution for that. I have a bunch of 4 inch galvanized nails that I'm going to stick into the existing shell and use them as a kind of rebar or "key" to tie the two together. It may still crack but since the insulation layer will be going over it, I'm not really worried about heat loss, just the strength of the shell.

Today (Sunday) I hope to finish the inner shell, finish the insulating layer, and cut the door opening. I think I'll leave the sand inside for a few days just to support the "weak area" as long as possible.

Once the insulation layer is finished I'll let it set up for a couple of days, and then mix up a third layer of mud that will include fine chopped straw, sand, and clay. This will be the finish or plaster layer and the texture will allow me decorate it either by sculpting a design or adding some pebbles in a cool pattern. After that, the only thing left to do is put on the stucco textured coating on the vertical faces of the cinder block foundation, and then paint it. Oh, and start cooking pizza...

The last picture demonstrates the difference in color between the Old Sunny clay and the new clay dug out of the ground a couple of days ago. The sand to clay ratio is about the same so hopefully it will shrink pretty uniformly as it dries. My only concern is that the Old Sunny clay has been subjected to high temperature (but not high enough for it to undergo vitrification obviously) so it may not respond the same way to firing the oven.

Guess we'll find out. I can always start over again. It's only dirt, right?

Construction Zone: Sunny 2.0

Saturday morning we got up early and decided to tackle taking apart the clay oven (Sunny). The plan was to remove the clay dome and hopefully save the clay to reuse in the new oven. I wasn't sure this was going to work because the inner shell of the oven had been exposed to some pretty big, very hot fires, many burning for four to five hours. I wasn't sure whether the inside of the oven had reached a temperature high enough to vitrify the clay, which would prevent us from softening it and reusing it. I had a suspicion we'd be dealing with a large, turtle-shell-shaped BRICK. Greg headed to Menard's (like Home Depot) for some supplies we'd need, and I set to work demolishing Sunny.













I took a few photos during the process and used my rock hammer, which has been collecting rust on Greg's workbench for years, and started pounding on the oven. After several hard whacks, I started making slow progress. I headed out to the barn to look for the sledge hammer thinking that was the right tool for the job, but couldn't find it. Anyway, as I broke through the outer layer of "cob" a mixture of clay, sand and chopped straw, I realized it was coming apart in a distinct layer, separate from the inner clay-sand layer, exactly as I had built it.

I threw the outer layer pieces into the wheelbarrow, and as I broke through the dense inner layer, I threw those pieces into a big black tub that normally serves as a sheep water trough. The demo took about an hour and when I was done, I removed the fire bricks and set them aside, leaving the cinderblock foundation and the sand bed that had held the fire bricks.



Greg and I came up with a plan and got busy building the wood and melamine forms to serve as the outer shell of the concrete countertop, which we were going to pour on top of the cinder blocks. We made an outer frame and an inner frame to keep the concrete from covering the sand bed.


















Once the framing was done, Greg rounded up some rebar and some pieces of a cattle panel to serve as structural support for the concrete. We debated how we wanted to finish the edge of the countertop and just decided we'd leave a sharp edge and then use a sanding block or his orbital sander to round the edges over once everything is finished. Greg picked up some concrete stain at Menard's that can be sprayed on after the concrete dries, so it isn't just plain old gray. Since the clay is a warm tan/brown color, it should blend in well. We plan to stucco the vertical surfaces of the cinder blocks with a surface-bonding cement and then paint that the color of the trim on the house so it should blend with the brown of the concrete pretty well.

Greg borrowed an electric concrete mixer from someone he works with and he'd calculated how much concrete we'd need so once we'd formed up the frames we quit for the day and planned to start early Sunday morning pouring the concrete.


Before we cleaned up our mess, I filled the buckets and water trough containing the remains of Sunny with water from the hose. I figured we'd leave it overnight and hopefully by the following morning the water would have softened the clay enough to determine if we'd be able to reuse it.

On Sunday, we got up early so we could get going on the concrete pour. I checked the buckets and sure enough, everything had become a mushy, gritty goo. Perfect. All I'd need to do is let it settle and skim off the water layer on top of each bucket, add a little extra sand and clay and we'd have plenty of material to build a bigger, thicker-walled oven.

Greg set up the rebar inside the frame and we fired up the mixer. Greg ran the mixer and I shoveled the wet concrete into the frame. We used seven 80-lb bags of concrete to fill the frame, and once we were done, Greg used a 2 x 4 to smooth the mix and level it, then we left it to set up. After it had set up somewhat, Greg worked on finishing the surface as smoothly as possible. We may need to polish it with the sander before we stain and seal it. Maybe not though. It looks pretty good to me.

We wet it down with a hose and covered it with a tarp to slow down the drying process to allow it to cure.

Once we had rinsed out the concrete mixture, we decided to try using it to homogenize the recycled cob. We processed each bucket as it's own batch, and ran the mixer for several minutes on each batch. This worked really well and managed to break up most of the chunks of clay. Once we get to the point of rebuilding the actual oven, things should go pretty fast since I won't be starting from scratch. It takes quite a bit of time to manually mix the ingredients for the oven. Having the mixer was a huge time saver.

One thing I'm going to do differently this time is put a sheet of aluminum on top of the sand layer and below the fire bricks. This should help reduce the heat loss through the bricks into the sand layer. Another thing I'm going to try is a one to two inch insulation layer of clay/sand/straw and vermiculite on top of the clay/sand thermal layer. I hope to really cut down on the heat loss through the walls of the oven by incorporating the vermiculite as an insulator. I'm also going to increase the wall thickness of the thermal layer to 5 inches. It will take a little longer to heat the oven up to temperature but it should stay hot much longer by doing all of these things. This will potentially allow several hours of cooking, starting with pizza and breads, which require very high temperature but cook very fast, followed by slow roasting of vegetables and chicken as the oven slowly cools. Finally, by loading the still-warm oven with a stack of firewood, the residual heat will help to dry it out so it will be ready for the next firing.

A well fitting door and possibly a chimney with a damper are also design features that I did not use in the old oven but may use with Sunny 2.0. By putting in a chimney above the door, I hope to be able to get more complete combustion inside the oven, cut down on the soot around the door (which gets all over you and doesn't look particularly attractive). A tight fitting door will be a lot more functional and safer than stacking bricks in the opening, which is how we closed up the old oven. This oven will definitely be a lot more user friendly.

We wet it down twice a day on Monday, and again on Tuesday morning, and once Greg got home from work, we took the forms off. Here's what it looks like thus far. The hole in the middle is exactly the size of the fire bricks. We will install them after we wet down and tamp the sand bed. We planned everything out so once we put the bricks back in the hole, they will be at the same height as the surface of the concrete and everything will be flush and smooth, so the pizza peel will slide in and out easily.

Here's how it looked today (Tuesday) when we took off the frame.

Here's a link to my inspiration, a 9 foot tall oven called "Maya" in a restaurant in Corvallis, Oregon built by Kiko Denzer...

http://www.intabas.com/images/bigmuthuoven.jpg