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Earthen Oven for our Outdoor Kitchen: the 'Stoven 2'

With the outdoor cooking season almost underway here in Reno it was time to rebuild our Stoven.  About three years ago I created a rocket stove/cob-oven hybrid (see blog post here) to meet our summer food cooking needs.  We live without electricity and fossil fuels at our Be the Change Project and when we can't or don't use our Sun Oven we fire up the Stoven.

For three years our original Stoven was great - it performed well and generally aged well.  It was made mainly of cob with some firebrick used in the burn chamber.  My impetus for making this second version was threefold: First, to make a more durable model; second, to add a water heating cooktop; and third, as part of an overall redesign of our outdoor kitchen.  

While the first Stoven aged well overall - the exterior was perfect (and protected under a roof) and the interior dome showed no damage from three seasons of firings - the shelves which held the grill grate had worn away considerably on both the front and back of the chamber.  This caused the door to fit poorly and made it more difficult to place and hold the grate once the fire was burning.  Now, admittedly, I could have simply mixed up a little cob and repaired the area and gotten years more use but that wouldn't have been nearly as fun as making a much better Stoven and more functional outdoor kitchen.  For this new-and-improved model I incorporated much more firebrick including for all of the grate-holding surfaces.  I had about thirty salvaged bricks left over from my mini-masonry heater project (including halves and pieces) so I used them to build the interior frame of the new Stoven.  The halves and chunks were great fillers (along with regular old red bricks) which save a lot of cob and mixing.  

Construction

I started by laying a layer of regular red bricks over the existing wood platform that held the last Stoven.  Then I played with firebricks for a while to see what shapes I could get.  I wanted a burn basin that was small enough to keep it efficient but big enough to handle some decent sized sticks and a good amount of charcoal for when I roast a rabbit or two.  I wound up laying a layer of landscape pavers for the basin floor and then standing fire bricks all around it save for the wood feed slot.  The pavers were just a little wider than the firebricks and seemed to make a good-sized basin.  This gives me two layers of bricks above the plywood base, more than enough, in my experience, to prevent damaging heat from reaching the plywood.  Also, any gaps between the bricks are quickly filled with ash once I start cooking with the Stoven which act to insulate further.  

I continued building up with bricks for the burn basin (the bottom half of the burn chamber) and then laid some cob on the outside to create a shell and to hold the next layer of firebricks which was reset back from the grate-holding first layers.  In dry Nevada I only had to wait an hour or so for the cob to firm up enough so the bricks could be set on top without causing any splooging.  I should mention that I re-used the cob from the old Stoven.  After hacking it apart with my two young hammer-wielding sons, we collected the pieces in large basins to which I simply added water and used a shovel to break it down further.  I took a little break and let the water do the work of "melting" the cob (overnight is great if you can plan ahead) and then mixed it up a bit with a shovel again.  I love this about cob: it's infinitely re-usable. 

I set the bricks and kept building up the cob on the outside.  The cob does several things:  it adds thermal mass, holds the firebricks together (I smush cob into any large gaps between bricks to serve as mortar, as well), allows me to make a dome and a curved door opening, and creates an aesthetically pleasing form which can be further sculpted and plastered.  Cob is also a super-local product that takes no fossil fuels to create or transport.  I could and would have used solely cob if I didn't have free and salvaged firebricks lying around.  It would have worked just as well and likely have needed some minor touch-ups over time.

To make the dome top, I added layers of cob which slope inward bit by bit and take breaks in between each layer so it can set up.  This is not technically difficult in any way but takes a little time.  My new Stoven was built over three days for a total of maybe 8 hours for one person (without any finish plaster).  I could have made a complete dome like the original Stoven but wanted to add a water heating surface so I inset an old fly pan into the top of the dome.  This made making the top easier and gives me a place to heat a kettle for tea or a pot for hot water to clean the dishes (because we live without electricity and fossil fuels, hot water is sometimes at a premium).  Being on top and outside the Stoven also means the teapot will not get sooty - the one major annoyance with this type of cooking.  And, yes, we'll lose some heat for cooking by having this feature but our desire for hot water trumps that bit of savings.

The feed slot has a brick on its side and another couple odd bricks angled up after it (towards the exterior of the Stoven) to make use of a little gravity to help deliver the sticks more easily into the burn basin.  I also added a little cob there to further extend the feed slope so it would hold sticks in place and prevent them from falling onto whatever shelf I make next to theStoven.

I also tacked on a piece of flagstone to serve as the loading dock at the door.  From the firstStoven I knew that I wanted a larger surface to easily hold my pots and a more durable surface as it is used often.  On the first model, this shelf was made of cob and wore out a bit.

Sculpting the Stoven

After I got the overall structure up I started adding some sculptural elements.  I knew I wanted some sort of fire on the front and as I played with the cob what evolved was a sun with fiery rays emanating from the door.  I realized the back could use some art too so that turned into a moon to go with the celestial theme.

The next layer after the cob is the brown coat.  I used a mix of 2 parts screened sand and 1 part screened clay.  The clay is from our yard and the sand from up the road in the desert.  Both materials are just perfect for building – the clay is quite pure and sticky and the sand has sharp grains of varying size.  It would be entirely possible for all of Reno’s building to be made of cob using these abundant, non-toxic, low-tech, and local materials.  Can you imagine that?  It would be amazing.

I find applying the brown coat to be the most enjoyable of the natural building processes. The screened materials feel so sensual and luscious in the hands and they spread across the walls like butter on hot toast.  Also, there is less pressure to have the coat come out perfectly since it will be covered by the finish plaster anyway.  No pressure and silky materials make for a good natural building time.  

Finish Plaster

After getting the Stoven roughed out I spent several days building our outdoor kitchen.  I made use of old lumber, salvaged granite counter tops from a local tile store, salvaged wood from a cabinetry place, and a sink from the local Habitat for Humanity store.  I plumbed the sink using some leftover half-inch pex tubing and have each sink draining into a bucket that we empty as needed on the few plants in our front yard not on our irrigation system. 

I bought Kaolin clay several months ago to use on finish plaster projects I knew I’d be getting to this spring and summer.  Kaolin is the most commonly used clay for finish plaster.  It is mined in Florida and shipped all around the world, which is why I generally don’t purchase it but make do with what we have or what shows up from pottery stores and pottery classes.  However, we hadn’t been able to find any light clay of late and I wanted to put on some ridiculously beautiful finish plasters around my house.  So, I bought two 50 lb bags for about $25 bucks each. .  (Update:  I just found a great source of local Kaolin-like clay in a dry lake bed just twenty minutes from our house.  Woo-hoo!) 

For the first finish coat I mixed 2 parts screened sand with 1 part Kaolin and added some yellow iron oxide pigment (bought at a hardware store).  The finish plaster goes a long way so I never mix up too much and always keep track of my ratios if I do need a second batch.  The best tool for applying finish plaster on round surfaces is a plastic disc cut out from a 32 oz yogurt container lid.

Overall, this layer came out quite white.  From here I started experimenting with clay paints.  I made a wheat paste and mixed it equally with Kaolin and then added lots more pigment and enough water to get it to a paint-like consistency.  This got me a smooth paint that I was able to brush on all over the first finish coat.  It was a light yellow and served to fill in some of the small cracks that had appeared in my finish plaster.  More pigment and some vegetable-based paint powder (“tangerine” was the name) we found in the kids’ closet made an even richer orange paint that I added for accents.  I am quite pleased with the result and look forward to using this Stoven (and trying, unsuccessfully I am sure, to keep soot off the plaster) this season and for years to come.